The Influence of Polymers on the Supersaturation Potential of Poor and Good Glass Formers

pharmaceutics

Article The Inﬂuence of Polymers on the Supersaturation Potential of Poor and Good Glass Formers

Lasse I. Blaabjerg 1 , Holger Grohganz 1,* , Eleanor Lindenberg 2, Korbinian Löbmann 1 , Anette Müllertz 1 and Thomas Rades 1,3 1 Department of Pharmacy, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark; [email protected] (L.I.B.); [email protected] (K.L.); [email protected] (A.M.); [email protected] (T.R.) 2 Idorsia Pharmaceuticals Ltd., Hegenheimermwattweg 91, CH-4123 Allschwil, Switzerland; [email protected] 3 Faculty of Science and Engineering, Åbo Akademi University, Tykistökatu 6A, 20521 Turku, Finland * Correspondence: [email protected]

Received: 16 August 2018; Accepted: 19 September 2018; Published: 21 September 2018

Abstract: The increasing number of poorly water-soluble drug candidates in pharmaceutical development is a major challenge. Enabling techniques such as amorphization of the crystalline drug can result in supersaturation with respect to the thermodynamically most stable form of the drug, thereby possibly increasing its bioavailability after oral administration. The ease with which such crystalline drugs can be amorphized is known as their glass forming ability (GFA) and is commonly described by the critical cooling rate. In this study, the supersaturation potential, i.e., the maximum apparent degree of supersaturation, of poor and good glass formers is investigated in the absence or presence of either hypromellose acetate succinate L-grade (HPMCAS-L) or vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) in fasted state simulated intestinal ﬂuid (FaSSIF). The GFA of cinnarizine, itraconazole, ketoconazole, naproxen, phenytoin, and probenecid was determined by melt quenching the crystalline drugs to determine their respective critical cooling rate. The inherent supersaturation potential of the drugs in FaSSIF was determined by a solvent shift method where the respective drugs were dissolved in dimethyl sulfoxide and then added to FaSSIF. This study showed that the poor glass formers naproxen, phenytoin, and probenecid could not supersaturate on their own, however for some drug:polymer combinations of naproxen and phenytoin, supersaturation of the drug was enabled by the polymer. In contrast, all of the good glass formers—cinnarizine, itraconazole, and ketoconazole—could supersaturate on their own. Furthermore, the maximum achievable concentration of the good glass formers was unaffected by the presence of a polymer.

Keywords: glass forming ability; amorphous; degree of supersaturation; precipitation inhibitor; pKa

1. Introduction The increased focus on combinatorial chemistry and high-throughput screening in drug discovery has led to an increase in poorly aqueous soluble drug candidates, with low and variable bioavailability in pharmaceutical development [1]. In an effort to overcome this challenge, various enabling formulation techniques are currently being investigated. Among these, amorphization of the drug has been shown to increase the apparent solubility of drugs, i.e., leading to supersaturation of the drug with respect to the most stable crystalline form, thereby increasing the driving force for absorption of the drug [2,3]. The ease with which such drugs can be amorphized is known as their glass forming ability (GFA). A classiﬁcation system of GFA based on the recrystallization tendency of drugs during cooling and heating cycles has previously been proposed [4]. Drugs which recrystallized during cooling of

Pharmaceutics 2018, 10, 164; doi:10.3390/pharmaceutics10040164 www.mdpi.com/journal/pharmaceutics Pharmaceutics 2018, 10, 164 2 of 14 the melt at a cooling rate of 20 K/min belonged to GFA class 1, whereas GFA class 2 drugs did not recrystallize during cooling of the melt at 20 K/min, but recrystallized in the following heat cycle at a heating rate of 10 K/min. Finally, GFA class 3 drugs neither recrystallized during cooling of the melt at 20 K/min nor during the following heat cycle at 10 K/min [4]. Classes 1, 2 and 3 represent poor, modest and good glass formers, respectively. This classification system based on arbitrary categories was further substantiated in a later study that revealed that the drugs can be classified according to their inherent crystallization tendency independent of the predefined categories [5]. The new classification system is based on the critical cooling rate, i.e., the slowest cooling rate during melt quenching that results in amorphization of the drug [5]. GFA class 1 drugs inherently have critical cooling rates above 750 K/min, GFA class 2 drugs have critical cooling rates between 10 and 20 K/min and GFA class 3 drugs have critical cooling rates below 2 K/min [5,6]. The dissolution of an amorphous drug may result in a “spring effect”, leading to a fast generation of a supersaturated drug concentration, with respect to the thermodynamic equilibrium solubility. However, this may be followed by rapid precipitation, which limits the potential solubility advantage of the amorphous drug [7]. Drug precipitation is a result of nucleation and crystal growth as the drug is in a thermodynamically unfavorable state when supersaturated. For a given drug, a higher degree of supersaturation increases the risk of precipitation [8,9]. The degree of supersaturation is defined as the ratio between the activity of the dissolved drug in a supersaturated solution and the activity of the drug in a saturated solution of the thermodynamically stable form [10]. However, the thermodynamic activity of a drug in a supersaturated solution in a fasted state simulated intestinal fluid (FaSSIF), as used in this study, is difficult to determine since the drug may become incorporated into micelles or other colloidal species present in FaSSIF [11]. Therefore, the concentration of the solubilized drug is used instead of the activity to calculate an apparent degree of supersaturation (aDS):

aDS = Csupersaturation/Cequilibrium (1) where Csupersaturation is the concentration of the drug in a supersaturated solution and Cequilibrium is the concentration of the drug in a saturated solution. Polymers have been exploited in drug development to stabilize the amorphous form of the drug, either by reducing the rate of nucleation and/or the rate of crystal growth of the drug in the solid state [12]. However, in contrast, it has been shown that a polymer can also promote nucleation of the drug as was shown for acetaminophen in the presence of poly(acrylic) acid compared to pure acetaminophen when investigated by hot-stage microscopy [12]. Additionally, polymers can also inhibit precipitation of the drug in a supersaturated solution, which may result in a “parachute effect”, maintaining the supersaturated concentration of the drug for a longer period of time [7,13,14]. The inhibitory effect of the polymer may simply be explained by mediation of an increase in drug solubility, which decreases the degree of supersaturation and thereby the driving force for precipitation. Furthermore, polymers can also increase the viscosity of the solution, thereby increasing steric hindrance (decreased nucleation) and decrease the effective diffusion coefficient (decreased crystal growth) of the drug [3]. Finally, polymers can interact specifically with drug molecules in solution, inhibiting both nucleation and crystal growth [15]. As the polymers may work in a multitude of ways to stabilize the drug in supersaturation, it is difficult to predict the effect of a specific polymer [16]. Hypromellose acetate succinate (HPMCAS) and vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) are amongst the most often used polymers in recently marketed amorphous drug products [17]. Several studies have investigated the influence of polymer concentration on the inhibitory effect of precipitation during supersaturation of drugs and found that concentrations as low as 0.001% (w/v) to be effective [18,19]. For the selection of the polymer concentrations to investigate, a more pragmatic approach is to assume that the achievable polymer concentrations in vivo range from 0.05% to 0.5% (w/v) based on a 1 g formulation containing 10% (w/w) polymer dispersed in the small intestinal fluid volume in the fasted state (105 ± 72 mL) [20]. Pharmaceutics 2018, 10, 164 3 of 14

To study supersaturation of a drug, the solvent shift method is widely used [21–24]. In this method, supersaturation is induced by dissolving the drug in an organic water-miscible solvent in which it is highly soluble and then transferring the solution into an aqueous acceptor medium where the drug has a low solubility. Van Eerdenbrugh et al. (2014) studied the supersaturation propensity, i.e., the time until precipitation at a fixed aDS, of 50 different drugs by the use of a solvent shift method and monitored the time until crystallization of the drug in the supersaturated solution occurred. The study proposed a classification system based on three categories: class I drugs crystallized within 150 s, class II drugs within 1 h and class III drugs did not crystallize within 1 h. A later study also applied the solvent shift method to induce supersaturation of six different drugs at a fixed concentration (100 mg/mL) in phosphate buffer and proposed another classification system using four categories: “Fast drugs” crystallized within 15 min, “moderate-fast” drugs within 3 h, “moderate-slow” drugs within 6 h and “slow” drugs between 6 and 12 h [22]. References [21,22] were unsuccessful in correlating their respective classification systems of supersaturation propensity of a drug with its GFA, which may be explained by the use of a fixed aDS to study the supersaturation propensity. A recent study proposed a standardized supersaturation and precipitation method (SSPM) to determine the inherent supersaturation potential of a drug, i.e., the maximum achievable aDS [23]. In this solvent shift method, a highly concentrated solution of the drug is titrated into an acceptor medium in which the drug is much less soluble. As the titration induces supersaturation the drug in the acceptor medium, the drug will eventually precipitate and the maximum achievable aDS, i.e., the potential of the drug to supersaturate, is determined as the concentration at which precipitation occurs during titration. Three lower concentrations are additionally tested relative to the maximum achievable aDS and the times to precipitation are determined [23]. It has been shown that the influence of a low amount of organic solvent (e.g., 2.0% v/v dimethyl sulfoxide used in the SSPM) on the solubility of the drug can be neglected [25]. A later study showed that GFA of a drug and its supersaturation potential, i.e., the maximum achievable aDS, may indeed be correlated [24]. Here, the inherent GFA of a drug was classified according to the previously mentioned classification system based on the critical cooling rate of the drug and the inherent supersaturation potential of the same drug was determined by the SSPM previously developed [5,23]. The study showed that the supersaturation potential of GFA class 3 drugs was higher than that of GFA class 2 drugs [24]. As mentioned above, a few studies have attempted to correlate the GFA of a drug with its potential to supersaturate, but to the authors’ knowledge, no studies have previously investigated this potential correlation in the presence of polymers. This study aims to further investigate the inherent supersaturation potential of poor and good glass formers in the absence and presence of a polymer. The inherent GFA of the selected drugs is determined by melt quenching using a method previously proposed [5]. The supersaturation potential of the respective drugs is determined by the use of the SSPM proposed by Palmelund et al. (2016).

2. Materials and Methods

2.1. Materials Itraconazole, naproxen and phenytoin were obtained from Chemie Brunschwig (Basel, Switzerland). Cinnarizine, ketoconazole, probenecid, sodium chloride, sodium hydroxide and sodium phosphate dihydrate were obtained from Sigma-Aldrich (Steinheim, Germany). Dimethyl sulfoxide was obtained from VWR Chemicals (Søborg, Denmark). SIF powder was obtained from Biorelevant (South Croydon, UK). HPMCAS-L was gifted by Dow Wolf Cellulosics (Bomlitz, Germany) and PVPVA64 was obtained from BASF (Basel, Switzerland). All materials were used as received.

2.2. Determination of Thermal Stability The thermal stability of the drugs was determined using a TGA Discovery (TA Instrument, New Castle, DE, USA) as reported previously [5]. Data analysis was performed using Trios software Pharmaceutics 2018, 10, 164 4 of 14 version 3.3.0.4055 (TA Instruments-Waters LLC, New Castle, DE, USA) to calculate the weight loss between 298 K and the drug’s melting point (Tm) + 20 K. The experiments were conducted in triplicate.

2.3. Determination of Glass Forming Ability by Melt Quenching The critical cooling rate was determined using a DSC 8500 (PerkinElmer, Zürich, Switzerland) as reported previously [5]. The critical cooling rate, i.e., the slowest cooling rate that resulted in a full amorphization of the sample was determined using the selected cooling rates shown in AppendixA. Data analysis was performed using Pyris software version 11.0.0.0449 (PerkinElmer, Zürich, Switzerland). The experiments were conducted in triplicate.

2.4. Determination of pKa The pKa of the drugs was determined using a SiriusT3 apparatus (Sirius Analytical Instruments Ltd., Forest Row, UK) ﬁtted with an Ag/AgCl double-junction reference electrode and an overhead stirrer at a temperature of 298 K controlled by the Sirius software. UV-metric pKa titrations were carried out in 1.5 mL ion-strength-adjusted water (0.15 M KCl), titrating with either 0.5 M HCl or 0.5 M KOH using nitrogen as purge gas. Titrations were carried out in the pH range of pH 2 to pH 12 with an initial concentration of the drug of 30 mM. All measurements were conducted in triplicate.

2.5. Preparation of Fasted State Simulated Intestinal Fluid FaSSIF was prepared from a commercially available SIF powder as speciﬁed by the manufacturer (Biorelevant, South Croydon, UK). Phosphate buffer was prepared with 3.954 mg/mL monobasic sodium phosphate, 0.420 mg/mL NaOH, and 6.186 mg/mL NaCl dissolved in puriﬁed water (SG Ultra Clear UV 2002, Evoqua water Technologies LLC, Barsbüttel, Germany) and adjusted to pH 6.5 using either 1 M NaOH or 1 M HCl. SIF powder was dissolved in the phosphate buffer (2.24 mg/mL) and stirred for 2 h at ambient temperature before use.

2.6. Determination of Equilibrium Solubility The equilibrium solubility at 310 K of the investigated compounds was determined by the use of a µ-DISS Profiler (Pion, Billerica, MA, USA) using the experimental settings shown in AppendixB. An excess amount of the crystalline drug was added to the vessels containing either FaSSIF (pH 6.5), 0.05 or 0.5% (w/v) PVPVA64 in FaSSIF or 0.05 or 0.5% (w/v) HPMCAS-L in FaSSIF. The pH of the solution was measured by a Sension+ PH31 electrode from Hach (Düsseldorf, Germany). The equilibrium solubility was taken as the maximum drug concentration, no later than 24 h into the experiment. The solution was filtered using a 0.25 µm cellulose acetate Q-MAX® RR syringe filter (Frisenette Aps, Knebel, Denmark) to remove all particles in the media, which may interfere with the in-situ UV measurements due to light scattering. The experiments were conducted using at least three replicates for each drug. The equilibrium solubility (after 24 h) in pH adjusted FaSSIF was determined using reverse phase high-pressure liquid chromatography (HPLC). 200 µL saturated drug solution in a 0.5 mL Pro cup was centrifuged at 23,000 g (298 K) for 20 min in an Eppendorf Centrifuge 5417R (Eppendorf, Basel, Switzerland). 10 µL of the sample was diluted with 990 µL acetonitrile and analysed by HPLC using a SPD-M30A detector, SIL-30AC auto-sampler, LC-30AD pump and CTO-20A oven from Shimadzu (Reinach, Switzerland). The mobile phase consisted of acetonitrile and 0.05% trifluoroacetic acid and the flow rate was 1.5 mL/min. The injection volume was 1.0 µL (except for itraconazole, where the injection volume was 20 µL) and the separation was conducted using a Phenomenex Kinetex 2.6 µm EVO C18 column (100 Å, 50 × 2.1 mm) (Brechbühler, Schlieren, Switzerland). The column oven was set to 322 K and standard curves were prepared in the range of 0.06 µg/mL to 1000 µg/mL for each drug (r2 > 0.99). The investigated UV wavelength for each drug was: cinnarizine (252 nm), itraconazole (258 nm), ketoconazole (225 nm), naproxen (272 nm), phenytoin (218 nm) and probenecid (250 nm). The experiments were conducted in triplicate. Pharmaceutics 2018, 10, 164 5 of 14

2.7. Determination of the Supersaturation Potential Supersaturation of the drugs in FaSSIF with and without polymers (0.05 or 0.5% (w/v) HPMCAS-L or PVPVA64) was induced using a solvent shift method developed previously [23]. The concentration of the drug in the stock solution was found by determining the maximum concentration in the acceptor media before precipitation at a total DMSO concentration of 2% (v/v). Standard curves for all drugs were prepared by adding aliquots (20–50 µL) of the drug dissolved in dimethyl sulfoxide (1–50 mg/mL) into FaSSIF until immediate precipitation was observed. Precipitation was detected by a shift in the baseline of the UV spectrum, diversion from linearity between absorbance and concentration of the drug and by visual inspection. The stock solution was used to induce supersaturation in FaSSIF. 200 µL of stock solution was spiked into 10 mL FaSSIF (310 K), and stirred with a cross bar magnet at 100 ± 3 rpm to ensure complete mixing within the 10 s. The concentration of the drug in solution and the time until precipitation were measured in-situ using the second derivative of the UV-absorbance in the µ-DISS Proﬁler until precipitation occurred (or for a maximum of 24 h). The second derivate of the UV-absorbance was used to minimize interference from particle light scattering. The induction time (tind) was taken as the time at which the concentration of the supersaturated solution had decreased by 2.5%. The experiment was conducted for each drug using a minimum of three replicates.

2.8. Statistical Analysis The equilibrium solubility, supersaturation potential and maximal concentration during supersaturation are given as the mean ± SD. The samples were compared by analysis of variance (ANOVA) using Microsoft Excel 2013 (Microsoft, Redmond, WA, USA). A statistical p value > 0.05 was considered significant. Data in figures denoted with an asterisk (*) are statistically significantly different from the control.

3. Results

3.1. Determination of GFA of Drugs The GFA of a drug can be classified experimentally by determination of the critical cooling rate using melt quenching in a differential scanning calorimeter or minimal milling time using vibrational ball milling [5,6]. For classification using melt quenching, the thermal stability upon melting of the six selected drugs was initially investigated by thermogravimetric analysis. All drugs degraded by less than 5% (w/w) upon melting (data not shown) and were therefore deemed suitable for classification by melt quenching. In this study naproxen, phenytoin and probenecid could not be made fully amorphous even when using cooling rates of the melt of 750 K/min, which means these three drugs have critical cooling rates higher than 750 K/min and therefore belong to class 1 with respect to GFA, i.e., these drugs are poor glass formers. In contrast, cinnarizine, itraconazole and ketoconazole could be prepared in an amorphous form using cooling rates of the melt below 2 K/min and are therefore class 3 drugs with respect to GFA, i.e., good glass formers (Table1). These findings are in line with previous classifications reported in the literature [5,6]. It should be noted that even though it was not possible to fully amorphize GFA class 1 drugs on their own, several studies have shown that GFA class 1 drugs, such as naproxen, can form glass solutions using a polymer, another drug or an amino acid as co-former [26–28]. Pharmaceutics 2018, 10, x 6 of 14

Table 1. Tm, Tg, classification of glass forming ability, critical cooling rate and pKa of the investigated drugs.

Drug Tm (K) a Tg (K) a GFA Class Critical Cooling Rate (K/min) pKa (Acidic/Basic) Naproxen 429 278 b 1 >750 4.2/- PharmaceuticsPhenytoin2018, 10, 164 569 - 1 >750 8.0/- 6 of 14 Probenecid 468 - 1 >750 3.3/- Cinnarizine 393 288 3 1 -/2.0 c, 7.6 Itraconazole 439 332 3 1 -/4.0 Table 1. Tm,Tg, classification of glass forming ability, critical cooling rate and pKa of the investigated drugs. Ketoconazole 419 319 3 1 -/3.3, 6.2 a a a b c DrugData from Blaabjerg Tm (K) et Tal.g (K)(2018); GFAPartial Class recrystallization Critical Cooling during Rate cooling (K/min) of the melt; pKa (Acidic/Basic) Data from Naproxenreference [29]. 429Abbreviations:278 b Melting point1 (Tm), glass transition >750 temperature (Tg), glass 4.2/- forming Phenytoinability (GFA). 569 - 1 >750 8.0/- Probenecid 468 - 1 >750 3.3/- c 3.2.Cinnarizine Determination of 393 Equilibrium 288 Solubility with 3 and without Polymer 1 -/2.0 , 7.6 Itraconazole 439 332 3 1 -/4.0 KetoconazoleThe equilibrium419 solubility 319 of the drugs 3 was determined to 1 calculate their respective -/3.3, 6.2 apparent degreea Data of supersaturation. from Blaabjerg et al. (2018);Solubilityb Partial ratios recrystallization of the investigated during cooling drugs of the in melt; presencec Data from of either reference HPMCAS- [29]. Abbreviations: Melting point (T ), glass transition temperature (T ), glass forming ability (GFA). L or PVPVA64 relative to theirm solubility in pure FaSSIFg are shown in Figure 1. The respective equilibrium solubility of the drugs in FaSSIF is shown in Table 2 and the equilibrium solubility of the 3.2. Determination of Equilibrium Solubility with and without Polymer drugs in the respective media is shown in Appendix C. TheFor cinnarizine, equilibrium itraconazole, solubility of ketoconazole the drugs was and determined phenytoin, to the calculate solubility their of respectivethe drug was apparent higher degreein presence of supersaturation. of 0.5% (w/v Solubility) polymer ratios compared of the investigatedto 0.05% (w drugs/v) polymer in presence for ofboth either PVPVA64 HPMCAS-L and orHPMCAS-L PVPVA64 relative(Figure to 1). their In solubilitycontrast, infor pure naproxen FaSSIF areand shown probenecid, in Figure the1. The solubility respective was equilibrium similar in solubilitypresence of theeither drugs 0.5 inor FaSSIF0.05% is(w shown/v) PVPVA64. in Table 2Furthermore, and the equilibrium the solubility solubility of the of the two drugs drugs in thewas respectivelower in presence media is of shown 0.5% ( inw/ Appendixv) HPMCAS-LC. compared to 0.05% (w/v) HPMCAS-L (Figure 1).

FigureFigure 1. SolubilitySolubility ratio ratio of of the the model model drugs drugs in fasted in fasted state state simulated simulated intestinal intestinal fluid fluid(FaSSIF) (FaSSIF) with withhypromellose hypromellose acetate acetate succinate succinate L-grade L-grade (HPMCAS-L) (HPMCAS-L) (left (left) )and and vinylpyrrolidine-vinyl acetateacetate copolymercopolymer (PVPVA64)(PVPVA64) ((rightright)) (drug(drug inin purepure fastedfasted statestate simulatedsimulated intestinalintestinal fluidfluid (FaSSIF)(FaSSIF) isis givengiven aa ratioratio ofof 1).1). Table 2. Solubility of the investigated drugs in fasted state simulated intestinal fluid (FaSSIF), It is well known that the addition of a polymer can increase the solubility of a drug as seen for pH adjusted FaSSIF and FaSSIF + 0.5% w/v hypromellose acetate succinate L-grade (HPMCAS-L). phenytoin and ketoconazole in presence of either 0.05 or 0.5% (w/v) HPMCAS-L or PVPVA64 Solubility in FaSSIF Solubility in pH Solubility in FaSSIF + 0.5% (w/v) comparedDrug to pure FaSSIF [15]. Unexpectedly, for probenecid and cinnarizine, the solubility only increased in presence of(mM) 0.05 and 0.5%Adjusted (w/v) HPMCAS-L, FaSSIF (mM) but not PVPVA64,HPMCAS-L compared (mM) to pure FaSSIF.Naproxen Furthermore, for 10.5 the± 0.4remaining drug:polym 6.1 ± 0.3 (pHer combinations 6) of probenecid 6.5 ± 0.4 (pH and 6) cinnarizine, as wellPhenytoin as any combination 0.02 ± 0.004of polymer with 0.13 ±naproxen0.002 (pH and 6) itraconazole, 0.12 the± 0.012solubility (pH 6) was either Probenecid 7.1 ± 0.3 8.0 ± 0.2 (pH 6) 8.6 ± 0.3 (pH 6) similarCinnarizine or decreased with 0.06 respect± 0.004 to their solubility 0.02 ± 0.001 in (pHpure 7) FaSSIF (Figure 0.08 1).± 0.003 (pH 7) KetoconazoleFaSSIF prepared as 0.03 described± 0.005 by the manufacturer 0.084 ± 0.006 (pH has 6) a low buffer 0.117capacity± 0.007 and (pH for 6)an ionisable drug,Itraconazole the solubility may 0.001 be± affect0.0001ed by changes 0.001 ± 0.0002to the (pHpH 6)of the medium. 0.0006 Determination± 0.0001 (pH 6) of the pH of FaSSIF showed that the addition of 0.05 and 0.5% (w/v) HPMCAS-L decreased the pH of FaSSIF fromFor 6.5 cinnarizine, to 6.3 and itraconazole,5.8, respectively. ketoconazole In contrast, and the phenytoin, addition the of solubilityPVPVA64 of (0.05 the drug or 0.5% was ( higherw/v)), inas w v w v presence of 0.5% ( / ) polymer compared to 0.05% ( / ) polymer for both PVPVA64 and HPMCAS-L (Figure1). In contrast, for naproxen and probenecid, the solubility was similar in presence of either 0.5 or 0.05% (w/v) PVPVA64. Furthermore, the solubility of the two drugs was lower in presence of 0.5% (w/v) HPMCAS-L compared to 0.05% (w/v) HPMCAS-L (Figure1). Pharmaceutics 2018, 10, x 7 of 14 Pharmaceutics 2018, 10, 164 7 of 14 expected, did not affect the pH. Furthermore, due to the poor buffer capacity of FaSSIF, dissolution of theIt drugs is well themselves known thatcan also the additionchange pH of of a the polymer medium, can e.g., increase solvation the solubilityof the acidic of drug a drug naproxen as seen infor FaSSIF phenytoin decreased and ketoconazolethe pH from 6.5 in presenceto 6.0. of either 0.05 or 0.5% (w/v) HPMCAS-L or PVPVA64 compared to pure FaSSIF [15]. Unexpectedly, for probenecid and cinnarizine, the solubility only increasedTable in2. Solubility presence ofof 0.05the investigated and 0.5% (w drugs/v) HPMCAS-L, in fasted state but simulated not PVPVA64, intestinal compared fluid (FaSSIF), to pure pH FaSSIF. Furthermore,adjusted FaSSIF for the and remaining FaSSIF + 0.5% drug:polymer w/v hypromellose combinations acetate succinate of probenecid L-grade (HPMCAS-L). and cinnarizine, as well as any combinationSolubility of polymer in with naproxenSolubility and in pH itraconazole, Adjusted the solubilitySolubility was in FaSSIF either similar+ 0.5% or Drug decreased with respectFaSSIF to their (mM) solubility in pureFaSSIF FaSSIF (mM) (Figure 1). (w/v) HPMCAS-L (mM) NaproxenFaSSIF prepared 10.5 as described ± 0.4 by the manufacturer 6.1 ± 0.3 (pH has 6) a low buffer capacity 6.5 ± and0.4 (pH for an 6) ionisable drug,Phenytoin the solubility may 0.02 be± 0.004 affected by changes 0.13 ± to 0.002 the pH(pH of 6) the medium. Determination 0.12 ± 0.012 (pH of the6) pH of FaSSIFProbenecid showed that the 7.1 addition ± 0.3 of 0.05 and 0.5%8.0 ± (0.2w/ (pHv) HPMCAS-L 6) decreased 8.6 the ± 0.3 pH (pH of FaSSIF 6) from 6.5Cinnarizine to 6.3 and 5.8, respectively. 0.06 ± 0.004 In contrast, the0.02 addition ± 0.001 (pH of PVPVA64 7) (0.05 or 0.08 0.5% ± 0.003 (w/v)), (pH as 7) expected, didKetoconazole not affect the pH. 0.03 Furthermore, ± 0.005 due to 0.084 the poor ± 0.006 buffer (pH capacity 6) of FaSSIF, 0.117 dissolution ± 0.007 (pH of the6) drugs themselvesItraconazole can also 0.001 change ± 0.0001 pH of the medium, 0.001 ± e.g.,0.0002 solvation (pH 6) of the acidic 0.0006 drug ± naproxen0.0001 (pH in 6) FaSSIF decreased the pH from 6.5 to 6.0. ToTo separate separate the the effect effect of of the the polymer polymer from from the the effect effect of pH of pHon the on thesolubility solubility of the of drug, the drug, the solubilitythe solubility in pH in adjusted pH adjusted FaSSIF FaSSIF (i.e., (i.e.,FaSSIF FaSSIF adjusted adjusted to the to resulting the resulting pH pHof FaSSIF of FaSSIF in presence in presence of polymer)of polymer) was was also also investigated. investigated. For For cinnarizine cinnarizine and and ketoconazole, ketoconazole, an an increase increase in in their their respective respective solubilitysolubility was was seen seen in in presence presence of of polymer polymer compared compared to to pH pH adjusted adjusted FaSSIF FaSSIF ( (pp << 0.01). 0.01). This This implies implies thatthat the the addition addition of of polymer polymer increases increases the the solubility solubility of the of the respective respective drugs drugs (Table (Table 2). 2In). contrast, In contrast, for itraconazole,for itraconazole, naproxen, naproxen, phenytoin phenytoin and and probenecid probenecid,, the the solubility solubility with with and and without without polymer polymer was was similar,similar, implying implying that that the the addition addition of of polymer polymer did did not not increase increase the the solubility solubility of of the the drugs drugs ( (pp >> 0.05) 0.05) (Table(Table 22).).

3.3.3.3. Determination Determination of of the the Supersaturation Supersaturation Potential Potential of of Poor Poor Glass Glass Formers Formers Naproxen,Naproxen, phenytoin andand probenecid probenecid are are GFA GFA class clas 1 drugs,s 1 drugs, i.e., poor i.e., glasspoor formers. glass formers. Their inherent Their inherentsupersaturation supersaturation potential inpotential the absence in the and absenc presencee and of predissolved presence of HPMCAS-L predissolved or PVPVA64HPMCAS-L (0.05 or or PVPVA640.5% (w/v (0.05)) in FaSSIFor 0.5% was (w/v investigated)) in FaSSIF was using investigated the SSPM [ 23using]. the SSPM [23]. TheThe maximummaximum achievableachievable concentration concentration from from solvent solvent shift ofshift naproxen, of naproxen, phenytoin phenytoin and probenecid and probenecidwas similar was to thesimilar equilibrium to the equilibrium solubility ofsolubi thelity respective of the respective drugs, i.e., drugs, aDS = i.e., 1 ( paDS> 0.05) = 1 ( (Figurep > 0.05)2, (Figuregrey bars). 2, grey This bars). means This that means none of that the GFAnone class of the 1 drugs GFA couldclass 1 supersaturate drugs couldon supersaturate their own, which on their may own,be explained which may by thebe explained drugs either by verythe drugs rapidly either crystallizing very rapidly from crystallizing a supersaturated from a solution supersaturated or never solutionsupersaturating or never atsupersaturating all. at all.

FigureFigure 2. 2. MaximumMaximum apparent apparent degree degree of of supersaturation supersaturation of of naproxen, naproxen, phenytoi phenytoinn and and probenecid probenecid in in fastedfasted state state simulated simulated intestinal intestinal fl ﬂuiduid (FaSSIF) (FaSSIF) and and in in FaSSIF FaSSIF in in the the presence presence of of hypromellose hypromellose acetate acetate succinatesuccinate L-grade L-grade (HPMCAS-L) (HPMCAS-L) (left (left) )or or vinylpyrrolidine-vinyl vinylpyrrolidine-vinyl acetate acetate copolymer copolymer (PVPVA64) (PVPVA64) (right (right) ) usingusing the the solvent solvent shift shift method method st standardizedandardized supersaturation supersaturation and and pr precipitationecipitation method method (SSPM) (SSPM) [23]. [23].

Pharmaceutics 2018, 10, x 8 of 14

For naproxen in presence of 0.5% (w/v) HPMCAS-L, as well as phenytoin in presence of either 0.05 or 0.5% (w/v) HPMCAS-L a maximum aDS > 3 could be obtained using the solvent shift method (Figure 2). In contrast, for naproxen, no supersaturation was seen in the presence of 0.05% (w/v) HPMCAS-L (p > 0.05), and for probenecid no supersaturation was seen in the presence of either 0.05 or 0.5% (w/v) HPMCAS-L (p > 0.05). In the presence of PVPVA64 (0.05 or 0.5% (w/v)), a maximum aDS > 3 was obtained using the solvent shift method for phenytoin (Figure 2), whereas no supersaturation was seen for naproxen and probenecid. In an earlier study, it was hypothesized that drugs unable to supersaturate on their own would Pharmaceutics 2018, 10, 164 8 of 14 also not be able to supersaturate in presence of excipients [30]. In contrast, the results presented in this study show that some polymers, i.e., HPMCAS-L or PVPVA64, can enable supersaturation of some ofFor the naproxen GFA class in 1 presence drugs and of consequently, 0.5% (w/v) HPMCAS-L, it appears that as well GFA as class phenytoin 1 drugs incan presence supersaturate, of either but0.05 would or 0.5% on (theirw/v) own HPMCAS-L very rapidl a maximumy recrystallize aDS > from 3 could a supersatur be obtainedated using solution. the solvent A similar shift methodresult was(Figure found2). in In a contrast, previous for study naproxen, in which no supersaturationthe supersaturation was seenpropensity in the presenceof phenytoin of 0.05% with (andw/v ) withoutHPMCAS-L polymer (p > using 0.05), anda solvent for probenecid shift method no supersaturation was investigated was [31]. seen They in the found presence that ofphenytoin either 0.05 on or its0.5% own (w would/v) HPMCAS-L not supersaturate, (p > 0.05). whereas In the presence supersatur of PVPVA64ation of (0.05the drug or 0.5% was (w enabled/v)), a maximum in the presenceaDS > 3 ofwas either obtained HPMC using or PVP the (1.0% solvent (w shift/v)). For method the GFA for phenytoin class 1 drugs (Figure that2), were whereas unable no supersaturationto supersaturate was in theseen presence for naproxen of HPMCAS-L and probenecid. or PVPVA64, it is speculated that a higher concentration of the polymer is requiredIn an to earlier enable study, supersaturation it was hypothesized of the drugs, that drugsas naproxen unable could to supersaturate supersaturate on theirin the own presence would ofalso a high not concentration be able to supersaturate (0.5% (w/v)) in of presence HPMCAS-L. of excipients [30]. In contrast, the results presented in thisThe study solubility show thatof a somedrug in polymers, FaSSIF may i.e., be HPMCAS-L increased by or the PVPVA64, presence can of a enable polymer, supersaturation which in turn of wouldsome result of the in GFA a decrease class 1 drugs of the andaDS. consequently, For phenytoin, it appearsthe maximum that GFA aDS class in the 1 drugspresence can of supersaturate, 0.5% (w/v) HPMCAS-Lbut would onand their PVPVA64 own very was rapidly reduced recrystallize compared from to the a supersaturated maximum aDS solution. in presence A similar of the result lower was concentrationfound in a previous of polymer, study i.e., in which0.05% the(w/ supersaturationv) HPMCAS-L and propensity PVPVA64. of phenytoin Therefore, with for anddiscussion without purposes,polymer the using y-axis a solvent in Figure shift 3 method is changed was investigatedto concentration. [31]. TheyIt should found be thatemphasized phenytoin that on this its own is simplywould a notdifferent supersaturate, way of presenti whereasng supersaturationthe data shown ofin theFigure drug 2. was enabled in the presence of either HPMCFor phenytoin, or PVP (1.0% it is ( wseen/v)). that For the the maximum GFA class achi 1 drugsevable that concentration were unable does to supersaturatenot increase in in the the presencepresence of of increasing HPMCAS-L polymer or PVPVA64, concentration it is speculated for either that aHPMCAS-L higher concentration or PVPVA64 of the (Figure polymer 3). is However,required the to enable solubility supersaturation of phenytoin of in the FaSSIF drugs, in as the naproxen presence could of 0.05% supersaturate (w/v) HMPCAS-L in the presence increases of a fromhigh 26.1 concentration µg/mL to 30.2 (0.5% µg/mL (w/v)) in of the HPMCAS-L. presence of 0.5% (w/v) HPMCAS-L (Appendix C). A similar result isThe seen solubility for phenytoin of a drug in the inFaSSIF presence may of bePVPVA64, increased as by the the solubility presence in of FaSSIF a polymer, in the which presence in turn of 0.05%would (w result/v) PVPVA64 in a decrease increases of the from aDS. 21.0 For µg/mL phenytoin, to 30.1 the µg/mL maximum in the aDS presence in the presence of 0.5% of(w 0.5%/v) PVPVA64(w/v) HPMCAS-L (Appendix and C). PVPVA64 These results was reduced confirm compared that the toreduced the maximum supersaturation aDS in presence potential of of the phenytoinlower concentration in the presence of polymer, of a i.e.,higher 0.05% polymer (w/v) HPMCAS-L concentration and PVPVA64.compared Therefore, to a lower for discussionpolymer concentration,purposes, the i.e., y-axis 0.5% in ( Figurew/v) polymer3 is changed compared to concentration. to 0.05% (w/v It) shouldpolymer, be is emphasized a result of thatincreased this is solubilitysimply a of different the drug way in presence of presenting of a polymer. the data shown in Figure2.

Figure 3. Maximum achievable concentration of phenytoin in fasted state simulated intestinal ﬂuid Figure(FaSSIF) 3. Maximum and in FaSSIF achievable in the presence concentration of hypromellose of phenytoi acetaten in fasted succinate state L-grade simulated (HPMCAS-L) intestinal ( leftfluid) or (FaSSIF)vinylpyrrolidine-vinyl and in FaSSIF in acetate the presence copolymer of hypr (PVPVA64)omellose (right acetate) using succinate the solvent L-grade shift (HPMCAS-L) method SSPM (left [23) ]. or vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right) using the solvent shift method SSPM For phenytoin, it is seen that the maximum achievable concentration does not increase in the [23]. presence of increasing polymer concentration for either HPMCAS-L or PVPVA64 (Figure3). However, the solubility of phenytoin in FaSSIF in the presence of 0.05% (w/v) HMPCAS-L increases from 26.1 µg/mL to 30.2 µg/mL in the presence of 0.5% (w/v) HPMCAS-L (AppendixC). A similar result is seen for phenytoin in the presence of PVPVA64, as the solubility in FaSSIF in the presence of 0.05% (w/v) PVPVA64 increases from 21.0 µg/mL to 30.1 µg/mL in the presence of 0.5% (w/v) PVPVA64 (AppendixC). These results conﬁrm that the reduced supersaturation potential of phenytoin in the presence of a higher polymer concentration compared to a lower polymer concentration, i.e., 0.5% (w/v) polymer compared to 0.05% (w/v) polymer, is a result of increased solubility of the drug in presence of a polymer. Pharmaceutics 2018, 10, 164 9 of 14

3.4. DeterminationPharmaceutics 2018 of, the10, x Supersaturation Potential of Good Glass Formers 9 of 14 Cinnarizine,3.4. Determination itraconazole of the Supersaturation and ketoconazole Potential of are Good GFA Glass class Formers 3 drugs, i.e., good glass formers. Their supersaturationPharmaceuticsCinnarizine, potential2018, 10 itraconazo, x in thele and absence ketoconazole andpresence are GFA class of 3 predissolved drugs, i.e., good HPMCAS-L glass formers. orTheir9 of PVPVA64 14 (0.05 orsupersaturation 0.5% (w/v)) in potential FaSSIF in was the absence investigated and presen usingce of the predissolved SSPM as HPMCAS-L described or above PVPVA64 [23]. (0.05 A previous study showedor3.4. 0.5% Determination (w that/v)) thein FaSSIF threeof the Supersaturationwas drugs investigated could Potential supersaturate using the of Good SSPM Glass on as theirdescribed Formers own, above and [23]. their A respectiveprevious study maximum aDS wereshowed 5.4,Cinnarizine, 31.6that andthe three 42.1,itraconazo drugs indicating lecould and ketoconazolesupersaturate the good glass are on GFA formerstheir class own, can3 anddrugs, supersaturate their i.e., respective good glass on maximum formers. their own TheiraDS (Figure 4, were 5.4, 31.6 and 42.1, indicating the good glass formers can supersaturate on their own (Figure 4, grey bars)supersaturation [24]. potential in the absence and presence of predissolved HPMCAS-L or PVPVA64 (0.05 greyor 0.5% bars) (w [24]./v)) in FaSSIF was investigated using the SSPM as described above [23]. A previous study showed that the three drugs could supersaturate on their own, and their respective maximum aDS were 5.4, 31.6 and 42.1, indicating the good glass formers can supersaturate on their own (Figure 4, grey bars) [24].

FigureFigure 4. Maximum 4. Maximum apparent apparent degree degree of of supersaturation supersaturation ofof cinnarizine, cinnarizine, ketoconazole ketoconazole and itraconazole and itraconazole in fastedin fasted state simulatedstate simulated intestinal intestinal ﬂuid fluid (FaSSIF) (FaSSIF) and and in in presence presence of hypromellose of hypromellose acetate acetate succinate succinate L-grade (HPMCAS-L) (left) and vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right) using L-grade (HPMCAS-L) (left) and vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right) using the the solvent shift method SSPM [23]. Error bars are not visible in figure due to scaling. solventFigure shift method 4. Maximum SSPM apparent [23]. Errordegree bars of supersaturation are not visible of cinnarizine, in ﬁgure due ketoconazole to scaling. and itraconazole in fasted state simulated intestinal fluid (FaSSIF) and in presence of hypromellose acetate succinate For cinnarizine and itraconazole, it was seen that the maximum aDS increased from 5.4 to 8.8 L-grade (HPMCAS-L) (left) and vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right) using Forand cinnarizine from 31.6 to and 70.8, itraconazole, respectively, itin was the seenpresence that of the 0.05% maximum (w/v) HPMCAS-L aDS increased compared from to5.4 pure to 8.8 and the solvent shift method SSPM [23]. Error bars are not visible in figure due to scaling. from 31.6FaSSIF to 70.8,(Figure respectively, 4). In contrast, in thethe presence of of a 0.05%higher (concentrationw/v) HPMCAS-L of HPMCAS-L compared (0.5% to (w pure/v)) FaSSIF (Figuredecreased4). InFor contrast, cinnarizine the maximum the and presence aDS itraconazole, of cinnarizine of a higher it was and seen concentration itraconazole that the maximum to of6.5 HPMCAS-L and aDS 27.0, increased respectively (0.5% from ( comparedw 5.4/v ))to decreased8.8 the maximumtoand a lower from aDS concentration31.6 of to cinnarizine 70.8, respectively, of HPMCAS-L and itraconazolein the(0.05% presence (w/v to)). of For 6.5 0.05% ketoconazole, and ( 27.0,w/v) HPMCAS-L respectively the maximum compared compared aDS into purepure to a lower FaSSIF decreased from 42.1 to 29.2 and 11.0 in the presence of 0.05 and 0.5% (w/v) HPMCAS-L, FaSSIF (Figure 4). In contrast, the presencew v of a higher concentration of HPMCAS-L (0.5% (w/v)) concentrationrespectively. of HPMCAS-L The same trends (0.05% were (apparent/ )). Forfor cinnarizine, ketoconazole, itraconazole the maximum and ketoconazole aDS in in pure the FaSSIF decreaseddecreased from 42.1 the maximum to 29.2 and aDS 11.0 of cinnarizine in the presence and itraconazole of 0.05 and to 6.5 0.5% and (27.0,w/v respectively) HPMCAS-L, compared respectively. presenceto a lower of concentrationPVPVA64 compared of HPMCAS-L to pure FaSSIF.(0.05% (Cow/vnsequently,)). For ketoconazole, it appears thethat maximum the maximum aDS aDSin pure of The sametheFaSSIF GFA trends decreasedclass were 3 drugs apparentfrom can 42.1 be bothto for 29.2 increased cinnarizine, and 11.0 or decreain itraconazolethe sedpresence as well of as and 0.05 be unaffected ketoconazoleand 0.5% by(w /thev) in HPMCAS-L,presence the presence of of PVPVA64arespectively. polymer, compared which The to is same pure intuitively trends FaSSIF. unexpected. were Consequently, apparent Therefore, for cinnarizine, it appears for discussion thatitraconazole thepurposes, maximum and the ketoconazole y-axis aDS in of Figure the in the GFA 5 class 3 drugsispresence canchanged be of both to PVPVA64 concentration. increased compared or Once decreased to again,pure FaSSIF. it asis wellemphasized Consequently, as be unaffectedthat it thisappears is simply by that the the a presencedifferentmaximum way ofaDS aof of polymer,

presenting the data shown in Figure 4. which isthe intuitively GFA class unexpected.3 drugs can be Therefore,both increased for or discussion decreased as purposes, well as be unaffected the y-axis by in the Figure presence5 is of changed to concentration.a polymer, Oncewhich again,is intuitively it is emphasized unexpected. Therefore, that this for is simply discussion a different purposes, way the y-axis of presenting in Figure 5 the data is changed to concentration. Once again, it is emphasized that this is simply a different way of shown in Figure4. presenting the data shown in Figure 4.

Figure 5. Maximum achievable concentration of cinnarizine, itraconazole and ketoconazole in fasted state simulated intestinal fluid (FaSSIF) and in FaSSIF in the presence of hypromellose acetate

Figure 5.FigureMaximum 5. Maximum achievable achievable concentration concentrationof of cinnarizine,cinnarizine, itraconazole itraconazole and andketoconazole ketoconazole in fasted in fasted state simulatedstate simulated intestinal intestinal ﬂuid (FaSSIF)fluid (FaSSIF) and inand FaSSIF in FaSSIF in the in presence the presence of hypromellose of hypromellose acetate acetate succinate L-grade (HPMCAS-L) (left) or vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right) using the solvent shift method SSPM [23]. Pharmaceutics 2018, 10, x 10 of 14

Pharmaceuticssuccinate2018 L-grade, 10, 164 (HPMCAS-L) (left) or vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) (right10) of 14 using the solvent shift method SSPM [23].

AsAs can can be seen in Figure 55,, thethe maximummaximum achievableachievable concentrationconcentration ofof cinnarizine,cinnarizine, itraconazoleitraconazole andand ketoconazole ketoconazole in in FaSSIF FaSSIF in in the presence of HPMCAS-L and PVPVA64 (0.05 or 0.5%0.5% ((ww//vv)))) is is not not affectedaffected to to a practically relevant degree. Howeve However,r, for for e.g., cinnarizine in presence of 0.5% (w/vv)) HPMCAS-L,HPMCAS-L, the the maximum maximum achievable achievable concentration concentration is is higher higher compared compared to to pure pure FaSSIF. FaSSIF. This This means means thatthat the the maximum achievable concentrationconcentration of of a a GFA GFA class class 3 3 drug drug may may not not be be improved improved by by addition addition of ofa polymer.a polymer. This This may may be explained be explained by a fastby a continuous fast continuous crystal crystal growth growth mechanism mechanism at the high at degreethe high of degreesupersaturation of supersaturation of the GFA of class the GFA 3 drugs, class which 3 drugs, result which in the result polymers in the beingpolymers less being effective less compared effective comparedto supersaturation to supersaturation at a lower at degree a lower of degree supersaturation of supersaturation [32]. However, [32]. However, the polymer the polymer may inhibit may inhibitprecipitation precipitation of the drug of the from drug a supersaturated from a supersaturated solution, e.g., solution, via molecular e.g., via interactions molecular betweeninteractions the betweendrug and the polymer drug and or bypolymer increasing or by the increasing viscosity the of the viscosity solution, of the meaning solution, the meaning time that the the time drug that can theremain drug supersaturated can remain supersaturated may increase may in the increase presence in ofthe a presence polymer asof cana polymer be seen as for can cinnarizine be seen for in cinnarizinethe presence in ofthe HPMCAS-L presence of or HPMCAS-L PVPVA64 (Figureor PVPVA646)[ 3,15 (Figure,23]. From 6) [3,15,23]. Figure6 From it is alsoFigure seen 6 it that is also the seeninduction that the time induction for precipitation time for of precipitation the drug from of the the supersaturated drug from the solution supersaturated is very short. solution This is means very short.that the This experimentally means that the determined experimentally supersaturation determined potential supersaturation using the solvent potential shift using method the SSPMsolvent is shiftvery method close to SSPM the thermodynamic is very close to supersaturation the thermodynamic potential supersaturation of the drug. potential of the drug.

FigureFigure 6. 6. Time-concentrationTime-concentration profiles profiles cinnarizine cinnarizine in in fasted fasted state state simulated simulated intestinal intestinal fluid fluid (FaSSIF) (FaSSIF) in thein theabsence absence or orpresence presence of ofeither either hypromello hypromellosese acetate acetate succinate succinate L-grade L-grade (HPMCAS-L) (HPMCAS-L) or or vinylpyrrolidine-vinylvinylpyrrolidine-vinyl acetate copolymer (PVPVA64) using the solvent shiftshift methodmethod SSPMSSPM [[23].23]. 3.5. Correlation between GFA and Supersaturation Potential of Drugs 3.5. Correlation between GFA and Supersaturation Potential of Drugs A previous study has shown that GFA class 3 drugs have a higher supersaturation potential A previous study has shown that GFA class 3 drugs have a higher supersaturation potential compared to GFA class 2 drugs, and thus there may be a correlation between GFA of a drug and its compared to GFA class 2 drugs, and thus there may be a correlation between GFA of a drug and its supersaturation potential [24]. In the present study, the GFA class 1 drugs naproxen, phenytoin and supersaturation potential [24]. In the present study, the GFA class 1 drugs naproxen, phenytoin and probenecid could not supersaturate on their own. However, for some drug:polymer combinations probenecid could not supersaturate on their own. However, for some drug:polymer combinations of of naproxen and phenytoin, supersaturation of the drug was enabled by the polymer. These results naproxen and phenytoin, supersaturation of the drug was enabled by the polymer. These results indicate that GFA class 1 drugs can supersaturate, however, on their own recrystallization from the indicate that GFA class 1 drugs can supersaturate, however, on their own recrystallization from the supersaturated solution occurs very rapidly. Rapid crystallization is also seen during melt quenching supersaturated solution occurs very rapidly. Rapid crystallization is also seen during melt quenching of the drugs, as it was not possible to prepare any of the GFA class 1 drugs in a fully amorphous of the drugs, as it was not possible to prepare any of the GFA class 1 drugs in a fully amorphous form form using cooling rates up to 750 K/min [5,6]. In contrast, all of the GFA class 3 drugs, cinnarizine, using cooling rates up to 750 K/min [5,6]. In contrast, all of the GFA class 3 drugs, cinnarizine, itraconazole and ketoconazole, could supersaturate on their own and are also easily prepared in an itraconazole and ketoconazole, could supersaturate on their own and are also easily prepared in an amorphous form, as their critical cooling rate is below 2 K/min [5,6]. Furthermore, the maximum amorphous form, as their critical cooling rate is below 2 K/min [5,6]. Furthermore, the maximum achievable concentration of the GFA class 3 drugs was unaffected by the presence of a polymer. These achievable concentration of the GFA class 3 drugs was unaffected by the presence of a polymer. These findings further substantiate the correlation between GFA of a drug and its supersaturation potential. findings further substantiate the correlation between GFA of a drug and its supersaturation potential.

4. Conclusions

Pharmaceutics 2018, 10, 164 11 of 14

4. Conclusions In this study, the inherent GFA of six drugs was determined via melt quenching. Additionally, the inherent supersaturation potential of the same drugs was determined by the use of a solvent shift method using the µ-Diss Profiler to induce supersaturation of the drug in the absence or presence of predissolved polymer in FaSSIF. The GFA of the drugs was successfully classified according to a previously developed classification system with naproxen, phenytoin and probenecid belonging to GFA class 1 (poor glass formers) and cinnarizine, itraconazole and ketoconazole belonging to GFA class 3 (good glass formers). The GFA class 1 drugs naproxen, phenytoin, and probenecid showed no supersaturation potential on their own. However, for some combinations of naproxen and phenytoin with HPMCAS-L or PVPVA64, supersaturation of the drug was enabled by the presence of a polymer. These findings indicate that poor glass formers can supersaturate. However, on their own recrystallization from the supersaturated solution occurs very rapidly. In contrast, all of the good glass formers—cinnarizine, itraconazole and ketoconazole—can supersaturate on their own. However, the maximum achievable concentration of the GFA class 3 drugs was unaffected by the presence of the tested polymers.

Author Contributions: Conceptualization, H.G., E.L., K.L., A.M., T.R.; Methodology, H.G., E.L., K.L., A.M., T.R.; Formal Analysis, L.I.B., T.R.; Investigation, L.I.B.; Writing-Original Draft Preparation, L.I.B., T.R.; Writing-Review & Editing, H.G., E.L., K.L., A.M.; Visualization, L.I.B. Funding: This work received financial support from Actelion Pharmaceuticals Ltd. and Idorsia Pharmaceuticals Ltd. Acknowledgments: We would like to thank Elise Jacob and Markus von Raumer from Idorsia Pharmaceuticals Ltd. for assistance and valuable discussions during this study. Furthermore, we would like to thank Rassul Hussain Ali Al Salman from the Department of Pharmacy at the University of Copenhagen for providing experimental data for supersaturation of cinnarizine. Conﬂicts of Interest: The authors declare no conﬂict of interest. E.L. is working in Idorsia Pharmaceuticals Ltd. since June 2017. The fund had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the result.

Appendix A

Table A1. Applied cooling rates during melt quenching to determine GFA class.

Compound Applied Cooling Rates (K/min) Naproxen 750, 20 Phenytoin 750, 20 Probenecid 750, 20 Cinnarizine 750, 20, 5, 1, 0.5 Itraconazole 750, 20, 5, 1, 0.5 Ketoconazole 750, 20, 5, 1, 0.5

Appendix B

Table A2. Probe tip lengths used in supersaturation studies.

Drug Probe Tip Length (mm) Naproxen 1 +0.05% HPMCAS-L 1 +0.50% HPMCAS-L 1 +0.05% PVPVA64 1 +0.50% PVPVA64 1 Phenytoin 1 +0.05% HPMCAS-L 1 +0.50% HPMCAS-L 1 +0.05% PVPVA64 1 +0.50% PVPVA64 1 Pharmaceutics 2018, 10, 164 12 of 14

Table A2. Cont.

Drug Probe Tip Length (mm) Probenecid 1 +0.05% HPMCAS-L 1 +0.50% HPMCAS-L 1 +0.05% PVPVA64 1 +0.50% PVPVA64 1 Cinnarizine 1 +0.05% HPMCAS-L 1 +0.50% HPMCAS-L 1 +0.05% PVPVA64 1 +0.50% PVPVA64 1 Itraconazole 5 +0.05% HPMCAS-L 5 +0.50% HPMCAS-L 5 +0.05% PVPVA64 5 +0.50% PVPVA64 5 Ketoconazole 2 +0.05% HPMCAS-L 2 +0.50% HPMCAS-L 2 +0.05% PVPVA64 2 +0.50% PVPVA64 2

Appendix C

Table A3. Solubility of drugs in fasted state simulated intestinal ﬂuid (FaSSIF) in absence and presence of either hypromellose acetate succinate L-grade (HPMCAS-L) or vinylpyrrolidine-vinyl acetate copolymer (PVPVA64) together with ﬁnal pH values of the respective media.

Naproxen Phenytoin Probenecid Cinnarizine Itraconazole Ketoconazole Medium (ug/mL) (µg/mL) (µg/mL) (µg/mL) (µg/mL) (µg/mL) 2412.0 ± 96.5 4.7 ± 0.9 2028.3 ± 79.3 20.7 ± 1.4 0.5 ± 0.1 17.6 ± 2.6 FaSSIF pH (6.0) pH (6.4) pH (6.7) pH (6.4) pH (6.4) pH (6.5) 2603.4 ± 768.5 ± 14.1 26.1 ± 1.6 14.4 ± 0.1 0.2 ± 0.1 25.1 ± 2.3 +0.05% HPMCAS-L 126.6 pH (5.7) pH (6.4) pH (5.5) pH (6.4) pH (6.4) pH (6.3) 1488.3 ± 87.1 30.2 ± 3.0 2499.0 ± 96.1 31.3 ± 1.0 0.4 ± 0.1 62.0 ± 3.9 +0.50% HPMCAS-L pH (5.1) pH (6.4) pH (5.2) pH (5.8) pH (5.7) pH (5.6) 2440.1 ± 1970.6 ± 81.6 21.0 ± 1.4 12.8 ± 0.5 0.2 ± 0.1 32.8 ± 2.2 +0.05% PVPVA64 202.7 pH (6.0) pH (6.4) pH (6.0) pH (6.4) pH (6.4) pH (6.4) 2093.2 ± 64.8 30.1 ± 1.6 2299.0 ± 92.1 16.5 ± 0.6 0.3 ± 0. 47.8 ± 2.0 +0.50% PVPVA64 pH (5.8) pH (6.4) pH (5.8) pH (6.4) pH (6.4) pH (6.4)

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