Physiochemical and Microbiological Stability of Azathioprine Suspensions in PCCA Base, SuspendIt

Abstract

Azathioprine is used to treat the symptoms of rheumatoid arthritis and for the prevention of transplant rejection. A review of the therapeutic uses of Azathioprine reveals the need for flexibility in dosing. This flexibility is readily achieved using an oral liquid dosage form. However, no commercial liquid dosage form of Azathioprine currently exists. Azathioprine is commercially available only as a 50-mg tablet. An extemporaneously compounded suspension from pure drug powder would provide a flexible, customizable option to meet unique patient needs with convenient and accurate dosing options. The purpose of this study was to determine the physicochemical and microbiological stability of extemporaneously compounded Azathioprine suspensions in the PCCA Base, SuspendIt. This base is a sugar-free, paraben free, dye-free, and gluten-free thixotropic vehicle containing a natural sweetener obtained from the monk fruit. The study design included two Azathioprine concentrations to provide stability documentation over a bracketed concentration range for eventual use by compounding pharmacists. A robust stability-indicating high-performance liquid chromatographic assay for the determination of the chemical stability of Azathioprine in PCCA SuspendIt was developed and validated. Suspensions of Azathioprine were prepared in PCCA SuspendIt at 10-mg/mL and 50-mg/mL concentrations, selected to represent a range within which the drug is commonly dosed. Samples were stored in amber plastic prescription bottles at two temperature conditions (5°C and 25°C). Samples were assayed initially, and on the following time points (days): 7, 14, 28, 49, 63, 90, 119, and 182. Physical data such as pH, viscosity, and appearance were also noted. Microbiological stability was tested. All measurements were obtained in triplicate. A stable extemporaneous product is defined as one that retains at least 90% of the initial drug concentration throughout the sampling period and is protected against microbial growth. The study showed that Azathioprine concentrations did not go below 96.8% of the label claim (initial drug concentration) at both temperatures studied. No microbial growth was observed. The pH values remained constant. The viscosity of the suspensions allowed easy re-dispersal of the drug particles upon shaking. This study demonstrates that Azathioprine is physically, chemically, and microbiologically stable in PCCA SuspendIt for 182 days in the refrigerator and at room temperature, thus providing a viable, compounded alternative for Azathioprine in a liquid dosage form, with an extended beyond-use date to meet patient needs.