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Sildenafil

Basic information Uses Indications and Usage Adverse Reactions Safety Related Supplier
Sildenafil Basic information
Sildenafil Chemical Properties
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Sildenafil Usage And Synthesis
  • Uses

    Sildenafil, the first US FDA-approved, oral phosphodiesterase type-5 inhibitor, has revolutionized the treatment of erectile dysfunction sine its approval in 1998. Since sildenafil is a potent inhibitor of cyclic guanosine monophosphate in the corpus cavernosum and therefore increases the penile response to sexual stimulation.

  • Indications and UsageSildenafil Citrate is an oral drug used to treat male erectile dysfunction and is a 5-phosphodiesterase inhibitor developed by the American Pfizer Pharmaceuticals to originally treat cardiovascular disease that was later discovered to improve patients’ sex lives. Sildenafil Citrate treats erectile dysfunction and was the first clinical oral drug used to specifically target male erectile dysfunction.
  • Adverse ReactionsCommon adverse reactions include headache, dizziness, facial flushing, indigestion, nasal congestion, and sight abnormalities, which may be expressed as difficulty differentiation blue/green colors, light sensitivity, or blurry vision. More severe adverse effects include decreased supine blood pressure and decreased cardiac output. Additionally, clinical research shows that engaging in sexual activity after taking Sildenafil Citrate increases the risk of heart abnormalities, including angina pectoris, dizziness, nausea, and other symptoms, and it may also cause sudden cardiac death.
  • DescriptionSildenafil was launched as Viagra in the US for the treatment of organic orland psychological male erectile dysfunction (ED). Sildenafil can be obtained by functional rearrangement of the corresponding 5-aryl 1,3-dialkyl pyrazolo[4,3- d]pyrimidin-7-one, itself synthesized in a seven-step sequence from a pyrazole- 5-carboxylate. Sildenafil is a potent and selective inhibitor of type V cGMP phosphodiesterases (PDE5) ; IC50 = 3nM on isozymes from human corpus cavernosum tissue. This orally-active therapy is completely new and presents advantages over the classically recommended options such as vacuum constriction devices, drug injection or prosthesis implantation ; for these reasons, this first drug is likely to have a large acceptance fot the treatment of male ED. In experiments with incubated rabbit penile tissue, Sildenafil was shown to cause accumulation of cGMP. By inhibiting the enzyme PDE5, the predominant isozyme in the corpus cavernosum, Sildenafil induces an elevation of levels of second messager cGMP, which is involved in the regulation of vascular tone ; it was suggested that the specific elevation of cGMP due to Sildefanil would mediate an enhancement of nitric oxide-dependent relaxation of corpus cavernosal tissue. Several clinical studies using 10-100 mg Sildenafil have confirmed a good effectiveness and tolerability in healthy males. New trials in women with sexual disfunction have been initiated and positive results could enlarge the potential market of this drug.
  • Chemical PropertiesWhite Solid
  • OriginatorPfizer (UK)
  • Usesantiviral
  • UsesAn orally active selective type 5 cGMP phosphodiesterase inhibitor.
  • DefinitionChEBI: A pyrazolo[4,3-d]pyrimidin-7-one having a methyl substituent at the 1-position, a propyl substituent at the 3-position and a 2-ethoxy-5-[(4-methylpiperazin-1-yl)sulfonyl]phenyl group at the 5-position.
  • IndicationsSildenafil (Viagra) is a selective inhibitor of PD-5, an enzyme that inactivates cGMP. Vardenifil (Levitra) is a particularly effective inhibitor of PD-5. It has a shorter onset of action and can be used in smaller doses than sildenafil. Other drugs used in the treatment of ED exert their effects through other biochemical pathways, both central and peripheral.
  • IndicationsSildenafil (Viagra) was developed more than 10 years ago as an antihypertensive and antianginal drug. It proved ineffective in these applications but was shown to affect the smooth muscles of the penis.
  • brand nameViagra (Pfizer);Segurex.
  • Mechanism of actionSildenafil is readily absorbed after oral administration and reaches peak plasma levels after about an hour. It undergoes hepatic metabolism and has a terminal half-life of about 4 hours.An initial dose of 50 mg is taken about an hour prior to sexual activity to induce penile erection.
  • Clinical UseSildenafil is a selective inhibitor of cGMP-specific PD-5 and therefore inhibits the degradation of cGMP. PD-5, the predominant type in the corpus cavernosum, also is present in other tissues (e.g., lungs, platelets, and eye). The selective inhibition of this enzyme facilitates the release of nitric oxide and smooth muscle relaxation of the corpus cavernosa. Sildenafil enhances erection by augmenting nitric oxide–mediated relaxation pathways. It has been suggested that sildenafil’s mechanism of action is due to cross-talk between cGMP- and cAMPdependent transduction pathways within the cavernous muscles.
  • Side effectsOrally administered sildenafil is an effective and well-tolerated treatment for men with ED, including those with diabetes mellitus. It has also been used for so-called salvage therapy in men who do not respond to intracorporeal injections of other agents. Headache is a common side effect, as are flushing and rhinitis.More serious side effects include definite or suspected myocardial infarctions and cardiac arrest.
  • Enzyme inhibitorSildenafil is rapidly absorbed and peaks in concentration (127–560 ng/mL) after 0.5 to 2.0 hours, displaying a half-life of 3 to 4 hours for the full therapeutic dose (25–100 mg). It is 96% bound to plasma proteins and is metabolized by the liver CYP3A4. The metabolite N-desmethylsildenafil possesses approximately 50% of the activity of the parent molecule.
  • Metabolism In vitro metabolism studies for sildenafil have shown that the primary metabolite, N-desmethylsildenafil, and the minor metabolite, oxidative opening of the piperazine ring, are mediated by CYP3A4, CYP2C9, CYP2C19, and CYP2D6. The estimated relative contributions to clearance were 79% for CYP3A4, 20% for CYP2C9, and less than 2% for CYP2C19 and CYP2D6. These results demonstrate that CYP3A4 is the primary cytochrome mediating N-demethylation and that drugs inhibiting CYP3A4 likely impair sildenafil biotransformation and clearance. The pharmacokinetics of radiolabeled sildenafil were consistent with rapid absorption, first-pass metabolism, and primarily fecal elimination of N-demethylated metabolites. The absorption of sildenafil following oral administration was rapid (~92%), whereas the oral bioavailability was approximately 38% as a result of first-pass metabolism.
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