Objectives The objective of this study was to evaluate the compatibility of 10 commonly used active pharmaceutical ingredients (APIs) compounded in oral suspensions using a globally available suspending vehicle (SyrSpend SF PH4 liquid): caffeine 10.0 mg/mL, carvedilol 1.0 mg/mL, clomipramine hydrochloride 5.0 mg/mL, folic acid 1.0 mg/mL, hydrochlorothiazide 5.0 mg/mL, loperamide hydrochloride 1.0 mg/mL, methotrexate 2.5 mg/mL, nadolol 10.0 mg/mL, naltrexone hydrochloride 1.0 mg/mL and pentoxifylline 20.0 mg/mL, stored at both controlled refrigerated (2–8°C) and room (20–25°C) temperature.

Methods Compatibility was assessed by measuring the per cent recovery at different time points throughout a 90-day period. Quantification of the APIs was performed by high performance liquid chromatography (HPLC-UV) using a stability-indicating method.

Results Methods were adequately validated. Forced degradation studies showed that at least one parameter influenced the stability of the APIs. All suspensions were assayed and showed API contents of between 90% and 110% over 90 days.

Discussion Given the percentage of recovery of the APIs within the suspensions, the expiration date of the final products (API+vehicle) was found to be at least 90 days for all suspensions, for both controlled refrigerated and room temperature.

Conclusions The results suggest that SyrSpend SF PH4 liquid is a stable suspending vehicle for compounding APIs from different pharmacological classes.