Drug delivery systems for antihypertensive agents.

During the late 1980s and early 1990s, much research effort in the pharmaceutical industry was focused on the development of novel systems for sustained delivery of effective, but intrinsically short-acting, antihypertensive agents. This advance was motivated by a desire both to improve trough/peak ratios (as suggested by the US Food and Drug Administration [FDA]) and also to protect the proprietary patient life for older agents that would otherwise be susceptible to generic substitution. Additional benefits of such sustained-release systems include: improved side-effect profiles, shorter time from development to regulatory approval (because of the already established safety record of the immediate-release compound), improved compliance with medication, and reduced administrative cost. The latter two are presumably related to the fact that patients generally have to use fewer doses of sustained-release than immediate-release preparations. Disadvantages include: generally higher per-dose cost (which includes a licensing fee for the patented delivery system), altered efficacy and potential problems in patients with abnormal absorptive surfaces (gut or skin), and altgered first-pass metabolism rates (compared with immediate-release preparations). Some of the novel drug delivery systems that have already received FDA approval include: alginate matrix, Geomatrix, several formulations of pellet-based systems, several transdermal systems, and the Gastrointestinal therapeutic system (GITS), which releases the pharmacologically active agent at a predictable rate. A novel variant of this last system has been developed, based on the idea that the peak serum concentration of antihypertensive medication will occur just before or at the time of the greatest change in blood pressure (ie, the few hours around awakening). Data are now being gathered to convince authorities that this theoretically advantageous delivery system will be as effective in reducing rates of cardiovascular death, nonfatal stroke, or myocardial infarction as diuretics or beta blockers.