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1 As appeared in Tablets & Capsules January 14 A rapid vehicle-screening approach for formulating a low-solubility compound into liquid-filled capsules formulation Amol Kheur, Anil Kane, Mohammad Aleem, and Maureen McLaughlin Patheon Pharmaceutical Development Services Kiran Kumar Tumbalam and Shivaprakash Poojary Formerly of Patheon For a drug product to exert its therapeutic effect, it must be soluble in an aqueous environment. This ensures that the active pharmaceutical ingredient (API) will provide sufficient concentration to induce gastrointestinal (GI) tract absorption. Hence, molecules with promising pharmacodynamics yet poor solubility may be rejected during the drug discovery stage. This article summarizes how an excipient-mixture approach can enhance the solubility, the in vitro dissolution, and the bioavailability profile of a low-solubility compound. As drug development costs continue to rise, it has become increasingly important for companies to assess early on whether a new molecular entity (NME) will succeed in clinical trials. Analyzing the structure of a new compound is an especially crucial step in the discovery stage for orally active drugs, as their solubility and permeability properties are two of the strongest predictors of whether Phase II (proof-of-concept) studies will commence [1]. Companies profile NMEs so they can incorporate certain desirable characteristics into the molecule; select lead compounds that are likely to survive in the pipeline;

2 and recognize development risks as soon as possible [2]. Key criteria in assessing an NME s development potential include economic factors, such as ease of manufacture and market size; pharmacological considerations, such as therapeutic ratio, toxicity, and how the compound interacts with other APIs; and physical characteristics, such as solubility [1]. Solubility, which refers to the concentration of a solute in a saturated solution at a defined temperature and pressure, is key to a drug product s efficiency [3]. For a drug product to exert its therapeutic effect, it must be soluble in an aqueous environment. This quality ensures that the API will dissolve in intestinal fluids and provide sufficient concentration to induce absorption in the GI tract [4]. The oral delivery of low-solubility drug products is associated with slow dissolution rates, low and variable bioavailability, and a higher potential for food effect [2]. Hence, API candidates with promising pharmacodynamics may be rejected as lead molecules due to poor solubility. Unfortunately, approximately percent of all NMEs exhibit this quality [5], meaning that they are classified as either Class II (low solubility, high permeability) or Class IV (low solubility, low permeability) in the Biopharmaceutics Classification System (BCS). Factors that cause poor solubility include high crystallinity and hydrophobicity [2]. The latter is a characteristic more commonly found in leads obtained via highthroughput screening (HTS) because those NMEs tend to have higher molecular weights than do leads acquired during the pre-hts era [6]. HTS allows for exponentially faster screening at a fraction of the cost of conventional techniques, and it has thus become a major paradigm of drug discovery [7]. As a result, new formulation strategies are required to achieve acceptable bioavailability. Liquid-filled hard capsules (LFHCs) offer a platform for managing the successful transition from a low-solubility, to-be-abandoned molecule to a potent bioactive drug product. The means to do so, however, are restricted by the API s physicochemical properties, which aside from poor water solubility may also include a low melting point (causing it to stick to tooling surfaces), a critical stability profile, and a short half-life [8]. Formulators can use a wide array of solubilizers, co-solvents, surfactants, and emulsifying agents to achieve favorable pharmacokinetics. For instance, an API s rate of release from hard capsules filled with semi-solid excipients can be controlled by using excipients with different hydrophilic-lipophilic balance (HLB) values, as demonstrated by an experiment in which the in vitro release rate of salicylic acid from a mixture of lipid excipients (Gelucire from Gattefossé) was found to be directly proportional to the HLB value of the composition of the fill material [9]. Generous use of any one excipient is limited, however, by permissible-daily-intake standards, individual solubilizing capacities, and potential interactions with the capsule wall: The fill material must not degrade or leak through the gelatin shell. So the challenge is to find a formulation approach that enables the judicious selection of excipients by type and use level. This article summarizes how an excipient-mixture approach was able to enhance the solubility, in vitro dissolution, and bioavailability profile of a low-solubility (.5 milligram per milliliter (mg/ml)) BCS Class II compound, thereby enabling researchers to establish a reasonable spread of prototype formulations in order to conduct in vivo studies in animals. Methodology Stage 1: Vehicle screening studies. In the first set of trials, the API was dissolved in a variety of excipients that were either liquid or semi-solid at ambient temperature, using an approximate API-to-excipient ratio of 1-to-9. The solutions were then visually evaluated for clarity and sonicated for 3 minutes to further agitate the particles. A clear solution was not achieved, however, indicating that none of the excipients adequately dissolved the API. Consequently, no further studies were conducted at ambient temperature. Subsequent trials involved dissolving the API in a variety of excipients at elevated temperatures (~65 C ±5 C) through the application of indirect heat (using a water bath and hot plate) accompanied by intermittent stirring. Some of the excipients were semi-solid at room temperature but melted at temperatures exceeding 55 C. An approximate API-to-excipient ratio of 1-to-9 also expressed as ~1.1 percent w/w API was again used. See Table 1 for a list of the excipients evaluated at higher temperatures. Based on initial solubility studies of the excipient preparations used to make self-emulsifying lipid formulations (SELFs), preparations 27C, 27D, 27F, and 27H were heated gradually from 65 to 115 C. It was observed that the API dissolved incrementally as the temperature increased. At temperatures higher than 65 C, however, some excipients degraded, so 65 C became the target temperature in further studies. Stage 2: A mixture approach to study solubility at elevated temperatures. Select excipients were mixed in various proportions (Table 2). The API was then dissolved in each mixture and each was assessed to gauge solubility improvement. Similar to the solubility process used for individual excipients, indirect heat was applied to melt the excipients and/or disperse the API. A temperature of approximately 65 C was maintained throughout the evaluation process, and the quantity of API used was gradually increased depending on the solubilization capacity of the mixture. Stage 3: Selection of an optimal mixture. Based on the literature and a visual evaluation of the API s solubility in various excipients and excipient mixtures, it was hypothesized that a combination of two or more select excipients (Imwitor 38, Gelucire 44/14, vitamin E TPGS, hydroxypropyl beta cyclodextrin, and propylene glycol) would yield a formulation with the desired in vitro dissolution profile and in vivo bioavailability characteristics. Among these five excipients, Gelucire 44/14 was con-

3 sidered a key ingredient for emulsification and potential bioavailability enhancement. Two SELF preparations (27F and 27H) were also selected to assess in vitro dissolution. Stage 4: Manufacture of prototype batches. Four excipient combinations (lots 1 through 4) were used to formulate LFHC prototypes (Table 3). These prototypes were manufactured with the required target dose in batches of 1,5 capsules, but the capsules were not banded and thus not completely sealed. The butylated hydroxyanisole (BHA) and butylated hydroxytoluene Table 1 Excipients evaluated at elevated temperature Gelucire 44/14 Crillet 1 HP Labrasol Plurol Oleique CC 497 Solutol HS 15 Cremophor RH 4 Propylene glycol PEG Peppermint oil Miglyol 81 PEG Labrafil M2125 Vitamin E TPGS Cremophor ELP Medium-chain triglycerides Schercemol TN Labrafac CC Polysorbate Macol LA 4 Gelucire 5/13 Transcutol Soybean oil Glycerin Sunflower oil Captex 355 Captex P Capmul MCM Capmul PG-8 Bio-Soft N25-7 Neobee M-5 Lauroglycol 9 Labrafac Hydro WL 1219 Labrafac PG Miglyol 829 Softisan 645 Miglyol 812 Miglyol 8 Capryol 9 Cottonseed oil Imwitor 38 Softigen 71 Imwitor 742 Imwitor 988 Imwitor 491 Hexylene glycol Akomed R Myvacet 9-45K S.E.L.F. 27A* S.E.L.F. 27B* S.E.L.F. 27C** S.E.L.F. 27D** S.E.L.F. 27E** S.E.L.F. 27F** S.E.L.F. 27G* S.E.L.F. 27H** * Semisolid at room temperature ** Liquid at room temperature Table 2 Excipient mixtures used to evaluate solubility at elevated temperature Serial number Excipients Proportion 1 Citric acid (1.%) + HPBCD* (% solution in water) 1. ml ml 2 Propylene glycol + HPBCD 2.25 g g 3 Propylene glycol + citric acid + HPBCD 3. g +.45 g g 4 Glycerin + HPBCD 3.5 g + 1. g 5 Glycerin + citric acid + HPBCD g +.45 g + 1. g 6 Transcutol HP + HPBCD 3.5 g + 1. g 7 Transcutol HP + citric acid + HPBCD g +.4 5g + 1. g 8 Cremophor ELP + Transcutol HP 1. g g 9 Cremophor ELP + propylene glycol 1. g g 1 Transcutol HP + propylene glycol 2.25 g g 1 Propylene glycol + polyethylene glycol + Transcutol HP 2.g +.45 g + 2. g 12 Propylene glycol + glycerin + Transcutol HP 2. g +.75 g g 13 Transcutol HP + hexylene glycol 3. g g 14 Gelucire 44/14 + Transcutol HP + propylene glycol 1.5 g g g 15 Cremophor ELP + PEG 2.75 g g 16 Cremophor ELP + propylene glycol + HPBCD 2. g + 1. g+ 1.5 g 17 Capmul MCM + Cremophor ELP 1. g g 18 Capmul MCM + Cremophor RH 1.5 g + 3. g 19 Captisol + Cremophor ELP + PEG 1. g g +.75 g Captisol + Cremophor ELP + propylene glycol 1. g + 2. g g 21 Cremophor ELP + propylene glycol + Imwitor g +.9 g g 22 Cremophor ELP + Transcutol HP + Imwitor 38.9 g +.45 g g 23 Cremophor ELP + propylene glycol + Imwitor g g g 24 Propylene glycol + Transcutol + Imwitor 38.9 g +.9 g g 25 Gelucire 44/14 + propylene glycol + Imwitor g g g 26 Gelucire 44/14 + Cremophor ELP 2.25 g g 27 Myvacet 9-45K + Lauroglycol + Labrasol 2.25 g +.45 g + 1. g * HPBCD = hydroxypropyl-beta-cyclodextrin

4 (BHT) were added as preservatives. Accelerated stability studies were then conducted on all formulations to determine the shelf-life of each drug product. The manufacturing process involved melting the excipients at a temperature of ~65 C and then dispersing the API into each mixture by stirring. The molten mixtures were then placed into hard gelatin capsules (Licaps from Capsugel). Lots 5 and 6 were manufactured by dissolving the API into excipient preparations 27F and 27H, respectively. Results and discussion Stage 1: Vehicle screening studies. None of the individual excipients subjected to the screening studies achieved the target solubility (~ mg/ml) at both ambient and elevated temperatures. Table 4 lists which excipients displayed 1) insolubility and partial wetting properties and which were 2) partially soluble at elevated temperatures. The excipients that were screened but not listed in the table were observed to have neither wetting nor solubilization properties. Stage 2: Mixture approach to solubility studies at elevated temperatures. The API was partially soluble in mixtures 1 to 11, 14, 17, 18,, 21, 22, 24, and 25, as numbered in Table 2. None of the mixtures, however, could obtain the target solubility of ~ mg/ml. Table 3 Stage 3: Selection of optimal mixture. The in vitro dissolution rates in.1 N HCl of all six excipient mixtures used to formulate the LFHC prototypes are shown in Table 5 and Figure 1. Note that the initial dissolution of Lot 2 and Lot 4 was slower (13 percent after 1 minutes) than those of the other prototypes (>65 percent). The different results can be attributed to the different properties of the excipients and the different ratios of excipients that were used. Overall, the dissolution profiles provide a reasonable spread of prototype formulations for conducting in vivo animal studies. Although a clear solution was not obtained, Lot 1 and Lot 3 dissolved 75 percent of the API in 45 minutes, which justifies further evaluation of both prototype formulations in animal studies. No significant changes in the appearance of the capsule shell and the contents of the capsule were noted during accelerated stability studies. Chemical stability was also encouraging. Finally, no leakage of the contents was observed, even though the capsules were not sealed. Figures 2 and 3 show the accelerated stability data for lots 1 and 3. Excipient preparations 27F and 27H (lots 5 and 6) were not considered for further assessment. They will only be re-evaluated if required, based on the results of the in vivo studies conducted using lots 1 and 3. Mixtures used to evaluate in vitro dissolution (milligrams per capsule) Gelucire 44/14 Imwitor 38 Vitamin E TPGS HPBCD Propylene glycol BHA BHT Lot Lot Lot Lot Table 4 Observations during solubility studies at elevated temperature Insoluble with partial wetting properties Partially soluble Gelucire 44/14, Gelucire 5/13, Polysorbate, Propylene glycol, Miglyol 81, Imwitor 38, Imwitor 988, S.E.L.F. 27F, and S.E.L.F. 27H Crillet 1 HP, Solutol HS 15, glycerin, Capryol 9, Imwitor 491, Imwitor 742, Labrasol, Cremophor RH, MCT, Capmul MCM, and hexylene glycol. Table 5 In vitro dissolution of selected mixtures in.1 N HCl (mean percentage dissolved) 1 min min 3 min 45 min min Infinity Lot Lot Lot Lot S.E.L.F. 27F (Lot 5) S.E.L.F. 27H (Lot 6)

5 Figure 1 In vitro dissolution of selected API-excipient mixtures in.1 N HCl Lot 1 Lot Lot 2 S.E.L.F. 27F Figure 2 Lot 1 in vitro dissolution data Lot 3 S.E.L.F. 27H T = T = 1 month Figure 3 Lot 3 in vitro dissolution data Conclusion Gelatin LFHCs offer a simple yet effective means of formulating compounds with low aqueous solubility. Even though complete solubilization was not achieved, the in vitro dissolution profile of a low-solubility compound was improved by associating the API with an optimal mixture of solubilizers and bioavailability-enhancers. An excipient-mixture approach that takes into consideration the different properties of excipients was used to arrive at this optimal ratio. T&C References 1. Lipinski, CA. Reducing the investment made in likely drug development failures. In Transforming the Pharmaceutical Industry: Adapting to Change in Technology and Markets. Cambridge Healthtech Institute, Newton, MA, Tong, WQ. Developability Assessment Supporting Drug Candidate Selection [Powerpoint]. UT: UoU Integrated Drug Development Process Course; Wiser L, Gao X, Jasti B, Li X. Solubility of pharmaceutical solids. In: Hu M, Li X, eds. Oral Bioavailability: Basic Principles, Advanced Concepts, and Applications. Hoboken, NJ: John Wiley & Sons, Inc.; Cowan-Lincoln M. Improve the bioavailability of poorly soluble drugs. PFQ. February/March 12: Kommuru TR, Gurley B, Khan MA, Reddy, IK. Selfemulsifying drug delivery systems (SEDDS) of coenzyme Q1: formulation development and bioavailability assessment. Int J Pharm. 1;212(2): Lipinski CA, Lombardo F, Dominy BW, Feeney PJ. Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv. Drug Deliv. Rev. 1;46(1-3): Keseru GM, Makara GM. Hit discovery and hit-tolead approaches. Drug Discov Today. 6;11(15-16): Anderson NG. Practical Process Research and Development: A Guide for Organic Chemists. 2nd ed. Oxford, UK: Elsevier, Inc.; 12: Howard JR, Gould PL. Drug release from thermosetting fatty vehicles filled into hard gelatin capsules. Drug Dev. Ind. Pharm. 1987;13(6): T = T = 1 month Amol Kheur is a technical project leader; Anil Kane is executive director, global head of formulation sciences; Mohammad Aleem is a senior research chemist; and Maureen McLaughlin is a senior manager, analytical development at Patheon Pharmaceutical Development Services, 4721 Emperor Blvd., Suite, Durham, NC Tel Website: Kiran Kumar Tumbalam and Shivaprakash Poojary are former employees.