Drug Classification:
Viagra® (sildenafil citrate) is a type 5 phosphodiesterase (PDE5) inhibitor. It was discovered and developed by Pfizer, Inc. for the treatment of male erectile dysfunction. Sildenafil citrate is an oral agent that works indirectly to enhance the relaxation of vascular smooth muscle in the arterioles and sinusoids of the corpus cavernosum.
Effective erection involves the release of neurotransmitters by nerves that act on the corpora cavernosa of the penis. These neurotransmitters, including nitric oxide (NO), activate the enzyme guanylate cyclase which increases the level of cyclic Guanosine Monophosphate (c-GMP) within the cells of the corpus cavernosum. Accumulation of c-GMP within the smooth muscle cells of the corpus cavernosum decreases arteriovascular tone which enhances arterial blood flow into the corpus cavernosum.
Viagra® interferes with the normal enzymatic breakdown of c-GMP by blocking the action of type 5 phosphodiesterase (PDE5). Type 5 phosphodiesterase is an enzyme that turns c-GMP into the inactive molecule GMP.
(cGMP) is a common intracellular molecule that is involved in many cell processes including: regulation of ion channels and smooth muscle relaxation. Blocking the enzymatic degradation of c-GMP in the corpus cavernosum results in prolonged smooth muscle relaxation, arterial dilation and improved engorgement.
Please access Pfizer's website on Viagra to review the mechanism of action for this drug, and then answer the Instant Feedback question below.
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