Summary
The pharmacokinetics of verapamil in five healthy volunteers were investigated on 4 occasions during chronic administration of deuterated verapamil. There was no statistically significant difference in oral clearance, terminal half-life, bioavailability, morning trough level and peak concentration or in the time of their occurrence on the four occasions. The plasma clearance, however, exhibited considerable inter- and intra-individual variation, ranging between 26.3% and 85.4% and 12.0% and 48.0%, respectively. Comparison of these pharmacokinetic parameters with data from previous single dose studies in the same subjects revealed a significant (p<0.05) decrease in the clearance and an increase in the apparent bioavailability of verapamil during chronic administration, although no difference in the half-life was found. Due to the considerable variation in the oral clearance of verapamil during chronic dosing, steady-state conditions in a strict pharmacokinetic sense may never be attained, and pharmacokinetic data obtained in single dose studies will be of limited value in predicting steady-state plasma concentrations.
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Eichelbaum, M., Somogyi, A. Inter- and intra-subject variation in the first-pass elimination of highly cleared drugs during chronic dosing. Eur J Clin Pharmacol 26, 47–53 (1984). https://doi.org/10.1007/BF00546708
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DOI: https://doi.org/10.1007/BF00546708