Evaluation of physicochemical characteristic of rifampicin extemporaneous suspension in specific time and conditions

Abstract

Rifampicin is one of the first line medicines for treatment of tuberculosis (TB). Some patients such as children cannot take the solid dosage form orally and need oral liquid preparations. In those cases, pharmacists prepare rifampicin extemporaneous suspensions. However, the stability of rifampicin extemporaneous suspensions in a tropical country such as Thailand has not been investigated. A lack of stability information means that the compounding pharmacist is responsible for ensuring the stability efficacy and safety of the suspension. Rifampicin extemporaneous suspension was prepared at 25 mg/mL and kept under 3 temperature conditions: refrigerated (7±3°C), room temperature and accelerated temperature (45±5°C). The color, pH and viscosity of the extemporaneous solution was recorded after 0, 7, 14, 30, 45 and 60 days and the rifampicin content were determined by HPLC analysis. There was no change in the color of suspensions stored at room temperature and refrigerated temperature, but the color did change under 45±5°C. The pH remained stable under all three conditions of storage. The suspensions decreased in viscosity as viscometer spindle speed was increased, and this was unaffected by the different storage conditions. All samples stored under refrigerated temperature and room temperature retained more than 90% of their initial rifampicin concentration for 60 days. However, under the accelerated temperature, only 19.51% of the initial concentration of rifampicin remained on day 60 (p<0.05). Thus, testing for stability at a range of temperatures is important when extemporaneously preparing pharmaceutical suspensions in tropical climates.