Stability of bethanechol chloride, pyrazinamide, quinidine sulfate, rifampin, and tetracycline hydrochloride in extemporaneously compounded oral liquids

The stability of five drugs commonly prescribed for use in oral liquids but not commercially available as such was studied. Bethanechol chloride 5 mg/mL, pyrazinamide 10 mg/mL, quinidine sulfate 10 mg/mL, rifampin 25 mg/mL, and tetracycline hydrochloride 25 mg/mL were each prepared in a 1:1 mixture of Ora-Sweet and Ora-Plus (Paddock Laboratories), a 1:1 mixture of Ora-Sweet SF and Ora-Plus, and cherry syrup and placed in 120-mL amber clear polyethylene terephthalate bottles. Three bottles of each liquid were stored at 5 degrees C and three at 25 degrees C, all in the dark. Samples were taken initially and at various times up to 60 days for analysis by high-performance Liquid chromatography and assessment of appearance and odor; pH was measured. A mean of at least 90% of the initial drug concentration was retained for 60 days in the liquids containing bethanechol chloride, pyrazinamide, or quinidine sulfate and for 28 days in the rifampin-containing liquids and the mixture of tetracycline hydrochloride and Ora-Sweet-Ora-Plus at both 5 and 25 degrees C. Tetracycline hydrochloride concentrations of 90% or more of the initial concentration were retained in the liquids prepared with Ora-Sweet SF-Ora-Plus for 10 days at 5 degrees C and 7 days at 25 degrees C and in those prepared with cherry syrup for 7 days at 5 degrees C and 2 days at 25 degrees C. No substantial changes in the appearance, odor, or pH of any liquid were observed. At 5 and 25 degrees C, bethanechol chloride 5 mg/mL, pyrazinamide 10 mg/mL, and quinidine sulfate 10 mg/mL were stable in three extemporaneously compounded oral liquids for 60 days and rifampin 25 mg/mL was stable for 28 days. The stability of tetracycline hydrochloride 25 mg/mL varied with the vehicle.