(M1230-04-20) Development of an In Vitro Release Method for Mechlorethamine Hydrochloride Topical Gel

Purpose: In vitro release testing (IVRT) is an established compendial method described in the United States Pharmacopeia (USP) General Chapter < 1724 >, and it is often recommended as a component of characterization-based approaches for evaluating bioequivalence of semi solid dosage forms such as gels. Development of an IVRT method for drug products such as Valchlor^® (mechlorethamine hydrochloride) gel, eq 0.016% base is challenging, because the drug substance, mechlorethamine hydrochloride, is a highly reactive compound and unstable in various media such as water. The purpose of the current study is to develop a sensitive and discriminatory IVRT method for mechlorethamine hydrochloride topical gel.

Methods: Screening studies were performed to identify suitable receptor solutions that may be used in an IVRT study by assessing the solubility of mechlorethamine hydrochloride in propylene glycol, diethylene glycol monoethyl ether (Transcutol®), isopropyl alcohol, glycerin and mixtures containing varying amounts of each solvent. Based on the data from the solubility studies, stability of mechlorethamine was then studied at 32^oC in the selected receptor solutions. Specifically, solutions of mechlorethamine were prepared in two solvent systems: solvent system A (propylene glycol: water 50:50 v/v with 0.5% w/v ascorbic acid) and solvent system B (diethylene glycol monoethyl ether: water 50:50 v/v with 0.5% w/v ascorbic acid). At each sampling time (0 hr and 4 hrs) samples were withdrawn from each vial and analyzed. The two receptor solutions and two different types of membrane, nylon (SteriTech^®) and a polytetrafluoroethylene (PTFE, Millipore Flouropore^®), were evaluated in the method development studies. Pilot IVRT studies were conducted using a vertical diffusion cell apparatus with a permeation area of 0.636 cm² and receptor volume of 14 mL. 300 mg/cm² of mechlorethamine hydrochloride topical gel was dosed onto the membrane after it was equilibrated at 32 ± 1 ^oC (measured at the surface of the membrane) with the receptor solution. At specific time points (0.5, 1, 2 ,3 and 4 hours), 500 µL samples were withdrawn from the receptor solution. Mechlorethamine content in all the samples were quantified using a liquid chromatography–mass spectrometry method (LC-MS). n=3 cells per membrane were evaluated for each solvent system in this method development work.

Results: Mechlorethamine was soluble in the solvent mixtures compared to the individual solvents. The stability data indicated that mechlorethamine was more stable in solvent system A after 4 hours of incubation at 32 ^oC (Figure 1). Pilot IVRT data (Figure 2) suggested that the release of mechlorethamine was linear (r²>0.97) over the 4-hour IVRT study duration when nylon membrane was utilized with solvent system A. The observed release profile did not meet the currently recommended threshold for linearity for solvent system A with the PTFE membrane, or solvent system B with either membrane.

Conclusion: The current work demonstrates that it may be feasible to develop an IVRT method for mechlorethamine hydrochloride topical gel using a vertical diffusion cell. Mechlorethamine hydrochloride is stable and soluble in solvent system A, and compatible with the nylon membrane evaluated in this study. Additional work is needed to assess the discriminatory capability of the method to be able to use such a method as a component of characterization-based approaches for evaluating bioequivalence.

Acknowledgments: This project was supported in part by an appointment (Ann-Marie Ako-Adounvo) to the Research Participation Program at the Office of Research and Standards, Office of Generic Drugs, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and FDA. The views expressed in this abstract do not reflect the official policies of the U.S. Food and Drug Administration or the U.S. Department of Health and Human Services; nor does any mention of trade names, commercial practices, or organization imply endorsement by the United States Government

Figure 2: IVRT release profile of mechlorethamine in solvent system A and solvent system B using the nylon membrane



Figure 1: Mechlorethamine stability in solvent system A and B (Data are presented as Mean ± SD, n = 3)