Stability of rifampin in two suspensions at room temperature

The objective of our study was to determine the stability of rifampin (rifampcin) in two extemporaneously prepared suspensions at room temperature. Two suspensions were prepared in syrup by using intravenous rifampin (A) or rifampin capsules (B). Each suspension was stored in five plastic prescription bottles. During the first week, the mean measured concentrations of rifampin were nearly 100% of initial concentration in suspension A, but were 77-83% of the expected (labelled) concentration in suspension B. The maximum concentrations of rifampin were observed immediately after preparation of suspension A, but not until 14 days in suspension B. On day 56, the mean concentration of rifampin was about 95% of initial concentration in suspension A, and close to 90% of the labelled potency (10 mg/ml) in suspension B. Rifampin was found to be chemically stable in each suspension for 56 days at room temperature. Suspensions prepared from the capsules may be non-homogeneous and lead to unsatisfactory dosing.