Physicochemical Stability of Compounded Allopurinol Suspensions in PCCA Base, SuspendIt.

Allopurinol is an orally administered inhibitor of xanthine oxidase used primarily in the treatment of hyperuricemia associated with gout. Allopurinol reduces serum and urinary uric acid concentrations. Its use should be individualized for each patient. The dosage of allopurinol to accomplish full control of gout and to lower serum uric acid to normal or near-normal levels varies with the severity of the disease, and needs to be flexible to permit precise, customized dose titration for individual patients. This flexibility is readily achieved using an oral liquid dosage form. However, no commercial liquid dosage form of allopurinol currently exists. Allopurinol is commercially available as 100-mg and 300-mg scored tablets. An extemporaneously compounded suspension from pure drug powder or commercial tablets would provide a convenient option to meet unique patient needs. The purpose of this study was to determine the physicochemical stability of extemporaneously compounded allopurinol 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 allopurinol concentrations to provide stability documentation over a bracketed concentration range for eventual use by compounding pharmacists. A robust stability-indicating ultra-performance liquid chromatography assay for the determination of the chemical stability of allopurinol in SuspendIt was developed and validated. Suspensions of allopurinol were prepared in SuspendIt at 10.0-mg/mL and 20.0-mg/mL concentrations, selected to represent a range within which the drug is commonly dosed. Samples were stored in plastic amber prescription bottles at two temperature conditions (5°C and 25°C). Samples were assayed initially and at the following time points: 7 days, 14 days, 30 days, 45 days, 60 days, 88 days, 120 days, and 182 days. Physical data such as pH, viscosity, and appearance were also noted. 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. The study showed that allopurinol concentrations did not go below 93% of the label claim (initial drug concentration) at both temperatures studied. Viscosity and pH values also did not change significantly. This study demonstrates that allopurinol is physically and chemically stable in SuspendIt for 180 days in the refrigerator and at room temperature, thus providing a viable, compounded alternative for allopurinol in a liquid dosage form, with an extended beyond-use-date to meet patient needs.