ACTIONS AND PHARMACOLOGY This dihydropyridine calcium-channel antagonist has been one of the most extensively studied agents for rapid control of blood pressure. Until the last few years when awareness of serious side effects became more widespread, it had been the most frequently used agent for acute blood pressure lowering in hospitalized patients. It is a coronary and peripheral arterial dilator, which causes a slight increase in heart rate but rarely causes postural hypotension. It can be given orally, sublingually, or rectally and has been shown to lower blood pressure quickly and in a rapid dose-dependent manner. After sublingual administration, the onset of action is 1 to 5 min, with a maximal effect at 20 to 60 min. The duration of action is 3 to 5 h. The clearance half-life is 2 to 4 h and the time to peak level remains constant with all doses. It undergoes extensive hepatic metabolism.
With an oral dose, peripheral vascular resistance falls, cardiac output increases, and pulmonary capillary wedge pressures decrease. There is a slight increase or no change in the glomerular filtration rate and renal blood flow. Nifedipine may improve cardiac performance in patients with impaired ventricular function but, because of its negative inotropic effect, should be used with caution in patients with severe congestive heart failure.
INDICATIONS The US Food and Drug Administration (FDA) has never specifically approved the use of short-acting nifedipine for the treatment of hypertension of any kind. Because of the risks of serious adverse reactions, such as acute coronary events or an ischemic stroke, the US National Heart, Lung, and Blood Institute issued a warning in 1995 stating that this agent should not be used in the treatment of hypertension, angina, and myocardial infarction. 21 The extended-release form of nifedipine appears to have less adverse effects than the short-acting formulations.
SIDE EFFECTS AND CONTRAINDICATIONS The common side effects of flushing, headache, pedal and periorbital edema formation, and palpitations are relatively well tolerated. The less common, but more serious, complications that have occurred include cerebral ischemia, syncope, complete heart block, symptomatic hypotension, sinus arrest, retinal ischemia, congestive heart failure, and myocardial ischemia/infarction. Rebound hypertension can also occur when nifedipine therapy is stopped abruptly.
Although nifedipine has been used widely for hypertensive urgencies, some patients are predisposed to unfavorable outcomes with the use of this drug. Five effects have been identified that can cause complications when nifedipine is used to treat acute hypertension in some vulnerable patient populations. 22 These are (1) proischemic effects—the potential to worsen ischemia unpredictably, especially in areas of the myocardium with good collaterals, (2) prohemorrhagic effects—antiplatelet activity combined with vasodilation, (3) negative inotropy—especially in patients with a history of congestive heart failure, (4) hypotension—with resultant hypoperfusion of the subendocardium, and (5) arrhythmogenic effects—predisposition to ventricular tachyarrhythmias in some populations.
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