Once daily nifedipine: the formulation dictates the pharmacokinetic characteristics and the therapeutic responses

Nifedipine as a pharmacologic agent for treating hypertension and angina pectoris has been available worldwide since the early 1980's. However, the formulation of nifedipine has undergone a number of modifications over time to improve the pharmacokinetic profile and administration regimen from 3 times daily to once daily. Nifedipine Gastrointestinal Therapeutic System (GITS) is the most widely studied of the once daily formulations from both a pharmacokinetic and clinical perspective. Nifedipine GITS was registered in most major countries worldwide based on both clinical pharmacology and clinical trial data in adequately powered studies. Moreover, outcome trials in both hypertension (INSIGHT) and angina pectoris (ACTION) have been completed and published. Other once daily modified release nifedipine formulations are available in a number of countries but limited published data is available on these formulations. A Pubmed (Medline) search using the terms "nifedipine pharmacokinetics" yielded 162 articles of which 7 provided detailed pharmacokinetic values in head to head comparisons of nifedipine GITS and another once a day formulation. These published pharmacokinetic studies have failed to show that any of the other formulations is consistently bioequivalent to the reference formulation, nifedipine GITS. In addition, other Pubmed searches yielded limited data from comparative clinical studies, which show significant differences in favor of the nifedipine GITS formulation in terms of blood pressure control and activation of the sympathetic nervous system. With limited data comparing once daily formulations of nifedipine to nifedipine GITS and no data comparing between other once a day formulations, for both pharmacokinetic and therapeutic reasons, the evidence indicates that patients should not be switched between once daily formulations of nifedipine.