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.