Compatibility of verapamil hydrochloride with penicillin admixtures during simulated Y-site injection

The compatibility of verapamil hydrochloride during simulated Y-site injection with i.v. admixtures containing 11 different penicillins was studied. Admixtures of penicillin G potassium (62.5 mg/mL), nafcillin sodium (40 mg/mL), oxacillin sodium (40 mg/mL), ampicillin sodium (40 mg/mL), carbenicillin disodium (40 mg/mL), methicillin sodium (40 mg/mL), ticarcillin sodium (40 mg/mL), azlocillin sodium (40 mg/mL), mezlocillin sodium (40 mg/mL), piperacillin sodium (40 mg/mL), and amdinocillin (20 mg/mL) were prepared in both 5% dextrose injection and 0.9% sodium chloride injection in minibags. Verapamil hydrochloride injection 4 mL (10 mg) was then added to each admixture, and the admixtures were examined macroscopically and microscopically for precipitate immediately and at 15 minutes and 24 hours after mixing. To simulate Y-site injection of verapamil, verapamil hydrochloride injection 1 mL (2.5 mg) was added to 1 mL of each penicillin admixture in a test tube. For admixtures in which precipitates formed, the pH was recorded before and after verapamil was added to the admixtures. Loss of verapamil hydrochloride when mixed with the penicillin admixtures was determined using reverse-phase high-performance liquid chromatography. Addition of verapamil hydrochloride to admixtures containing nafcillin sodium, oxacillin sodium, ampicillin sodium, and mezlocillin sodium resulted in substantial loss of verapamil hydrochloride. The results for the Y-site injection study showed visible precipitation with the same penicillin admixtures. Because a precipitate formed when verapamil hydrochloride was added to nafcillin sodium, oxacillin sodium, ampicillin sodium, or mezlocillin sodium in the diluents studied, we recommended that verapamil hydrochloride be administered separately or that the i.v. tubing be flushed thoroughly before and after this drug is administered through a Y-injection site with these penicillin admixtures.