Directly acting vasodilators
DIRECTLY ACTING VASODILATORS
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Directly acting vasodilators produce their action mainly by interfering with the availability of calcium for vasoconstriction.
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Calcium entry is prevented either by blocking voltage dependent Ca2+ channels or by causing hyperpolarization.
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Drugs produce vasodilator activity by altering Ca2+ release from the sarcoplasmic reticulum or reuptake into it and enzymes that determine Ca2+ sensitivity.
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These mechanisms are exemplified by calcium antagonists, potassium channel activators and drugs that influence cytoplasmic concentrations of cyclic neucleotides.
Nitrates
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Amyl nitrate, isosorbide dinitrate, glyceryl trinitrate ( nitroglycerine) are used as vasodilators.
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These are available as oral tablets, buccal tablets, sublingual tablets, inhalation preparations, topical patches (sustained release) and topical ointment.
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Nitroglycerine also helps to dilate coronary blood vessels.
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These drugs cause a direct relaxation of arterial and venous smooth muscles by acting as a source of nitric oxide which is released and causes direct relaxation.
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Toxicity includes hypotension, methemoglobinaemia and dermatitis.
Calcium channel blockers
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These drugs cause generalized vasodilatation, though individual agents differ in regional distribution of the effect by reducing intracellular availability of Calcium ions.
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Drugs under this category include verapamil, diltiazem, nifedipine, nimodipine and amlodipine.
Potassium channel activators
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These drugs relax smooth muscles by selectively increasing the membrane permeability to K+.
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This hyperpolarizes the membrane, switching off voltage dependent Ca2+ channels and inhibiting action potential generation.
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Drugs under this category include cromokalin, pinacidil, minoridil and diazoxide.
Agents that act by increasing cyclic nucleotide concentration
Vasodilators with unknown mechanism of action
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Last modified: Wednesday, 25 April 2012, 11:38 AM