Sildenafil
A short-acting PDE5 inhibitor used for erectile dysfunction and for pulmonary arterial hypertension.
Drug card
- Class
- PDE5 inhibitor
- How it works
- Blocking PDE5 so cGMP builds up and smooth muscle relaxes
- Used for
- Erectile dysfunction
- Pulmonary arterial hypertension (WHO group 1)
- Known for
- Headache
- Flushing
- Blue-green tinge, light sensitivity or blurred vision
- Its name
- -afil means a PDE5 inhibitor
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does sildenafil work?
Selective for PDE5, but only about 10 times weaker against PDE6 in the retina, which explains its blue-green color vision changes. Levels peak about an hour after a dose, later after a fatty meal. CYP3A4 clears it, with an active N-desmethyl metabolite, and both have half-lives of about 4 hours.
Like other 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.
Uses
What is sildenafil used for?
- Erectile dysfunction
- Pulmonary arterial hypertension (WHO group 1)
Side effects
Side effects of sildenafil
- HeadacheKnown for
- FlushingKnown for
- Blue-green tinge, light sensitivity or blurred visionKnown for
- Indigestion
- Fast or irregular heartbeatSerious
- Nosebleeds
- Low blood pressure, dangerous with nitratesSerious
- PriapismSerious
- Sudden loss of vision (NAION)Serious
- Sudden loss of hearingSerious
- SeizuresSerious
- Heart attack or stroke, reported mainly with heart diseaseSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated with nitrates in any form and with riociguat.
- Ritonavir and other strong CYP3A4 inhibitors raise its levels steeply; with an alpha blocker, start only once that is stable.
- Not recommended in retinitis pigmentosa or pulmonary veno-occlusive disease; take care after a past NAION.
- In pulmonary hypertension caused by sickle cell disease it led to more vaso-occlusive crises.
Good to know: Its 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.
Remember it
A way to remember it
FLUSH
- F
- Flushing of the face
- L
- Loss of vision or hearing, sudden and rare
- U
- Upset stomach (indigestion)
- S
- Stuffy nose
- H
- Headache
Written for biofideX
Its name
-afil means PDE5 inhibitor
Sildenafil, tadalafil and vardenafil block phosphodiesterase 5, which breaks down cGMP, so smooth muscle relaxes; erectile dysfunction is the best-known use.
- Every drug name stem
Its class
PDE5 inhibitors
Other PDE5 inhibitors with a card:
Easily mixed up with nitrates and methylxanthines.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Sildenafil citrate tablets for erectile dysfunction: label (DailyMed)
- Sildenafil tablets for pulmonary arterial hypertension: label (DailyMed)
- Sildenafil (NCI Thesaurus)
- Sildenafil (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.
Reproductive and urinary health
Sildenafil is one of 9 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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