Back one screen: left arrow Back to main menu: ESC II. NITRATES Pharmacokinetics (see also

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Back one screen: left arrow Back to main menu: ESC II. NITRATES Pharmacokinetics (see also Table ) * Absorption: fast and short acting (sublingual, 15-30 min dura- tion), intermediate (oral or buccal, 2-4 hr), and long acting (transdermal, 4-8 hr). * Active parent drugs are rapidly metabolized in the liver and elsewhere and have half-lives of only 2-8 minutes. Longer ac- tion is achieved by either overwhelming the first pass hepatic enzymes (oral forms of the drugs) or providing for very slow absorption into the systemic circulation from a large reservoir (buccal and transdermal forms). It is believed that much of the action of the longer-acting forms is due to active metabolites. * The intravenous form of nitroglycerine is used only in un- stable angina and in severe congestive heart failure. (PgDn key for more text) Other indications for the nitrates: * Smooth muscle relaxation: The nitrates are occasionally used to relax the ureter in renal colic and the common duct in biliary colic; efficacy is very low. * Methemoglobin production by nitrites: Methemoglobin, which can be produced by nitrites, has a high affinity for cyanide and is part of the antidote used in cyanide poisoning (see Chap- ter 24). Drugs of Special Importance * Nitroglycerine is the prototype nitrate and available in many dosage forms. Substitutes are rarely needed. * Isosorbide dinitrate is the most popular substitute nitrate. * Nitrites, eg, amyl nitrite, are obsolete and should not be prescribed in angina. Amyl nitrite is still used as a temporary measure in the treatment of cyanide poisoning. Sodium nitrite is a more effective antidote for cyanide (see antidotes, Chapter 24). Several organic nitrites, including amyl and isobutyl nitrite, have been fad recreational drugs, supposedly providing "sex enhancement." Related Drugs: * Dipyridamole, not a nitrate compound, was promoted for use in angina. It is no longer labeled for this application. (Home to return to top of file)


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