Physicochemical and Microbiological Stability of Pyrimethamine in Paraben-free PCCA Base, SuspendIt

Abstract

Pyrimethamine is an antiparasitic compound available only in tablet form for oral administration. A review of the therapeutic uses of pyrimethamine 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 pyrimethamine currently exists. Pyrimethamine is available commercially only as 25-mg tablets. 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 pyrimethamine suspension in 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. A robust stability-indicating high-performance liquid chromatographic assay for the determination of the chemical stability of pyrimethamine in PCCA SuspendIt was developed and validated. Suspensions of pyrimethamine were prepared in PCCA SuspendIt at a 2-mg/mL concentration, selected to provide flexibility in customizing individual doses. 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, and 42. 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 pyrimethamine concentrations did not go below 96% of the label claim (initial drug concentration) at both temperatures studied. No microbial growth was observed. pH values remained constant. The viscosity of the suspensions allowed easy re-dispersal of the drug particles upon shaking. This study demonstrates that pyrimethamine is physically, chemically, and microbiologically stable in PCCA SuspendIt for 42 days stored in the refrigerator and at room temperature, thus providing a viable, compounded alternative for pyrimethamine in a liquid dosage form.