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NITRATES : CONTRAINDICATIONS and WARNINGS
* Hypersensitivity to nitrates (rare).
* Severe anemia (relative contraindication because vasodilation
will further increase the heart rate and may increase the
work of the heart).
* Hypotension, especially in myocardial infarction (because it
is suspected that further reduction in coronary perfusion
pressure may worsen cardiac ischemia).
* Brain injury, other conditions involving suspected increase in
intracranial pressure (because vasodilators may further in-
crease intracranial pressure).
* Arcing may occur when cardioversion is performed on a patient
with a transdermal nitroglycerine patch on the chest. Such
patches should be removed before applying the shock.(Warning)
* Syncope. (Warning) Postural hypotension may occasionally be
sufficient to cause syncope.
* Myocardopathy. (Warning) Nitrates may worsen angina in
patients with hypertrophic cardiomyopathy.
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ADVERSE REACTIONS AND OVERDOSE TOXICITY:
Severe toxicity is rare, even when these drugs are abused as
"recreational" (sex-enhancing) agents.
* CNS: A throbbing headache is common, especially if no
tolerance to the drug is present. Dizziness (probably due to
orthostatic hypotension) is often reported after large doses.
* CV: Mild-to-moderate orthostatic hypotension, caused by
peripheral venodilatation, is common. It is readily relieved
by sitting or lying down. Tachycardia is a common reflex
response to the hypotension. Gross overdosage may induce
severe hypotension, especially in susceptible individuals,
eg, those with hypovolemia. Associated symptoms, which are
usually transient, include dizziness, syncope, sweating,
tachycardia, nausea, and vomiting. Treatment, if necessary,
is by administration of vasoconstrictors, usually
* GI: Nausea and rarely, vomiting, may occur with ordinary
therapeutic use. Sublingual and buccal preparations often
cause a burning or tingling sensation in the mouth, and this
has been assumed to constitute a test of the "activity" of
the preparation. It is not a reliable test.
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* Skin: Hypersensitivity reactions may be induced by transdermal
preparations, perhaps caused by the vehicle and adhesives
that are present.
* Methemoglobinemia: Nitrites may cause methemoglobinemia at
moderate doses and this effect is common with overdoses. This
may be hazardous, especially in anemic individuals. It is
used therapeutically as an antidote in cyanide poisoning.
Nitrates rarely if ever cause methemoglobinemia, except in
unweaned infants. Severe methemoglobinemia is associated with
pseudocyanosis, acidosis, and other signs of tissue hypoxia.
Treatment is by slow IV administration of methylene blue, 1-2
* Hypotensive agents: Because they lack direct autonomic and me-
tabolic effects, the only significant interaction of the
nitrates is with other hypotensive agents, with which they
have additive or superadditive effects.
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