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Phosphodiesterase (PDE5) inhibitors in erectile dysfunction

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

In the UK the currently available phosphodiesterase (PDE5) inhibitors are sildenafil Viagra), tadalafil (Cialis) and vardenafil (Levitra)

mechanism of action:

  • PDE5 inhibitors prevent the degradation of cyclic GMP thereby prolonging production of the vasodilator nitric oxide. PDE5 inhibitors are only effective in the context of sexual arousal

dosing of PDE5 inhibitors:

  • doses may need to be titrated to achieve effect
    • the majority of diabetics need the maximum dose of PDE5 inhibitor to achieve effect (1)
    • PDE5 inhibitors may take several doses over time to work. The patient should be warned that he may need 8 attempts before a satisfactory erection occurs – at least 4 at the highest dose (1)

Adverse effects:

  • these occur secondary to smooth muscle relaxation and include headache, flushing and acid reflux but are not usually limiting
  • transient blue vision can occur with use of sildenafil

The respective summary of products must be consulted before prescribing any of the drugs mentioned.


  1. British Heart Foundation (factfile 6/2005).Drugs and Erectile Dysfunction.
  2. Prescriber (2003), 14 (20), 28-31.

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