Rifapentine, a long-acting analog of rifampin developed in the 1960's, has received an accelerated approval from the FDA for oral use, with at least one other drug, in the treatment of pulmonary tuberculosis.

Lopinavir/ritonavir is the first fixed-dose combination of protease inhibitors approved by the FDA for the treatment of HIV infection. It is being marketed for use with other drugs in adults and children more than six months old. Lopinavir is a new drug available only in this combination. Ritonavir is often used with other protease inhibitors to raise their plasma concentrations.

Vardenafil (Levitra -Bayer) is the second oral drug approved by the FDA for treatment of erectile dysfunction. Sildenafil (Viagra - Medical Letter 1998; 40:51), the first oral drug, has been available for 5 years. Pharmacokinetics, effectiveness, adverse effects, dosage and cost of the new drug are reviewed. Whether it offers any benefits over sildenafil is discussed.

Serious adverse interactions between drugs continue to be reported. Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

Four new drugs have become available in the USA for HIV infection or its complications. Nevirapine (Viramune - Roxane), intravenous cidofovir (Vistide - Gilead), and amphotericin B oral suspension (Fungizone Oral Suspension - Bristol-Myers Squibb) have been approved by the US Food and Drug Administration; nelfinavir (Viracept - Agouron) is currently available only through an "Expanded Access Program."

Combination antiretroviral therapy including protease inhibitors has dramatically changed the treatment of HIV infection and the prognosis of those affected (Medical Letter Handbook of Antimicrobial Therapy, 1998, page 122). Due to limitations and failures with these drugs in many patients, however, three new drugs, none of them protease inhibitors, have rapidly come into wide use in clinical trials or 'expanded access' programs. They are abacavir (Ziagen - Glaxo Wellcome), adefovir (Preveon - Gilead) and efavirenz (Sustiva - DuPont). Efavirenz was recently approved for treatment of...

Amprenavir is the fifth protease inhibitor to become available for treatment of HIV infection. It was approved by the FDA for use with other drugs in the treatment of HIV-infected adults and children at least four years old.

Tipranavir (Aptivus - Boehringer Ingelheim), a new protease inhibitor, has received accelerated approval from the FDA. It must be given with ritonavir (Norvir). The combination is indicated for use with other antiretrovirals to treat HIV infection in highly treatment-experienced adults who have ongoing viral replication or in those with HIV strains known to be resistant to multiple protease inhibitors.

A recent letter to the editor of the Annals of Internal Medicine documented a single case of myopathy apparently due to an interaction between simvastatin (Zocor, and others) and green tea. Since it became available generically, simvastatin has surpassed atorvastatin (Lipitor) as the best selling statin. As such, it is probably the most common cause of statin-induced myopathy, which is often a result of drug interactions.

Changes caused by one drug in the absorption, distribution, metabolism or excretion of another may lead to a pharmacokinetic adverse drug interaction (DN Juurlink et al, JAMA 2003; 289:1652). Additive drug interactions, such as vasodilation caused by both sildenafil (Viagra) and nitrates, can also have adverse effects.