Viagra et al
Posted on 21st November 2022 at 11:40
In the late 1980’s, Pfizer, an American pharmaceutical firm, were investigating the role of a new drug called sildenafil in cardiovascular disease. It was noted that a common side effect was an improvement in erectile dysfunction (ED). Perhaps not surprisingly, they diverted their further interest towards this. It might be an over-statement to say that Viagra (whoever named it clearly knew their Latin: life/vitality/strength/aggression) was a “game-changer” in the sense that penicillin, insulin, steroids, cimetidine were, but it has certainly had a huge impact on the self-esteem, well-being and relationships of millions of men around the world.
I want to discuss this and other drugs used in the management of ED. They are known as phosphodiesterase type 5 inhibitors (PDE5I). They dilate blood vessels (vasodilators: hence the original interest in cardiovascular disease) and, in ED, increase the blood flow to the penis. The wonderful thing about them is that they do this only with sexual stimulation: previously, drugs like alprostadil (injected into the penis) would produce an erection at the time.
Common side effects reflect the vasodilator effects: headaches, nasal congestion, colour disturbance. There are rare serious optical side-effects with all PDE5I: any significant visual disturbance should be reported and no PDE5I used again unless reassured by an ophthalmologist. Start on the lowest dose and increase as necessary. Refer back to physician if no response.
Sildenafil (originally Viagra, but now available generically): 25, 50 or 100mg. onset of action about 1 hour after ingestion (on an empty stomach). Lasts 8-10 hours.
Vardenafil (Levitra): 10 or 20 mg. Similar to sildenafil, but probably better. There was a 10mg orodispersible tablet available with a claimed 20 minute onset of action, so good for “quickies”, but this is no longer made. Lasts 8-10 hours. Not available generically at present.
Avanafil (Spedra): 50, 100 or 200mg. The most recent introduction. Claimed to have the quickest onset of action. Lasts 8-10 hours. Not available generically at present.
Tadalafil (Cialis, but now available generically). 5, 10 or 20mg. Slower onset of action, but 10-20mg dose lasts for 48-72 hours (the French call it “Le Weekend”). The interesting and important aspect of tadalafil is that it also seems to have beneficial effects on the cardiovascular system, the bladder and the prostate, and some urologists think it should be almost routinely prescribed 5mg daily to all gentleman of a certain age… but the NHS won’t. I will.
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