Calcium antagonists in cardiology: update on sustained-release drug delivery systems.

One limitation of standard oral formulations of calcium antagonists has been the need for multiple daily dosing. Sustained-release dosage forms permit simpler regimens and a smoother therapeutic effect. Differences in drug pharmacokinetic and pharmacodynamic properties have led to development of several sustained-release delivery systems. Three major types are available: the osmotic pump, coated pellet, and slow-dissolving material released from a matrix. Each is currently utilized with specific calcium antagonists. The osmotic pump system with nifedipine (Procardia XL, Pfizer) allows once-daily dosing as well as improvements in certain side effects. Verapamil is available in formulations employing dissimilar release systems. The original sustained-action products (Calan SR, Searle; Isoptin SR, Knoll) utilize a matrix system; a subsequent product (Verelan; Lederle, Wyeth-Ayerst, A. H. Robins) utilizes timed-release pellets. Importantly, clinical efficacy appears to be maintained with these several drugs and formulations for their approved indications. Although a specific formulation may alter the absorption, metabolism, excretion, and blood levels of a drug, it does not alter basic drug properties. Thus, the major impact of sustained-release drug delivery system lies in potential compliance improvement and possible reduction of side effects related to serum drug profiles.