United States Patent (19) 11 Patent Number: 4,762,851 Alexander et al. (45) Date of Patent: Aug. 9, 1988

54 PYROGLUTAMIC ACID ESTERS USED AS (56) References Cited DERMAL PENETRATION ENHANCERS FOR DRUGS U.S. PATENT DOCUMENTS 4,540,572 9/1985 Seth ...... 424/81 75) Inventors: Jose Alexander; Takeru Higuchi, 4,555,524 1/1985 Gruber et al...... 514/947 both of Lawrence, Kans. 4,670,524 6/1987 Kamishita . OTHER PUBLICATIONS 73 Assignee: Merck & Co., Inc., Rahway, N.J. Chem. Abst, 104 (1986)-1161.11g, refers to Japanese Pat., Oct. 28, 1985. (21) Appl. No.: 802,907 Primary Examiner-Stanley J. Friedman Attorney, Agent, or Firm-Manfred Polk; Michael C. 22 Filed: Nov. 29, 1985 Sudol 57 ABSTRACT 51 Int. Cl." ...... A61K 31/19; A61K 31/20; The invention relates to pyroglutamic acid esters used A61K 31/40 as dermal penetration enhancers for therapeutic agents 52 U.S. C...... 514/420; 514/557; having poor skin permeation. 514/560 58) Field of Search ...... 514/420, 557, 570 8 Claims, No Drawings 4,762,851 1. 2 inducing undesirable physiological action by abrupt PYROGLUTAMIC ACID ESTERS USED AS increase in concentration in vivo. DERMAL PENETRATION ENHANCERS FOR But most drugs are not absorbed in sufficient concen DRUGS tration through the skin to exhibit pharmacological effect. This is because skin is an effective barrier to BACKGROUND OF THE INVENTION penetration. The outer layer of the epidermis, called the The invention relates to novel compositions and stratum corneum, offers the maximum resistance to methods for enhancing permeation of topically adminis penetration, whereas the lowerlayers are relatively per tered drugs by incorporating therein pyroglutamic acid meable. For proper treatment of dermal conditions, it is esters as dermal penetration enhancing agents. 10 important that the active agent penetrate the stratum Transdermal drug delivery to achieve systemic effect corneum where it is retained. From this reservoir in the is an area of much current interest and activity. While outer layer, the therapeutic agent could be slowly re the cutaneous route of input is advantageous in many leased and penetrates the underlying areas where it respects such as ease of use, better patient compliance, 15 could exhibit its therapeutic or cosmetic effect. When decreased first pass metabolism etc., the excellent bar dermatological agents such as sunscreens, which pro rier nature of the skin has so far limited the drugs con tect the underlying tissue from external factors (ultravi sidered suitable for transdermal delivery to very few. olet rays) are used, maximum retention in the stratum corneum is essential. On the other hand, the relative The use of adjunctive chemicals known as skin penetra permeability of the layers of the epidermis below the tion enhancers widens the scope of transdermal drug 20 stratum corneum can also allow access to the systemic delivery. Such use involves controlled impairment of circulation; indeed, it is necessary for the therapeutic the skin's protective layer, the stratum corneum. Ide agent to penetrate the stratum corneum in order to ally, no elements of the skin other than this horny layer provide systemic therapeutic effect from the trans should be involved in such a drug delivery approach, dermal route. because participation of any living tissue could result in 25 cellular insult and lead to an irritant or allergic re DESCRIPTION OF THE PRIOR ART sponse. So an ideal penetration enhancer is one which speeds the permeation of the drug through the stratum Many investigators have turned to various enhancing corneum, without itself crossing this barrier, or if it agents such as dimethylsulfoxide, dimethylformamide crosses, undergoes fast metabolic destruction and/or 30 and various other aliphatic and aromatic amides, cyclic detoxification in the viable area of the skin. This inven amides (Akerman et al., Pharmacol. et Toxicol. 1979, tion deals with an analagous series of penetration en 45, 58), methyldecylsulfoxide (U.S. Pat. No. 3,527,864), hancers of the latter type. dimethylacetamide (U.S. Pat. No. 3,472,931) and the It is well known that a number of therapeutically like to deliver topically active agents more efficiently 35 through the skin, as well as to enhance the absorption of active agents, such as B-blockers, antihypertensives, systemically active therapeutic agents through the skin antiarrhythmics, antianginal agents, vasodilators, antie into general circulation. U.S. Pat. No. 3,989,816 dis metics, antibacterials, antifungals, corticosteroids, an closes that 1-substituted azacyclopetane-2-one deriva tiinflammatories and the like when administered to tives enhance penetration of a physiologically active warm-blooded animals by a number of various routes agent through the skin. U.S. Pat. No. 3,920,814 discloses such as by intravenous infusion, intramuscular injection, that the antibacterial activity of antibiotics such as peni oral, rectal or buccal routes, enter the general circula cillins and cephelosporins is potentiated by coadminis tion and produce the appropriate systemic therapeutic tration with pyrrollidone carboxylic acid or a salt deriv effect. It is also known that the aforementioned methods ative thereof. The reference directs itself to oral and of administration have certain disadvantages. For exam 45 intravenous forms of administration. U.S. Pat. No. ple, the intravenous and intramuscular routes are not 3,836,665 discloses a topical dermatological composi only painful for the patient, but also must be performed tions for cosmetic sebacious gland excretion-inhibiting by a trained individual. Buccal and rectal administration treatment or therapeutic antiphlogistic treatment of the often produce discomfort and annoyances for the pa skin consisting of an inert dermatological carrier and tient. Oral administration, although generally accept 50 alkyl esters of 5-pyrolidone-2-carboxylic acid. Finally, able for the patient, often does not deliver much of the European Patent Application No. 0123948A1 (1984) therapeutic agent to systemic circulation. This dimin claims glycerol pyroglutamates wherein one or both of ished drug delivery is usually attributed to poor absorp the glycerol hydroxyls etherified with alkyl or alkenyl tion from the gastrointestinal tract and/or to degrada groups as shown below as penetration enhancers: tion of the agent by the acidic medium of the stomach, by the enzymes in the gastrointestinal tract and sur 55 rounding tissue, or by the rapid metabolism by enzymes of the liver through which the drug must pass before it enters the systemic circulation. For example, drugs such as anti-bacterials, narcotic analgesics, 3-blockers and 60 O T co-Chih- CHOR2 others require relatively high doses when given orally OR due to the remarkable liver metabolism encountered. Effective delivery of such drugs through the skin would The similarity of the side chain in the above mentioned require much lower doses because the so-called "first application to nonionic surfactants and the use of such pass' metabolism would be avoided. Additionally, the 65 agents in enhancing the penetration of medication topical application of the drug has the advantage that through mucous membranes of warm blooded animals their pharmacological action is exhibited gradually over has been studied heretofore. In fact, Japanese Patent an extended period of time avoiding the possibility of Application No. 2961/1984 teaches that pyroglutamic 4,762,851 3 acid monoglycerides have surface active action and are effective emulsifiers, penetrants, detergents, spreaders and antistatic agents and are considered to have skin protecting acion. However, our discovery that simple a alkyl and alkenyl esters of pyroglutamic acid which do O N CO2H not have the non-ionic-surfactant-like side chain are skin penetration enhancers is unanticipated and unobvi H ous. In fact, our compounds have certain advantages wherein R is a straight or branched chain alkyl (C5-C20) over the others: (1) the alkyl and alkenyl esters do not 10 such as pentyl, heptyl, octyl, decyl, dodecyl, tetradecyl, show skin irritation on occlusive application for 24 hexadecyl, octadecyl, stearyl, eicosyl and the like; alke hours, whereas the glyceride esters show erythema on nyl (C5-C20) with 1-6 double bonds such as pentenyl, application for 24 hours; (2) the alcohols derived from octenyl, decenyl, dodecenyl, farnesyl, oleyl and the hydrolysis of our compounds are non-toxic and are like; hydroxylalkyl (C5-C20) with 1 to 3 hydroxy endogenous substances or metabolic precursors of fatty 15 groups such as hydroxypentyl, hydroxydecyl, hydrox acids whereas some glycerol ethers are known to be yhexadecyl, dihydroxyoctadecyl and the like; ketoalkyl potent mutagens (J. Am. Chem. Soc. 1982, 104, 6149). (C5-C20) such as 2-ketapentyl, ketododecyl, ketohex SUMMARY OF THE INVENTION adecyl and the like; unsaturated hydroxyalkyl (C5-C20) such as hydroxyoctenyl, hydroxydodecenyl, hydrox This invention relates to pyroglutamic acid ester used 20 yhexadecenyl and the like; carboxyalkyl (C5-C20) such as dermal penetration enhancers for thereapeutic agents as co-carboxyoctyl, co-carboxyhexadecyl and the like or having poor skin permeation. alkoxycarbonylalkyl (C5-C20) such as ethoxycarbonyl Accordingly, it is an object of the invention to pro hexyl, ethoxycaronyldodecyl and the like. vide a novel concept in skin penetration enhanced drug The pyroglutamic esters of the invention are known delivery, namely, the use of penetration enhancers that 25 compounds and processes for their preparation are undergo metabolic destruction when they cross the known in the art. stratum corneum into the viable area of the skin tissue. In accord with the foregoing objects, the invention A further object of the invention is to provide a novel provides a novel composition of matter for topical ap class of skin penetration enhancers which after achiev plication comprising at least one drug or therapeutic ing their function of promoting the permeation of a 30 agent and an ester of pyro-glutamic acid and further drug or medicament through the stratum corneum, comprises, if desired, a non-toxic topical pharmaceuti undergo fast metabolic breakdown into nontoxic meta cally acceptable carrier. The therapeutic agent is pres bolic products as soon as they reach the live area of the ent in a biologically effective amount, i.e., in an amount skin. sufficient to produce the desired biological effect. Thus, Another object of the present invention is to provide 35 when the therapeutic agent is a dermatological agent, it a novel class of penetration enhancers, which will en is utilized in a dermally effective amount, i.e., in an hance the dermal absorption of therapeutic or cosmetic amount sufficient to evoke the desired dermal effect agents, such enhancers being capable of improving de (which may be cosmetic or therapeutic in nature). On livery through the skin and into the general circulation the other hand, when the therapeutic agent is systemi of systemically active drugs. cally active and introduction of the agent into the gen Another object is to provide penetration enhancing eral circulation is desired then the amount is employed agents devoid of toxic side effects by virtue of fast meta in a systemically effective amount, i.e., in an amount bolic breakdown as they come into contact with living sufficient to produce the desired systemic response. tissue. 45 Pyroglutamate ester is employed in such compositions Still another object of this invention is to provide a in an amount sufficient to enhance skin permeation of class of penetration enhancing agents whose breakdown the therapeutic agent. products are endogenous, or precursors of endogenous Various active agents provide beneficial effects when substances which can be metabolized through normal administered to patients. Such agents which can be SO made more useful by enhancing its absorption in accor pathways available in the body. dance with this invention, are exemplified by, but not Yet another object of the invention is to provide limited to, the following classes of agents: novel compositions utilizing the aforementioned en (A) Antiarrythmic: Bucainide, diisopyramide, encai hancing agents for toptical application and novel meth nide, tocainide, verapamil, and the like; ods of enhancing the skin penetration of therapeutic 55 (B) Antihypertensive such as clonidine, enalapril, agents. hydralazine, prazosin, a-methyldopa and the like; These and other objects and advantages of the inven (C) Antivirals such as acyclovir, cytarabine, envirox tion will become apparent from the following descrip ime, floxuridine, ribavarin, vidarabine, idoxuridine, tri tion. fluridine and the like; 60 (D) g-Blockers such as propranolol, bupranolol, DESCRIPTION OF THE INVENTION metoprolol, atenolol, pindolol, betaxalol, tinolol, sota The invention is concerned with novel compositions lol, alprenolol, nadolol, oxprenolol and the like; and methods for enhancing the permeation of topically (E) Diuretics such as aldactone, hydrochlorothiazide, administered drugs by incorporating therein a pyro ticrynafen and the like; glutamic acid ester as a dermal penetration enhancing 65 (F) Non-steroidal antiinflammatory agents, such as agent for said drugs. The dermal penetration enhancing indomethacin, naproxen, fenoprofen, ibuprofen, alcol agents are described according to the general structural fenac, phenylbutazone, mefenamic acid, diflunisal, formula below: sulindac, desoxysulindac, aspirin, salicylamide, salicylic 4,762,851 5 6 acid, oxyphenbutazone, apazone, cintazone, flufenamic acid, meclofenamic acid, flunixin, dimefadane, indoxole, EXAMPLE 1. intrazole, mimbane hydrochloride, paranylene hydro Decyl Pyroglutamate chloride, tetrydamine, benzindopyrine hydrochloride, fluprofen, ibufenac, ketoprofen, naproxol, fenbufen, To an ice cold suspension of pyroglutamic acid (1.3 g) cinchophen, diflumidon sodium, fenamole, flutiazin, and n-decanol (1.6 g) in dichloromethane (50 ml), dicy metazamide, letimide hydrochloride, nexeridine hydro clohexylcarbodiimide (2.1 g) and 4-dimethylaminopyri chloride, octazamide, molinazole neocinchophen, nima dine (0.1 g) were added. After stirring at ice bath tem zole, proxazole citrate, tesicam, tesimide, tolmetin, perature for 2 hours, the cooling bath was removed and tramadol, triflumidate and the like; 10 the mixture was stirred at room temperature overnight. (F) Steroidal antiinflammatory agents, i.e., cortico The dichloromethane was evaporated off. The residue steroids, such as hydrocortisone, hydrocortisone 17-val was taken in ether and filtered. The filtrate was washed erate, hydrocortisone 17-butyrate, hydrocortisone with 1N HCl, water, aqueous bicarbonate and water. It 21-acetate, betamethasone valerate, triancinolone was then dried over Na2SO4 and evaporated. The resi 15 due weighed 2.75g. It was chromatographed oversilica acetonide, fluocinonide, desonide, fluocinolone aceto gel. The pure decyl ester was eluted with ethylacetate nide, dexamethasone, prednisolone, haloprednone, cor chloroform (1:4), 2.3 g m.p. 34"-35". tisone acetate, cortisone cyclopentylpropionate, corto n-Dodecyl, farnesyl an oleyl pyroglutamates were doxone, flucetonide, fludrocortisone acetate, fluran drenolone acetonide, medrysone, amcinafal, amcina prepared similarly and purified by chromatography. fide, betamethasone, betamethasone benzoate, chloro 20 EXAMPLE 2 prednisone acetate, clocortolone acetate, descinolone Rat plasma hydrolysis of decyl pyroglutamate acetonide, desoximetasone, dichlorisone acetate, diflu prednate, flucloronide, flumethasone, flunisolide ace Freshly prepared rat plasma (2 ml) was mixed with tate, fluocortolone, fluorometholone, fluperolone ace decyl pyroglutamate (0.6 mg) and was maintained at 37 tate, fluprednisolone, fluprednisolone valerate, mepred 25 C. Aliquots were removed at different time intervals nisone, methyl prednisolone, paramethasone acetate, and vortexed with heptane (1 ml) containing dodecanol prednisolamate, prednisone, prednival, triamcinolone, as an internal standard. The decanol produced by enzy triamcinolone hexacetonide, cortivazol, formocortal, matic hydrolysis was assayed by gas chromatography nivazol and the like; 30 on a 6X2 mm (id) column packed with OV-101 (me (G) Muscle relaxants such as theophylline, cycloben thylsilicone) on gas chron Q (100-120 mesh), pro Zaprine, aminophylline, diphylline, oxtriphylline, amb grammed from 125 to 175 C. Decyl pyroglutamate uphylline, fenethylline, guathylline, pentoxyfylline, generated decanol with a t of 18 min. by enzymatic xanthinol niacinate, theophylline glycinate, glucopyl hydrolysis. line and the like. 35 EXAMPLE 3 (H) Polypeptides such as cyclo-(N-Me-Ala-Tyr-D- Trp-Lys-Val-Phe)acetate, somatostatin, insulin, gastrin, Skin Irritation Study of Pyroglumate Esters caerulein, cholecystokinin and the like; Fuzzy rats (Temple University) 150 to 200 g were (I) Coronary Vasodilators such as, diltiazem, dipyrid used to study the dermal irritancy as the neat com amole, erythritol tetranitrate, nifedipine and the like; pounds. Test preparations (50 mg) were applied to cir and cular gauze pads 1 mm thick and 16 mm in diameter, (J) Prostanoids such as rioprostil, viprostil, doxa and affixed to the animals' dorsal surface with occlusive prost, enisoprost, enprostil and the like. adhesive film (Adhesive Plaster for Patch Test, The enhancement of drug absorption in accordance Kanebo, Ltd., Osaka, Japan). The occlusive dressings with this invention is not by any means limited to the 45 were removed after 3 or 7 days. Treated skin areas were above drugs, but are in general applicable to other then evaluated according to a modified Draize scoring classes of drugs such as analgesics, anabolics, andro method, and the irritation index was evaluated for each gens, anorexics, adrenergics, antiadrenergics, antialler test site. The first or "primary irritation index' (PII) gics, antibacterials, anticholinergics, antidepressants, was an average value reflecting irritation both immedi antidiabetics, antifungal agents, antihypertensives, anti 50 ately after dressing removal, and 72 hours later. The neoplastics, antipsychotics, sedatives, cardiovascular "secondary irritation index'(SII) was determined 7 agents, antiulcer agents, anticoagulants, anthelmintics days after dressing removal. The maximum possible PII and the like. or SII was 8 with a total possible score of 4erythema, The amount of drug varies over a wide range but in and a total possible score of 4 for edema. A PII or SII general the therapeutically effective unit dosage 55 less than or equal to 2 indicated a mild irritant, a PII or amount of the selected drug depends on that amount SII greater than 2 but less than or equal to 6 indicated a known in the art to obtain the desired results. moderate irritant, and a PII greater than 6 indicated a Generally, the amount of enhancing agent employed severe irritant as shown in Table 1 below: in the practice of this invention ranges from 0.75 mg to 60 TABLE 1. 1 g in each unit dose. The weight percentage of enhanc Irritation data for pyroglutamate esters ing agent in the total combination of drug plus agent is Primary Irritation Secondary . 5-99% with a preferred ratio of enhancing agent in the Index Irritation Index total combination of agent plus drug being 10-40%. Sample (50 mg applied To-T12hrs' at 7 days The following examples illustrate preparation of vari 65 over 2 cm surface) 3 DAY occlusion 3 DAY occlusion ous compositions of the invention. The examples should Decyl pyroglutamate 0.9 + 1.1 (4)** 0. Oleyl pyroglutamate 0.1 - 0.3 (4) O be construed as illustrations rather than limitations Dodecyl pyroglutamate 0 (2) O thereof. Farnesyl pyroglutamate 0 (2) O 4,762,851 8 TABLE 1-continued TABLE III Irritation data for pyroglutamate esters Penetration Enhancement Using Primary Irritation Secondary Dodecyl pyroglutamate Index Irritation Index 5 weight ratio of flux of drug Sample (50 mg applied To-T2hrs at 7 days Drug enhancer/drug plg/cm/hr over 2 cm surface) 3 DAY occlusion 3 DAY occlusion Hydrocortisone O Not detectable 15 0.338 Azone 4.0 - 1.9 (5) O Propanolol O 3.68 To is time at which occlusive application is removed. 15 7.4 Irritation index de Sid (n). 10 What is claimed is: EXAMPLE 4 1. A method of enhancing the rate of dermal absorp tion of a composition which comprises topically admin Permeation enhancement using pyroglutamate esters istering to a patient a therapeutically effective dosage In the examples given below, the permeation en amount of said composition comprising a non-steroidal hancement was determined using an in vitro diffusion 15 anti-inflammatory drug selected from the group consist cell procedure. The molts of adult Elaphe obsolete (black ing of indomethacin, naproxen, fenoprofen, ibuprofen, rat snake) was used as the model for stratum corneum alcolfenac, diflunisal, sulindac, desoxysulindac, flu membrane (R. Ibuki, Ph.D. Thesis, University of Kan profen, ketoprofen, naproxol, and fenbufen and a pyro sas, 1985). The shed snake skin has great similarties to glutamic acid ester absorption enhancing agent of the human skin in terms of thickness, composition of con 20 formula: stituents and structure and has been proposed as the most suitable model for human stratum corneum for permeability studies. Glass diffusion cells consisting of a donor and recep tor cells separated by the shed snake skin membrane 25 were assembled using spherical O-ring joints held to gether by spring clamps. The exposed membrane sur face area of the diffusion cell measured 1.8 cm2. Before wherein R is a straight or branched chain alkyl being mounted in the diffusion cell approximately 25 (C5-C20), alkenyl (C5-C20) with 1-6 double bonds, hy mg of an ointment containing the therapeutic agent and 30 droxyalkyl C5-C20) with 1-3 hydroxy groups, ketoalkyl the penetration enhancer was carefully applied to the (C5-C20), unsaturated hydroxyalkyl (C5-C20), carboxy membrane and was spread over the desired area. The alkyl C5-C20) or alkoxycarbonylalkyl C5-C20). receptor side was filled with approximately 8.5 ml of 2. The method of claim 1, wherein said drug is indo buffer solution consisting of 1.5x10-1M NaCl, 35 methacin, ibuprofen or naproxen and said enhancing 5X10-4M NaH2PO4 and 2.0x10-4M Na2HPO4 ad agent is represented when R is alkyl or alkenyl. 3. The method of claim 2, wherein said drug is indo justed to pH 7.2 with NaOH. methacin and R is alkenyl. The diffusion cell was immersed vertically in a water 4. A pharmaceutical composition for enhancing der bath maintained at 32-1 C. The receptor cell was mal absorption of a topically administered non-steroidal stirred constantly with a magnetic stirrer. To determine 40 anti-inflammatory drug selected from the group consist the amount of compound penetrated through the snake ing of indomethacin, naproxen, fenoprofen, ibuprofen, skin membrane from the upper chamber, 0.2 ml samples alcofenac, diflunisal, sulindac, desoxysulindac, flu were withdrawn at varying intervals from the receptor profen, ketoprofen, naproxol, and fenbufen, comprising chamber using a syringe. An equal amount of fresh a therapeutically effective dosage amount of said drug buffer was replenished during sampling. The concentra 45 and a pyroglutamic acid ester enhancing agent of the tion of drug penetrated in each diffusion cell was mea formula: sured using high pressure liquid chromatography. The results reported for each experiment are the average values from 5 replicate diffusion cells. The ointments used for the experiments contained 50 varying concentrations of the drug and penetration enhancing agent. The drug was dispersed in the en hancer and this was then mixed with white petrolatum USP using a vortex mixer around 55° C. The ointments were kept in a water bath at 32"-1" C. for 1 day before 55 wherein R is a straight or branched chain alkyl use in vitro studies. See Tables II and III below for the (C5-C20), alkenyl (C5-C20) with 1-6 double bonds, hy droxyalkyl (C5-C20) with 1-3 hydroxy groups, ketoa results of penetration enhancement effects. kyl (C5-C20), unsaturated hydroxyalkyl (C5-C20), car TABLE II boxyalkyl (C5-C20) or alkoxycarbonylalkyl (C5-C20). Penetration Enhancement of Indonethacin 60 5. The composition of claim 4, wherein said drug is weight ratio of flux of indomethacin, ibuprofen or naproxen and said enhanc enhancera indomethacin ing agent is represented when R is alkenyl. skin penetration enhancer indomethacin g/cmhr 6. The composition of claim 5, wherein R is decenyl, n-Decyl pyroglutamate 15.0 0.477 farnesyl or oleyi. n-Dodecyl pyroglutamate 15.0 0.630 7. The composition of claim 6, wherein said drug is Farnesyl pyroglutamate 15,0 0.317 65 indomethacin and R is oleyl. Oleyl pyroglutamate 15.0 0.450 8. The composition of claim 4 further comprising None non-detectable pharmaceutically acceptacle excepients.