II. Indications

  1. Psychogenic Impotence
  2. Neurogenic Impotence
  3. Vasculogenic Impotence

III. Pharmacokinetics

  1. Onset 30-60 minutes
  2. Duration: 4-5 hours
  3. Peak: 1 hour if taken while Fasting
    1. Peak delayed by 1 hour if taken with fatty meal
  4. Half Life: 4 hours
  5. Metabolized by Liver and excreted mostly in stool
    1. Clearance delayed in age over 65 years
    2. Clearance delayed in Liver disease

IV. Dosing

  1. Start 50 mg PO 1 hour before intercourse
    1. Do not take more than once per day
    2. Most insurance limits to 6 per month
  2. Indications to start with half dosing (25 mg)
    1. Age over 65 years
    2. Hepatic Impairment
    3. Renal Impairment
  3. Consider crushing tablet and placing under Tongue
    1. May increase onset of action to 15 minutes
    2. May also increase absorption
      1. Consider lowering dose

V. Cost

  1. Wholesale: $7 per pill

VI. Contraindications

  1. See Phosphodiesterase Inhibitors (PDE5 Inhibitors)
  2. Men using nitrates (causes profound Hypotension)
  3. Men using alpha blockers (e.g. Hytrin for BPH)

VIII. Drug Interactions

  1. See Phosphodiesterase Inhibitors (PDE5 Inhibitors)
  2. Profound Vasodilitation and Hypotension
    1. Nitroglycerin (Avoid within 24 hours of Sildenafil)
    2. Alpha blockers (e.g. Prazosin, Tamsulosin)
      1. Use with PDE5 Inhibitors only with caution when on these agents
  3. Cytochrome P3A4 related interactions (Cimetidine, systemic Antifungals, Protease Inhibitors and Macrolides

IX. Adverse Effects: Viagra (but most apply to the PDE5 Inhibitors as a whole)

  1. See Phosphodiesterase Inhibitors (PDE5 Inhibitors)
  2. Hypotensive effect for men on Nitrates (Avoid)
  3. Vision effects
    1. Photophobia (transient, common)
    2. Color Visiion Changes (e.g. blue-green tint, which is common and transient)
    3. Serious Vision changes (occur in up to 16 in 10,000 patients per year)
      1. See PDE5 Inhibitor
      2. Retinal Detachment
      3. Optic Neuropathy
  4. Sensorineural Hearing Loss
  5. Mild Headache

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Related Studies

Cost: Medications

viagra (on 6/1/2017 at Medicaid.Gov Survey of pharmacy drug pricing)
VIAGRA 100 MG TABLET $59.10 each
VIAGRA 25 MG TABLET $59.30 each
VIAGRA 50 MG TABLET $58.73 each
sildenafil (on 5/17/2017 at Medicaid.Gov Survey of pharmacy drug pricing)
SILDENAFIL 20 MG TABLET Generic $0.33 each

Ontology: sildenafil (C0529793)

Definition (CHV) a drug for male impotence
Definition (NCI_NCI-GLOSS) A drug used to treat erectile dysfunction. Sildenafil relaxes the smooth muscle of the penis to allow increased blood flow and erection. It is a type of phosphodiesterase inhibitor.
Definition (PDQ) The citrate salt of a pyrazolopyrimidinone derivative structurally related to zaprinast. Sildenafil selectively inhibits cyclic guanosine monophosphate (cGMP)-specific type 5 phosphodiesterase, resulting in vasodilation in the corpus cavernosum of the penis and penile erection. Check for "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=269137&idtype=1" active clinical trials or "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=269137&idtype=1&closed=1" closed clinical trials using this agent. ("http://nciterms.nci.nih.gov:80/NCIBrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&code=C26670" NCI Thesaurus)
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH C101426
SnomedCT 109123009, 372572000
English sildenafil, sildenafil [Chemical/Ingredient], SILDENAFIL, Sildenafil, Sildenafil (product), Sildenafil (substance)
Spanish sildenafilo, sildenafil, sildenafilo (producto), sildenafil (producto), sildenafilo (sustancia), sildenafil (sustancia)

Ontology: Viagra (C0663448)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH C101426
English Viagra, Abbott brand of sildenafil citrate, Pfizer brand 1 of sildenafil citrate