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Viagra, Sildenafil

  • See Also
  1. PDE5 Inhibitor
  2. Vardenafil (Levitra, Staxyn)
  3. Tadalafil (Cialis)
  • Indications
  1. Psychogenic Impotence
  2. Neurogenic Impotence
  3. Vasculogenic Impotence
  • 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
  • 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
  • Cost
  1. Wholesale: $7 per pill
  • Contraindications
  1. See Phosphodiesterase Inhibitors (PDE5 Inhibitors)
  2. Men using nitrates (causes profound Hypotension)
  3. Men using alpha blockers (e.g. Hytrin for BPH)
  • Mechanism
  1. See Phosphodiesterase Inhibitors (PDE5 Inhibitors)
  • 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
  • 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
  • Reference
  1. Boolell (1996) Br J Urol 78:257-61 [PubMed]
  2. Cheitlin (1999) J Am Coll Cardiol 33:273-82 [PubMed]
  3. (1998) Med Lett Drugs Ther 40(1026):51-2 [PubMed]
  4. Rendell (1999) JAMA 281(5): 421-26 [PubMed]