Stability of rifabutin in two extemporaneously compounded oral liquids

The stability of rifabutin 20 mg/mL in two oral liquids was studied. Powder from 100 150-mg rifabutin capsules was placed in a glass mortar. Cherry syrup (pH 2.9) or a 1:1 mixture of Ora-Sweet and Ora-Plus (Paddock Laboratories) was added to produce 750 mL of each formulation, which was then stored in 2-oz plastic prescription bottles. Three bottles of each formulation were stored at 4, 25, 30, and 40 degrees C. At 0, 1, 2, 4, 8, and 12 weeks, the bottles were collected and allowed to remain at room temperature for one hour; samples of about 1 mL were collected from each bottle, weighed, and assayed for rifabutin content by high-performance liquid chromatography. The rifabutin liquids prepared with cherry syrup and stored at 4, 25, and 30 degrees C lost a mean of < 8% of the initial drug concentration during the 12-week study; at 40 degrees C, the liquids lost > 10% of the initial drug concentration by 12 weeks. There was a mean loss of < 5% of the initial rifabutin concentration in all the liquids prepared with Ora-Sweet and Ora-Plus. The liquid prepared with cherry syrup, upon standing, showed a tendency for some of the ingredients to float. The suspension prepared with Ora-Sweet and Ora-Plus had a tendency to retain bubbles after it was shaken, but the ingredients did not settle upon standing. Rifabutin 20 mg/mL in two extemporaneously compounded oral liquids prepared from capsules and sweetened vehicles was stable for at least 12 weeks at 4, 25, 30, and 40 degrees C with the exception of rifabutin in cherry syrup, which was stable for only 8 weeks at 40 degrees C.