ORIGINAL ARTICLES Department of Pharmaceutical Technology, Faculty of Pharmacy, Gazi University, Ankara, Turkey The effects of surfactants on the solubility and dissolution profiles of a poorly water-soluble basic drug, carvedilol T. Incecayir Received May 3, 2015, accepted July 14, 2015 Tuba Incecayir, Ph.D., Gazi University, Faculty of Pharmacy, Department of Pharmaceutical Technology, Etiler 06330, Ankara, Turkey [email protected] Pharmazie 70: 784–790 (2015) doi: 10.1691/ph.2015.5081 This study investigated the most suitable surfactant medium for the dissolution testing of a poorly soluble basic drug, namely, carvedilol reflecting the in vivo behavior. Sodium lauryl sulfate (SLS), hexade- cyltrimethylammonium bromide (CTAB) and polysorbate 80 were used as anionic, cationic and nonionic surfactants, respectively. Saturation solubilities of carvedilol were determined in the presence of SLS, CTAB and polysorbate 80 (0.5, 1 and 2% (w/v)) at pH 1.2 and 6.8. Dissolution behaviors of the commercial tablets were studied using USP apparatus II in pH 1.2, 4.5 and 6.8 buffers and pH 6.8 dissolution media with 0.5% (w/v) SLS, polysorbate 80 and CTAB. Polysorbate 80 enhanced the solubility of carvedilol irrespective of pH, while SLS and CTAB exhibited larger solubilization effect than polysorbate 80 depending on pH and the ionic nature of the surfactant. Based on in vitro dissolution profile similarity, pH 6.8 dissolution medium with 0.5% (w/v) polysorbate 80 was found to be the most biorelevant medium, which probably reflects the bioequivalence of test products to the reference product of carvedilol. 1. Introduction relation between in vitro dissolution and in vivo performance for BCS Class II drugs at the present time (Shah and Amidon Since solubility and permeability interactions and their impact 2014; Tubic-Grozdanis et al. 2008). Therefore, it is a chal- on intestinal drug absorption were most prominently described lenge to develop an appropriate in vitro dissolution test for BCS by the Biopharmaceutics Classification System (BCS), it has Class II drug products for quality control (QC) purposes and continued to attract strong interest from pharmaceutical indus- drug product development, as well as for the establishment of try and drug regulatory authorities worldwide (Amidon et al. IVIVC or biorelevance. For weakly acidic and basic Class II 1995; Shah and Amidon 2014). BCS is a scientific framework for drugs, the pH and composition of the dissolution medium are classifying drugs into four groups according to their aqueous sol- of great impact on the dissolution process. In such cases, sur- ubility and intestinal permeability: class I (high solubility − high factants may be added to dissolution media to enhance drug permeability), class II (low solubility − high permeability), class solubility and dissolution and provide sink conditions due to III (high solubility − low permeability) and class IV (low solu- the physiological relevance of the synthetic surfactants (Ami- bility − low permeability) (Amidon et al. 1995). Currently, the don et al. 1995; Park and Choi 2006; Sheng et al. 2006; Shah US Food and Drug Administration (FDA) has promoted the et al. 1989). BCS as a scientific approach to permit a waiver of in vivo The aim of the present study was to investigate the effects bioequivalance (BE) testing for immediate release (IR) solid of medium pH and different types of surfactants (anionic, dosage forms for Class I drugs based on in vitro dissolution cationic and nonionic) on the solubility of carvedilol and the of a drug product, while the 2010 European Medicine Agency dissolution of its products and identify the most suitable sur- (EMA) BE Guideline has further extended its discussion of factant medium for the dissolution testing reflecting in vivo biowaivers to Class III drugs with very rapid dissolution (FDA dissolution of the drug. Being a BCS II weak base (Wu Guidance 2000; EMA Guideline 2010). Current FDA and EMA and Benet 2005), carvedilol (1-(9H-carbazol-4-yloxy)-3-[2-(2- regulations do not allow biowaiving for BCS Class II drugs, how- methoxyphenoxy)ethylamino]propan-2-ol) was chosen as the ever World Health Organization (WHO) considers biowaiving model drug for the present study. Carvedilol is a nonselective ␤- of certain weak acids belonging to BCS Class II (diclofenac, blocking agent with ␣1-adrenergic antagonist activity (Fig. 1). ibuprofen and ketoprofen) which are exhibiting poor solubility It has been clinically used in the treatment of mild to moderate at acidic pH but high solubility at pH 6.8 (Chuasuwan et al. congestive heart failure and hypertension (Packer et al. 1996; 2009; Potthast et al. 2005; Shohin et al. 2012). For BCS Class Nägele et al. 2000; Rizos and Elisaf 2014). Carvedilol is rapidly II drugs, absorption is rate limited by in vivo dissolution, and and extensively absorbed with peak plasma concentration occur- possible in vitro-in vivo correlation (IVIVC) can be established ring 1 to 2 h after the administration and elimination half-life to predict in vivo performance of a BCS Class II drug prod- of 4 to 7 h (Morgan 1994). However, it is extensively metab- uct (Yu et al. 2002). However, it is clear that more research olized resulting in approximately 24% absolute bioavailability is needed to provide a mechanistic understanding of the cor- (Neugebauer et al. 1987). 784 Pharmazie 70 (2015) ORIGINAL ARTICLES Fig. 1: Chemical structure of carvedilol. ◦ Fig. 2: Solubility of carvedilol (␮g/mL) in buffers of different pHs at 37 C (n = 3). Fig. 3: Effects of surfactants (SLS, CTAB and polysorbate 80) on saturation solubility (CS) of carvedilol in pH 1.2 hydrochloric acid and pH 6.8 In the present study, sodium lauryl sulfate (SLS), hexade- phosphate buffers (n = 3). cyltrimethylammonium bromide (CTAB) and polysorbate 80 were used as the anionic, cationic and nonionic surfactants, respectively. The solubility of carvedilol in different buffers and 2.2. Effects of surfactants on solubility surfactant media within the physiological pH range was mea- The effects of surfactants (SLS, CTAB and polysorbate 80) on sured. In vitro dissolution tests were performed in various media the saturation solubility of carvedilol at pH 1.2 and 6.8 are pre- to compare the dissolution profiles of the bioequivalent products sented in Fig. 3. The solubility of carvedilol increased gradually of carvedilol. with the increased concentrations of all surfactants (r2 = 0.928- 0.999). SLS and CTAB exhibited larger solubilization effect than polysorbate 80 at both pH 1.2 and 6.8. 0.5-2% (w/v) SLS 2. Investigations and results enhanced the solubility of carvedilol 2.5-70 and 8.9-192 fold 2.1. pH dependent solubility at pH 1.2 and 6.8, respectively. Upon addition of 0.5-2% (w/v) CTAB, a dramatic increase in the solubility of carvedilol (58- Saturation solubility values of carvedilol at different pH values 235 fold) was observed at pH 6.8, while the effect at pH 1.2 are presented in Fig. 2. Calcd. dose numbers (DO) and rela- was much smaller than that at pH 6.8 (7.3-18 fold). The highest tive sink conditions (CS/CD) in the buffers of different pHs are concentration of polysorbate 80 (2% (w/v)) enhanced the drug presented in Table 1. Solubility of carvedilol increased signifi- solubility only 10 and 27 fold at pH 1.2 and 6.8, respectively. In cantly as pH increased from 1.2 to 4.5, and it decreased as pH the presence of the same polysorbate 80 concentrations, solubil- further increased, giving low solubility values at pH 6.8 and 7.4. ity values of carvedilol were similar at pH 1.2 and 6.8. Relative The solubility values of carvedilol determined in pH 4.5 and 5.5 sink conditions of carvedilol in the presence of different con- acetate buffers were 75 and 8 fold higher than that in pH 1.2 ◦ centrations of surfactants at pH 1.2 and 6.8 are summarized in hydrochloric acid buffer at 37 C, respectively. Table 2. The ratio of saturation solubility to drug concentration calculated by dividing the dose by 900 mL dissolution medium (CS/CD) represents the closeness to the sink condition. CS/CD Table 1: Dose numbers (DO) and relative sink conditions values greater than three are considered to provide sink condi- (CS/CD) of carvedilol in buffers tion (USP 2007). Therefore, 0.5% (w/v) surfactant (SLS, CTAB or polysorbate 80) was used in dissolution medium (pH 6.8) for a b c Medium DO CS /CD the dissolution of 25 mg carvedilol tablets. pH 1.2 hydrochloric acid buffer 1.5 2.42 pH 4.5 acetate buffer 0.02 181 2.3. Surfactant mediated dissolution pH 5.5 acetate buffer 0.19 19.3 pH 6.8 phosphate buffer 4.4 0.815 Based on the CS/CD values (2.42 and 0.815 at pHs 1.2 and 6.8, pH 7.4 phosphate buffer 14 0.252 respectively), sink conditions were not met at pH 1.2 and 6.8 media. However, it is recommended to perform the dissolution adose number; bsaturation solubility of carvedilol; ctheoretical concentration of drug assuming of carvedilol tablets using apparatus II (paddle) in 900 mL pH 1.2 complete dissolution of 25 mg carvedilol tablet in 900 mL dissolution medium. simulated gastric fluid (SGF) without enzyme at 50 rpm (FDA Pharmazie 70 (2015) 785 ORIGINAL ARTICLES Table 2: Relative sink conditions (CS/CD) of carvedilol in surfactant media a b CS /CD SLSc concentration (% w/v) CTABd concentration (% w/v) Polysorbate 80e concentration (% w/v) pH 0.5 1 2 0.5 1 2 0.5 1 2 1.2 2.42 5.94 50.9 170 17.6 26.1 44.7 7.46 11.7 23.6 6.8 0.815 7.23 58.6 156 46.9 91.3 191 8.51 13.2 21.9 asaturation solubility of carvedilol; btheoretical concentration of drug assuming complete dissolution of 25 mg carvedilol tablet in 900 mL dissolution medium; csodium lauryl sulfate; dhexadecyltrimethyl ammonium bromide; epolyoxyethylenes orbitan monooleate.