Nitroglycerin relaxes the vascular smooth muscle. Although the precise details remain unclear, the direct effect on vascular smooth muscle appears to be the result of liberation of free radicals of nitric oxide (NO) which activates guanylate cyclase, resulting in increased synthesis of cyclic GMP. It is possible that nitric oxide (NO) combines with sulfhydryl groups in the endothelium and produces S-nitrosothiols that stimulate guanylate cyclase production. This is enhanced by N-acetylcysteine which provides a source of sulfhydryl groups. Cyclic GMP reduces stored calcium and thus interferes with calcium-activated smooth muscle contraction.
During an anginal attack, one or two sprays should be administered under tongue. The medication should not be expectorated or the mouth rinsed for 5 to 10 minutes following administration. A spray may be repeated approximately every 3-5 minutes as needed. No more than three metered sprays are recommended within a 15-minute period. If chest pain persists, prompt medical attention is recommended. Nitrocard spray may be used 5 to 10 minutes prior to engaging in activities which might provoke an acute attack.