Evaluation of five procedures for measuring nonstandard doses of nifedipine liquid

Five methods for removing the maximum volume of liquid from a nifedipine capsule were evaluated for efficiency and reproducibility, and the concentration of nifedipine in Procardia and Adalat 10- and 20-mg capsules was determined The methods evaluated were the needle puncture and squeeze method; the scissors method; the needle and syringe, one-hole method; the needle and syringe, two-hole method; and the capsule in syringe barrel method. The liquid content of 10 Adalat 10-mg capsules was removed by each method, the volume was determined by the weight and specific gravity of the nifedipine liquid, and the mean volumes of nifedipine liquid were compared. A stepwise procedure for using the needle and syringe, one-hole method was developed. The mean nifedipine concentration in Procardia 10- and 20-mg capsules was determined by ultraviolet spectrophotometry by using 30 capsules of each brand and strength. The needle and syringe methods were the most reproducible and efficient procedures for obtaining a desired milligram dosage of nifedipine from the capsules. The two-hole method would be less practical in the clinical setting, however, because it is time consuming and cumbersome. The mean assayed nifedipine concentration in the Procardia and Adalat 10- and 20-mg capsules was within 10% of the concentration reported by the manufacturer for each specific product lot number. Based on reproducibility and efficiency, the needle and syringe methods are the best methods for quantitation of liquid nifedipine doses for patient administration.