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.

View Table: Mechanisms of Drug Interactions

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.

View the Inhibitors and Inducers of CYP Enzymes, P-Glycoprotein, and Other Transporters tables

The ability of grapefruit juice to increase serum concentrations of drugs was first discovered during a study of the effect of ethanol on felodipine (Plendil) pharmacokinetics. Double-strength grapefruit juice used to disguise the taste of ethanol resulted in higher than expected serum concentrations of felodipine (DG Bailey et al, Clin Invest Med 1989; 12:357).

Antiretroviral therapy is recommended for all HIV-infected patients, both to reduce the risk of disease progression and to prevent transmission of the virus to others. Various guidelines for treatment of HIV infection are available.

Implanon (Organon), an implantable contraceptive containing the progestin etonogestrel, has been approved by the FDA. Two other implantable contraceptives, Norplant and Jadelle, which both contain levonorgestrel, are FDA-approved but not marketed in the US.

The centuries-old anti-inflammatory drug colchicine (Colcrys, and others) is FDA-approved for prophylaxis and treatment of gout flares and for treatment of familial Mediterranean fever. It is also used off-label to treat pericarditis, and in recent years has been investigated for reduction of cardiovascular risk in patients with coronary artery disease (CAD).

Darunavir (Prezista - Tibotec), a new protease inhibitor, has received accelerated approval from the FDA for use in combination therapy of human-immunodeficiency virus (HIV) infection in previously treated adults. It is coadministered with low-dose ritonavir (Norvir), which increases its bioavailability.