Calcium antagonists in the treatment of hypertension

Nifedipine overdose

Overdose with 300 mg of nifedipine in a 54-year-old woman led to profound hypotension and reflex tachycardia. The patient was treated with intravenous fluids, calcium gluconate, and dopamine. Cardiac rhythm disturbances, hypoglycemia, and myocardial depression were not found. Recovery was rapid and uneventful. The clinical aspects of nifedipine overdose are discussed and possible treatment modalities are given.

Nifedipine as a substitute for converting enzyme inhibitors in the treatment of renovascular hypertension

Nifedipine long acting tablets were substituted for converting enzyme inhibitors in eight patients with renovascular hypertension. A significant drop in blood pressure was observed. Nifedipine was shown to be as effective (in lowering blood pressure) as a drug that acts directly on the renin angiotensin system. These data offer support for previously reported findings that the action of angiotensin II is calcium mediated.

Influence of nicardipine on blood pressure, renal function and plasma aldosterone in normotensive volunteers

The influence of the calcium antagonist nicardipine on intrarenal sodium handling and angiotensin II induced secretion of aldosterone was investigated in 18 normotensive volunteers after the first dose and after 1 week of treatment (20 mg three times daily). A short-lasting natriuresis was observed, which was caused by a decreased reabsorption of sodium localised in both proximal and distal tubules. Log plasma renin activity (PRA) fell significantly on each day during angiotensin II infusion, while log-plasma aldosterone (PA) rose significantly. The log PRA/log PA ratio was increased during nicardipine treatment. The secretion of aldosterone, induced by angiotensin II, was not influenced by nicardipine treatment. No effect of the drug on adrenal responsiveness to angiotensin II was found.

Calcium channel blockers as antihypertensive agents

Because of their unique action on the cardiovascular system, the calcium channel blockers have generated a great deal of excitement among pharmacologists, physiologists, and clinicians. One obvious potential application for these drugs is in antihypertensive therapy and, although experience with these agents for this indication is limited in the United States, it is considerable in Europe and Japan. These agents' ultimate role in antihypertensive therapy, however, has not been established. Since the available calcium channel blockers are structurally diverse, it is uncertain whether they will have comparable effects in hypertension. The rationale for the use of calcium channel blockers in treating hypertension and the relevant pharmacologic actions of these agents is discussed, along with a summary of some of the clinical trials, observations from our own experience with these drugs, and speculation about their future role in antihypertensive therapy.

Antihypertensive and renal effects of nicardipine

Both the acute blood pressure lowering and renal effects of the calcium antagonist nicardipine and those after 1 week's treatment were investigated in 10 normotensive volunteers and in 10 patients with mild to moderate essential hypertension. After 1 week of placebo, nicardipine was administered orally for 1 week (20 mg three times daily), Investigations, done on the first and last day of nicardipine treatment were compared with those on the last day of placebo. During water loading, nicardipine increased urinary volume and urinary excretion of sodium significantly after 1 week nicardipine treatment. In the normotensive group the natriuretic effect was caused by a decrease of fractional proximal and distal reabsorption of sodium. In the hypertensive group the natriuresis was achieved mainly by an increase of the rate of glomerular filtration (GFR) and also by a slight distal effect. Our results show that nicardipine had natriuretic effects. There were trends suggesting that the renal effects may differ between patients with essential hypertension and normotensive volunteers, but the findings might also be related to differences in age between the groups.

Clinical features and management of nifedipine overdosage in a patient with renal insufficiency

Overdosage with 280 mg nifedipine, verified by plasma nifedipine levels, led in a 23-year-old female patient with advanced renal insufficiency to features of marked vasodilation. Despite profound hypotension and preexisting anemia, tissue perfusion was adequately maintained. Neither cardiac conductance disturbances nor myocardial depression occurred. There was no evidence for major organ or organ system toxicity. The patient was successfully treated with intravenous calcium. Hemoperfusion did not significantly influence the clinical course. The recovery was uneventful. No late sequelae were observed.

[Calcium antagonists in the therapy of hypertension]

Calcium antagonists (nifedipine, verapamil, diltiazem) are potent vascular smooth muscle relaxants. Experimental and clinical investigations provide growing evidence that they are effective in acute and (sub)chronic therapy of arterial hypertension by lowering peripheral vascular resistance and improvement of altered hemodynamics--independent from pathogenesis of hypertension. Due to its prompt and profound hypotensive action, sublingual or oral nifedipine has been used successfully in hypertensive crises. The hypotensive effect usually correlated closely with the severity of hypertension and is nearly absent in normotensive controls. Since the blood pressure drop may occasionally results in absolute or relative hypotension, the initial dose should be as low as possible. The activation of the adrenergic and renin angiotension systems seen after nifedipine administration is less pronounced after chronic administration of the drug and is nearly absent after verapamil and diltiazem. Plasma aldosterone concentrations remain constant or are slightly decreased. In contrast to classic vasodilators, the long-term administration of calcium antagonists usually does not result in tachycardia (nifedipine), but slight sinus bradycardia (verapamil, diltiazem). Peripheral edema may occasionally occur after nifedipine. A tolerance has been observed during long-term treatment of hypertension. Combining these drugs (verapamil, diltiazem) with betablockers is not recommended due to the negative inotropic and bathmotropic effects. Simultaneous administration of nifedipine and beta-blockers enhances the hypotensive action, but favours the development of peripheral edema and in rare cases (especially in severe coronary heart disease) results in a dramatic drop in blood pressure and/or congestive heart failure. Further clinical evaluation and long-term trials of calcium antagonists as antihypertensive agents will be needed before definite conclusions can be drawn.