The Food and Drug Administration (FDA) last week announced the addition of updated drug interaction information to the prescribing information of all currently approved HIV protease inhibitors.

Protease inhibitors are a class of antiretroviral drugs that prevent HIV from replicating by blocking a necessary protein called protease.

Drugs in this class include Aptivus (tipranavir), Crixivan (indinavir), Invirase (saquinavir mesylate), Kaletra (lopinavir/ritonavir), Lexiva (fosamprenavir), Norvir (ritonavir), Prezista (darunavir), Reyataz (atazanavir), and Viracept (nelfinavir).

Although some of the drug interactions had been known for specific protease inhibitors, the added information will affect all currently approved drugs in this class.

Drugs that should be avoided by individuals taking protease inhibitors include:

• Revatio (sildenafil), used to treat pulmonary arterial hypertension, a condition in which blood pressure in the arteries of the lungs is abnormally high. Protease inhibitors tend to increase concentrations of Revatio in the bloodstream, which could cause a dangerously low drop in blood pressure.
• Uroxatral (alfuzosin), which is used to treat men who have an enlarged prostate. Protease inhibitors increase the risk of severe low blood pressure in men taking Uroxatral.

The active ingredient in Revatio, sildenafil, is also the active ingredient in Viagra. Pfizer, which makes Viagra, recommends that men taking protease inhibitors should take no more than 25 mg of Viagra in a 48-hour period.

The FDA also listed several drugs that should not be given at the same time as protease inhibitors, including:

• Salmeterol (Serevent), which is used in asthma treatment. Protease inhibitors can lead to an increased risk of heart problems when given with salmeterol.
• Tracleer (bosentan), another drug for treatment of pulmonary arterial hypertension. Tracleer should not be given with Reyataz unless Norvir is also prescribed. Cotreatment with Tracleer and Reyataz without Norvir may result in higher blood concentrations of Tracleer, increasing both its activity and side effects.
• Colchicine, a natural product often used to treat gout, and which should not be given at the same time as protease inhibitors in patients with liver or kidney problems. Protease inhibitors may slow the rate at which the intestine and liver process colchicine.

Finally, several drugs were found to need dosing adjustments if administered with protease inhibitors. These include:

• Adcirca (tadalafil), another treatment for pulmonary arterial hypertension. Protease inhibitors can affect the amount of Adcirca in the body, so dosages should be monitored carefully.
• Colchicine for all patients taking protease inhibitors, when prescribed for the treatment of familial Mediterranean fever and gout or gout prevention.

Patients taking protease inhibitors should speak to their physicians before beginning or ending any drug regimens, and should tell doctors about all medications they are taking.

For more information on protease inhibitor drug-drug interactions, please see the FDA website.