How much antibiotic suspension is enough?

Objectives. Pilot data suggest that inadequate antibiotic volumes are often dispensed. Study goals were to determine the frequency of inadequate antibiotic volumes dispensed by local pharmacies, develop prescription-writing guidelines to ensure that adequate antibiotic suspension volumes are dispensed, and document the adequacy of verbal/written counseling pharmacists provide. Methods. Sixty-one local pharmacies filled prescriptions for penicillin potassium (PCN; 250 mg/5 mL [5 mL orally 3 times daily for 10 days]) and Bactrim (trimethoprim-sulfamethoxazole [TMP-SMX] 5 mL orally twice daily for 10 days). The prescriptions noted only to "dispense a 10-day supply." Volumes were measured first as total amount dispensed and then into total doses dispensed. Written/verbal instructions were documented. Results. The volume of PCN dispensed was 195 +/- 25 mL (range: 105-222 mL) for an average of 29.4 doses, where 30 doses were needed. TMP-SMX dispensed had a volume of 107 +/- 5 mL (range: 98-120 mL) resulting in an average of 16.5 doses, where 20 doses were needed. Twenty pharmacies (33%) did not dispense a measuring device. Verbal counseling by the pharmacist and written instructions were not uniformly given. Conclusions. We suggest calculating the actual volume needed plus an additional 10% to 30% of volume (depending on the viscosity). The prescription should also request a medication-measuring/administering device. Patient counseling and instruction should be expanded.