Phosphodiesterase type V inhibitors

Phosphodiesterase type V (PDE5) inhibitors are used in the treatment of erectile dysfunction. They are also used in the management of pulmonary hypertension. PDE5 inhibitors cause vasodilation through an increase in cGMP leading to smooth muscle relaxation in blood vessels supplying the corpus cavernosum.

Examples

• sildenafil (Viagra)
  • this was the first phosphodiesterase type V inhibitor
  • short-acting - usually taken 1 hour before sexual activity
• tadalafil (Cialis)
  • longer acting than sildenafil, may be taken on a regular basis (e.g. once daily)
• vardenafil (Levitra)

Contraindications

• patients taking nitrates and related drugs such as nicorandil
• hypotension
• recent stroke or myocardial infarction (NICE recommend waiting 6 months)

Side-effects

• visual disturbances
  • blue discolouration
  • non-arteritic anterior ischaemic neuropathy
• nasal congestion
• flushing
• gastrointestinal side-effects
• headache
• priapism

The blue pill, Viagra (sildenafil), causes blue discolouration of vision