The agents commonly called the calcium channel blockers comprise an increasing number of agents, including the prototypical verapamil (Calan, Isoptin), nifedipine (Adalat, Procardia), and diltiazem (Cardizem). These agents are a chemically and pharmacologically heterogeneous group of synthetic drugs, but they possess the common property of selectively antagonizing Ca++movements that underlie the process of excitation contraction coupling in the cardiovascular system. The primary use of these agents is in the treatment of angina, selected cardiac arrhythmias, and hypertension.
Although the Ca++ channel blockers are potent vasodilating drugs, they lack the fluidaccumulating properties of other vasodilators and the persistent activation
of the sympathetic and renin–angiotensin–aldosterone axes. Furthermore, the broad potential range of activities, both within and without the cardiovascular system,
suggests that they may be clinically useful in disorders from vertigo to failure of gastrointestinal smooth muscle to relax .
A number of second-generation analogues are known, particularly in the nifedipine (1,4-dihydropyridine) series, including nimodipine (Nimotop), nicardipine (Cardene), felodipine (Plendil), nisoldipine (Sular), and amlodipine (Norvasc). These agents differ from nifedipine principally in their potency, pharmacokinetic characteristics, and selectivity of action.Nimodipine has selectivity for the cerebral vasculature; amlodipine exhibits very slow kinetics of onset and offset of blockade;and felodipine and nisoldipine are vascular-selective 1,4-dihydropyridines.
Adverse reactions
Adverse reactions to the calcium channel blocking drugs usually are not serious and rarely require discontinuation of the drug therapy. The more common adverse reactions include dizziness, light-headedness, nausea,diarrhea, constipation, peripheral edema, headache,
bradycardia, flushing, dermatitis, skin rash, and nervousness. Antianginal
Drugs for a more specific listing of the adverse reactions
of the calcium channel blockers.
Contraindicated
Calcium channel blockers are contraindicated in patients who are hypersensitive to the drugs and those with sick sinus syndrome, second- or third-degree AV block (except with a functioning pacemaker), hypotension (systolic less than 90 mm Hg), ventricular dysfunction,
or cardiogenic shock. The calcium channel blockers are used cautiously during pregnancy (Pregnancy Category C) and lactation and in patients with congestive heart
failure (CHF), hypotension, or renal or hepatic impairment.
The effects of the calcium channel blockers are increased when administered with cimetidine or ranitidine. A decrease in effectiveness of the calcium channel blockers may occur when the agents are administered with phenobarbital or phenytoin. The calcium channel blockers have an antiplatelet effect (inhibition of platelet function) when administered with aspirin, causing easy bruising, petechiae (pin point purplish red spot caused by intradermal hemorrhage), and bleeding. There is an additive depressive effect on the myocardium when the calcium channel
blockers are administered with the -adrenergic blocking drugs. When the calcium channel blockers are administered with digoxin, there is an increased
risk for digitalis toxicity.
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Unknown - Thursday, 23 December 2010
