Phosphodiesterase inhibitors and alpha blockers

Sildenafil, tadalafil and vardenafil (the currently available PDE5 inhibitors in the UK) may all interact with non selective alpha blockers, e.g. doxazosin leading to orthostatic hypotension

• likelihood of such an interaction depends on the half life and dose of the PDE5 inhibitor
  • thus there is no interaction between alpha blockade and sildenafil 25 mg - however alpha blockers should not be taken within 4 hours of higher doses of sildenafil (50-100 mg)
  • alpha blockers should not be taken within 6 hours of vardenafil
  • alpha blockers should not be taken within 48 hours of tadalafil

No interactions have been recorded with the selective alpha blocker tamsulosin.

The respective summary of product characteristics must be consulted before prescribing any of the drugs mentioned

Reference:

1. British Heart Foundation (factfile 6/2005).Drugs and Erectile Dysfunction.