Improvement of the quantitative determination of verapamil in human plasma

An improvement in the extraction procedure for the quantitative determination of verapamil in human plasma is described. The advantages are: 1. the time involved in the extraction procedure is only 1/3 of that in the original method allowing the extraction of 100 samples in a working day. 2. increased mean recovery from 67% to 85% over the range of 3--90 ng verapamil/ml plasma. 3. less expenditure a) use of cheap plastic tubes instead of stoppered glass tubes. b) 1/2 the amount of heptane required as compared to the original procedure. c) use of air instead of N2 for evaporation. The lower limit of detection is 3 ng/ml which is comparable to that for the original extraction procedure. Within-batch precision over the range of 9--90 ng/ml averages 5.8% and at the lower limit of detection 17.3%. Between-batch precision over the range of 9--90 ng/ml averages 8.5% and at the lower limit of detection 19.7%. No significant difference could be found in the quantitative determination of verapamil in 27 plasma samples from patients undergoing verapamil treatment using the original and modified extraction procedures. This improvement of the extraction procedures simplifies the determination of verapamil and the only additional material required is liquid nitrogen or a suitable solvent cooled with dry ice.