Viagra

Aka: Viagra, Sildenafil

1. Indications
   1. Psychogenic Impotence
   2. Neurogenic Impotence
   3. Vasculogenic Impotence
2. 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
3. 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
4. Cost
   1. Wholesale: $7 per pill
5. Contraindications
   1. See Phosphodiesterase Inhibitors (PDE5)
   2. Men using nitrates (causes profound Hypotension)
   3. Men using alpha blockers (e.g. Hytrin for BPH)
6. Mechanism
   1. See Phosphodiesterase Inhibitors (PDE5)
7. 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
8. 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
9. 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]