Viagra

1. Indications
   1. Psychogenic Impotence
   2. Neurogenic Impotence
   3. Vasculogenic Impotence
2. Contraindications
   1. Absolute Contraindications
      1. Men using nitrates (causes profound Hypotension)
   2. Relative Contraindications
      1. Active coronary ischemia in men not on nitrates
      2. Congestive Heart Failure
         1. Borderline low Blood Pressure
         2. Bordrline low volume status
      3. Multidrug antihypertensive regimen
      4. Taking Cytochrome P450-3A4 (CYP3A4) inhibitor
   3. Areas where Sildenafil may be used safely
      1. Safe in stable coronary disease (no nitrates)
         1. Debusk (2004) Am J Cardiol 93:147-53
3. Mechanism
   1. Phosphodiesterase Type 5 Inhibitor
      1. Phosphodiesterase Type 5 causes Erection to subside
   2. Viagra blocks Phosphodiesterase Type 5
      1. Results in enhanced Erection if man is aroused
      2. Unlike Alprostadil, will not cause Erection
   3. Viagra enhances vasodilating effect of Nitrous Oxide
      1. Normally released during sexual stimulation
4. Pharmacokinetics
   1. Peak: 1 hour if taken while fasting
      1. Peak delayed by 1 hour if taken with fatty meal
   2. Half Life: 4 hours
   3. Metabolized by Liver and excreted mostly in stool
      1. Clearance delayed in age over 65 years
      2. Clearance delayed in Liver disease
5. 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
6. Efficacy
   1. Benefits those with organic and psychological Impotence
   2. Initial studies showed improved Erections in 70%
   3. Over Placebo, 3.6 times more likely to improve Erection
      1. Burls (2001) Br J Gen Pract 51:1004-12
7. Drug Interactions
   1. Inhibit breakdown of Viagra via Cytochrome P3A4
      1. Cimetidine (Tagamet)
      2. Erythromycin
      3. Ketoconazole (Nizoral)
      4. Itraconazole (Sporonox)
      5. Mibefradil (Posicor)
   2. Profound Vasodilitation and Hypotension (Avoid)
      1. Nitrates
8. Adverse Effects
   1. Hypotensive effect for men on Nitrates (Avoid)
   2. Vision effects
      1. Temporary color vision disturbance (6%)
         1. Blue colors may appear to be green
      2. Blurred vision or Vision Loss
         1. Higher risk if atherosclerosis
         2. Rare occurence, but can be permanent
         3. Appears to occur with Levitra and Cialis as well
   3. Mild Headache (21%)
   4. Facial Flushing (27%)
   5. Indigestion or Dyspepsia (11%)
   6. Does not cause Priapism
   7. Sensorineural Hearing Loss
      1. Sudden onset and permanent Hearing Loss
      2. McGwin (2010) Arch Otolaryngol Head Neck Surg 136(5):488-49
9. Cost
   1. Wholesale: $7 per pill
10. Reference
    1. Boolell (1996) Br J Urol 78:257-61
    2. Cheitlin (1999) J Am Coll Cardiol 33:273-82
    3. (1998) Med Lett Drugs Ther 40(1026):51-2
    4. Rendell (1999) JAMA 281(5): 421-26