Nisoldipine (Sular -Zeneca), a dihydropyridine calcium-channel blocker structurally similar to nifedipine, has been approved for marketing by the US Food and Drug Administration. It is available in an oral extended-release formulation for treatment of hypertension.

Reports of increased mortality associated with calcium-channel blockers have caused concerns among patients taking these drugs and their physicians.

Mibefradil dihydrochloride (Posicor - Roche), a chemically distinct nondihydropyridine calcium-channel blocker, has been approved by the US Food and Drug Administration (FDA) and is being heavily promoted as the first T-type calcium-channel blocker for treatment of hypertension and chronic stable angina.

Serious adverse interactions between drugs continue to be reported. Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

Changes caused by one drug in the absorption, distribution, metabolism or excretion of another may lead to a pharmacokinetic adverse drug interaction (DN Juurlink et al, JAMA 2003; 289:1652). Additive drug interactions, such as vasodilation caused by both sildenafil (Viagra) and nitrates, can also have adverse effects.

The ability of grapefruit juice to increase serum concentrations of drugs was first discovered during a study of the effect of ethanol on felodipine (Plendil) pharmacokinetics. Double-strength grapefruit juice used to disguise the taste of ethanol resulted in higher than expected serum concentrations of felodipine (DG Bailey et al, Clin Invest Med 1989; 12:357).

The importance of adequate control of hypertension in preventing organ damage and death is well established, but the choice of drugs is still controversial. Three recent drug trials, one supporting initial therapy with a diuretic, the second favoring an angiotensin converting enzyme (ACE) inhibitor, and the third showing equivalence between a calcium-channel blocker and an angiotensin-receptor blocker (ARB) have intensified the debate.

American College of Cardiology/American Heart Association (ACC/AHA) guidelines for treatment of hypertension were last published in 2018. Treatment of hypertensive urgencies and emergencies is not discussed here.