Name: Verapamil (Calan)
Class: Calcium-Entry Blocking Agent (Antidysrhythmic Agent Class IV)
Mechanism: Binds to L-type Ca2+ channels ® ¯ Ca2+ in arterial smooth muscle cells ® vasodilation ®
¯ cardiac afterload. Little/no effect on venous vessels. ¯ inotropy, chronotropy, & dromotropy.
Net = ¯ HR, ¯ conduction, ¯ contractility, ¯ BP. May inhib. platelet aggreg.
Absorption: Oral ® nearly complete absorption. 1st pass Metabolism®¯ bioavail. IV.
Dist.: Significant protein binding.
Metabolism.: Hepatic. Inducible Metabolism. Inhibits hepatic enzymes. Active Metabolismolites.
Excretion, t½: 1.5-6 hr. Repeated oral dose ® t½ due to hepatic saturation. Longer t½ in elderly or pts w/hepatic cirrhosis or renal insuff.
Toxicity/S.E.s: Dizziness, hypotension, headache, constipation, gingival hyperplasia, flushing, edema. Aggravation of myocardial ischemia (less than w/DHPs). Serious toxicities (bradycardia, transient asystole, exacerbation of heart failure) are rare, but may occur after IV admin; coadmin w/b-blocker (c/i); or in pts. w/ventricular dysfxn, conduction disturbances, or systolic BP < style=""> digoxin levels. C/i w/CHF, quinidine.
Utility: Rx angina (stable, variant, unstable), arrhythmias, hypertension. More effective than propranolol for unstable angina. DOC (IV) for paroxysmal supraventricular tachycardias. Reentry arrhythmias.
Special Features: Blocking action is frequency and voltage dependent. \ more effective in rapidly depolarizing cells. At vasodilatory doses, greater negative chronotropic, dromotropic, and inotropic effects than the dihydropyridines. Greatest effect on heart of channel blockers.