New erectile dysfunction drug has interaction with HIV protease inhibitors

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Cialis (tadalafil), the recently licensed anti-impotence drug, should be used with caution by men taking protease inhibitors, according to the patient information leaflet issued with the medicine by its manufacturer, Lilly.

Large numbers of men with HIV experience erectile problems, and the existing erectile dysfunction treatment, Viagra (sildenafil) has been successfully used as a treatment by many.

However, Cialis like Viagra, interacts with protease inhibitors. This can mean that the chance of experiencing side-effects and their severity is increased.



Amyl, butyl or isobutyl nitrite, are recreational drugs sniffed during sex to both intensify the experience and relax anal sphincter muscles.


A protein which speeds up a chemical reaction.

Both the erectile dysfunction drugs belong to the same class and are metabolised by the liver using the P450 enzyme, which is also employed by protease inhibitors. Men taking protease inhibitors are advised to reduce the standard 50mg dose of Viagra by 50% and a similar dose reduction should be made with Cialis which is normally available in 10 mg or 20mg pills. Taking higher doses of the drug can worsen the severity of side-effects, which can include headache, upset stomach, and facial swelling. More serious side-effects have been noted, especially in people with heart problems.

Demand for Cialis is expected to be high, particularly as studies suggest that a single dose allows men to obtain an erection at any point in the 24 hours after taking it, and because it is effective within ten to twenty minutes.

However, like Viagra, the medicine should not be used at same time with “poppers” (amyl nitrate) as this can cause a potentially fatal drop in blood pressure. It should also be used with caution by people with heart conditions and blood pressure problems.

Although fully licensed in Europe, the cost of Cialis means that NHS prescriptions will only be available to men with certain medical conditions. Hospital consultants can however prescribe to a wider population of men who may benefit from its use, and as with Viagra many men, some of whom have no erectile problems, are expected to buy the drug over the internet.

Further information on this website

Sexual dysfunction - Factsheet