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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-
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."
* Dipyridamole, not a nitrate compound, was promoted for use in
angina. It is no longer labeled for this application.
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