PDE5 inhibitors

They inhibit phosphodiesterase type 5, the enzyme that breaks down cGMP in smooth muscle. During sexual stimulation nitric oxide raises cGMP in the corpus cavernosum; with PDE5 blocked, cGMP lasts longer, the muscle relaxes and blood flows in, but nothing happens without stimulation. The same effect widens the pulmonary arteries and reaches the smooth muscle of the prostate and bladder.

• SildenafilIts low selectivity over retinal PDE6 (about 10-fold, against about 700-fold for tadalafil) is why blue-green color vision changes are typical of sildenafil.
• TadalafilIts long half-life gives a window of up to 36 hours and allows once-daily use for BPH; it is the only PDE5 inhibitor here licensed for BPH.

• Erectile dysfunction
• Pulmonary arterial hypertension
• Urinary symptoms of BPH (tadalafil)

• HeadacheKnown for
• Flushing of the faceKnown for
• Blue-tinged or blurred visionKnown for
• Indigestion
• Stuffy nose
• Muscle aches and back pain
• Low blood pressure, dangerous with nitratesSerious
• PriapismSerious
• Sudden loss of vision (NAION)Serious
• Sudden loss of hearingSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Never with nitrates in any form or with riociguat: blood pressure can fall dangerously.
• Not for men whose heart disease makes sexual activity unsafe; take care with alpha blockers and other antihypertensives.
• CYP3A4 inhibitors such as ritonavir raise their levels sharply.
• An erection lasting over 4 hours, or a sudden loss of vision or hearing, needs urgent assessment.

Written for biofideX in plain words, after checking these references:

• Sildenafil citrate tablets for erectile dysfunction: label (DailyMed)
• Tadalafil tablets: label (DailyMed)
• Sildenafil tablets for pulmonary arterial hypertension: label (DailyMed)
• cGMP phosphodiesterase inhibitor (NCI Thesaurus)
• Sildenafil (NHS)
• Tadalafil (NHS)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.