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Normal penile erection depends on the relaxation of smooth muscles in the corpora cavernosa. In response to sexual stimuli, cavernous nerves and endothelial cells release nitric oxide, which stimulates the formation of cyclic guanosine monophosphate (GMP) by guanylate cyclase. Sildenafil Citrate is a selective potent inhibitor of GMP in the corpus cavernosum and therefore increases the penile response to sexual stimulation. (NEJM 338:1397-1404 May 1978) Sildenafil Citrate is rapidly absorbed, with maximal plasma concentrations occurring between one and four hours after oral administration depending upon gastric emptying which can be slowed by food or alcohol intake. A portion of the Sildenafil Citrate is absorbed through the portal vein in the intestinal tract and is degraded in the first pass through the liver. Sildenafil Citrate in a gelatin-based troche placed under the tongue and is believed to be absorbed directly into the blood stream through the buccal mucosa without the "first pass" through the liver. Sildenafil Citrate in the soft tab form is not subject to the variability of absorption due to gastric emptying, and has a faster onset of action — perhaps within 15 to 30 minutes.
Sildenafil Citrate has been reported to significantly improve both subjective and physiologic parameters of the female sexual response in women with sexual arousal disorders. Further study is underway. (Berman, et. al., New Perspectives in the Management of Female Sexual Dysfunction, Boston, October, 1999), Sildenafil Citrate should not be taken by patients who take medicines containing nitrates. If a patient is taking any nitrate drug such as Isordil, Nitropaste, Nitropress, Nitrostat, or Nitroglycerin, they cannot take Sildenafil Citrate.
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