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)
  2. Men using nitrates (causes profound Hypotension)
  3. Men using alpha blockers (e.g. Hytrin for BPH)

VII. Mechanism

VIII. Drug Interactions

  1. See Phosphodiesterase Inhibitors (PDE5)
  2. Profound Vasodilitation and Hypotension with Nitroglycerin and alpha blockers such as Prazosin (Avoid)
  3. Cytochrome P3A4 related interactions (Cimetidine, systemic Antifungals, Protease Inhibitors and Macrolides

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

  1. See Phosphodiesterase Inhibitors (PDE5)
  2. Hypotensive effect for men on Nitrates (Avoid)
  3. Vision effects (color vision, Vision Loss)
  4. Sensorineural Hearing Loss
  5. Mild Headache

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Cost: Medications

viagra (on 6/1/2016 at Medicaid.Gov Survey of pharmacy drug pricing)
VIAGRA 100 MG TABLET $46.76 each
VIAGRA 25 MG TABLET $46.53 each
VIAGRA 50 MG TABLET $46.66 each
sildenafil (on 8/17/2016 at Medicaid.Gov Survey of pharmacy drug pricing)
SILDENAFIL 20 MG TABLET Generic $0.50 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