Headache which may be severe and persistent may occur immediately after use. Vertigo, dizziness, weakness, palpitation, and other manifestations of postural hypotension may develop occasionally, particularly in erect, immobile patients. Marked sensitivity to the hypotensive effects of nitrates (manifested by nausea, vomiting, weakness, diaphoresis, pallor, and collapse) may occur at therapeutic doses. Syncope due to nitrate vasodilatation has been reported. Flushing, drug rash, and exfoliative dermatitis have been reported in patients receiving nitrate therapy.

Patients receiving antihypertensive drugs, beta-adrenergic blockers, or phenothiazines and nitrates should be observed for possible additive hypotensive effects. Marked orthostatic hypotension has been reported when calcium channel blockers and organic nitrates were used concomitantly.

Concomitant use of nitrates and alcohol may cause hypotension.

The vasodilatory and hemodynamic effects of nitroglycerin may be enhanced by concomitant administration of aspirin.

Intravenous administration of nitroglycerin decreases the thrombolytic effect of alteplase. Therefore, caution should be observed in patients receiving sublingual nitroglycerin during alteplase therapy.

Intravenous nitroglycerin reduces the anticoagulant effect of heparin and activated partial thromboplastin times (APTT) should be monitored in patients receiving heparin and intravenous nitroglycerin. It is not known if this effect occurs following single sublingual nitroglycerin doses.

Tricyclic antidepressants (amitriptyline, desipramine, doxepin, others) and anticholinergic drugs may cause dry mouth and diminished salivary secretions. This may make dissolution of sublingual nitroglycerin difficult. Increasing salivation with chewing gum or artificial saliva products may prove useful in aiding dissolution of sublingual nitroglycerin.

Oral administration of nitroglycerin markedly decreases the first-pass metabolism of dihydroergotamine and subsequently increases its oral bioavailability. Ergotamine is known to precipitate angina pectoris. Therefore, patients receiving sublingual nitroglycerin should avoid ergotamine and related drugs or be monitored for symptoms of ergotism if this is not possible.

Administration of nitroglycerin is contraindicated in patients who are using Viagra (sildenafil citrate). Viagra has been shown to potentiate the hypotensive effects of organic nitrates.

A decrease in therapeutic effect of sublingual nitroglycerin may result from use of long- acting nitrates.

Drug/Laboratory Test Interactions: Nitrates may interfere with the Zlatkis-Zak color reaction causing a false report of decreased serum cholesterol.

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