Stability and Beyond-Use Date of a Compounded Thioguanine Suspension.

Background: Thioguanine (TG) is available only in the form of 40 mg tablets in the United States, and the patient population in which TG is used comprises mostly children. Recognizing its importance as a therapeutic agent and limited stability data for its compounded preparation, the United States Pharmacopoeia has listed TG in its priority list of compounded preparations monographs. Objective: The goal of the present study was to generate stability data and establish a beyond-use date for compounded TG suspension. Methods: Suspensions were compounded using TG tablets and ORA-Plus and ORA-Sweet as vehicles. A robust high-performance liquid chromatography method was developed and validated. TG and guanine (G) in suspensions were quantified immediately after compounding and at regular intervals for 90 days. Physical stability of suspensions was evaluated by observation of organoleptic properties. Results: Results from the study indicate that average TG levels in suspensions remained above 90% of the starting concentration and G formation was less than 2.5% for 90 days. There was no statistically significant difference in the amount of TG degraded over 90 days between suspensions stored at room temperature and in refrigerated conditions. There was also no statistically significant difference in G concentration of suspensions between day 0 and day 90. Conclusion: TG suspensions are stable for 90 days when stored at room temperature or refrigerated conditions and the beyond-use date can be set to 90 days.

Design and Performance of an Inexpensive Water Activity Meter.

Water activity refers to the amount of water in a system that is available for microbial growth. Commercial water activity meters are precision instruments with the ability to determine water activity to within 0.001 units and carry prices of $10,000 or more. The purpose of the study was to build a robust water activity meter from commercially available components and measure the water activity of liquids commonly used in compounded formulations. SHT-85 sensors were connected to an Adafruit Feather HUZZAH microcontroller. Standard salt slurries and common oral liquid vehicles were monitored in airtight containers until equilibrium was reached. Standard curves were used to convert sensor outputs to water activity values. The standard curves were linear with R2 >0.99. Oral liquid vehicles showed water activity values between 0.62 and 0.99. Samples equilibrated within 9.5 hours in 16-ounce jars or 2.5 hours in 20-mL vials. Stirring the sample during measurement reduced equilibration time in 16-ounce jars, but not in 20-mL vials. The inexpensive meter was accurate and precise in measuring the water activity of standards and selected oral vehicles. An accurate and precise water activity meter was constructed at a cost of approximately $150. Common oral formulation components have a water activity of >0.6, the United States Pharmacopeial threshold for requiring a preservative. Pharmacists should use caution when diluting preserved vehicles.