Stability of pergolide mesylate oral liquid at room temerature

Pergolide mesylate (proprietary name Permax) is used to treat equine Cushing's syndrome. Since pergolide mesylate has been removed from the market, the tablets are no longer available. Therefore, pergolide mesylate preparations have to be compounded for veterinary use. Compounded oral liquid formulations have been given arbitrary beyond-use dates of 14 days (aqueous) to 90 days (oil based). The goal of this study was to determine the stability of a 0.2 mg/mL pergolide oral liquid prepared according to a previousy published formulation and stored at room temperature. The sample preparation and the high-performance liquid chromatographic assay described in the United States Pharmacopeia-National Formulary were modified to treat the oral liquid as a suspension. The assay was evaluated prior to its use. A linear relationship was found between peak area and concentration with Rsquared values ranging for 0.989 to 0.999 for three of the sample calibration plots. The daily reproducibility and day-to-day variability of single injections of the assay were found to have relative standard deviations of 1.26% and 3.52%, respectively. Analysis of the oral liquid and a blank oral liquid (without pergolide mesylate) exposed to acid and heat demonstrated that the excipients and degradation species did not interfere with the drug peak. Samples, in replicates of five, were stored at room temperature, then pulled at specific intervals (1, 2, 4, 8, 12, and 16 weeks) and stored at -80 deg C for assay at a later date. After 16 weeks at room temperature, the drug degraded to 71% of its original concentration. The time to reach 90% potency (t90) of pergolide mesylate was calculated to be 6.5 weeks (45 days). Degradation studies at 35 deg C, 45 deg C, and 60 deg C are in progress.