Stability study of nilvadipine in bulk drug and pharmaceutical capsules by high performance liquid chromatography

A simple, stability-indicating, liquid chromatographic method has been developed for the assay of nilvadipine in the presence of its alkaline-induced degradation products. A mu Bondapak-C-18 column was used with a mobile phase consisting of acetonitrile/0.01 M sodium acetate (55:45, v/v) adjusted to pH 3.5 with acetic acid at a flow rate of 1.8 mL min(-1). With procaine hydrochloride as an internal standard, quantitation was achieved with UV detection at 254 mn based on the peak areas ratios. Determination of nilvadipine was possible over the concentration range 0.096-0.64 mu gmL(-1) with limit of detection of 0.032 mug/mL (8.3 x 10(-8) M). Between-day and within-day relative standard deviations were lower than 2%. The proposed method was successfully applied to the determination of nilvadipine in bulk and capsule form, with a high percentage of recovery. Moreover, the method was utilized to investigate the kinetics of the degradation process at different temperatures. The apparent first-order rate constant, half-life and activation energy were calculated. The proposed method was extended to the in vitro detection of nilvadipine in human urine samples.