The Food and Drug Administration (FDA) has approved a new antiretroviral drug with a unique mechanism of action for use in combination antiretroviral therapy. Maraviroc (Selzentry), the first CCR5 antagonist, is for use in patients with a particular strain of HIV, CCR5-tropic HIV-1 (also known as the R5 virus), who have a high viral load that treatment with other HIV medications has not reduced. HIV enters a T cell by attaching to a receptor on its surface. Maraviroc blocks CCR5-tropic HIV-1 from entering by binding to it at the CCR5 coreceptor, unlike the drugs in all the other classes of oral HIV medication, which fight the virus after it has already entered the cell. Because maraviroc is not effective against other strains of HIV, infection with CCR5-tropic HIV-1 must be confirmed before starting therapy.

The FDA granted maraviroc accelerated approval in light of 24-week data on 1,049 patients involved in two ongoing double-blind, controlled clinical trials of the drug. Those taking the drug in combination with other antiretrovirals showed significantly greater decreases in viral load; twice as many had undetectable viral loads at 24 weeks compared with those receiving other antiretrovirals without maraviroc. Maraviroc is taken orally twice daily. Its most common adverse effects are cough, fever, upper respiratory tract infection, rash, musculoskeletal symptoms, abdominal pain, and dizziness.

The product labeling for maraviroc notes that two serious adverse effects may occur. A "black box" warning indicates that there is a risk of hepatotoxicity, as determined by one case that occurred in a healthy volunteer and by an increased incidence of hepatic adverse effects among study subjects. The warning notes that hepatotoxicity may be preceded by signs of a systemic allergic reaction (such as an itchy rash, an increased eosinophil count, or an elevated immunoglobulin E level) and that if a patient has signs or symptoms of an allergic reaction or hepatitis, she or he should be evaluated immediately for hepatotoxicity. The other serious adverse effect, although not in the black box warning, is the risk of cardiovascular events, including myocardial ischemia or infarction, or both. Maraviroc should be used with caution in patients who have cardiovascular risk factors.

Nurses teaching patients to use maraviroc should be sure to emphasize that, despite decreasing the viral load, the drug does not lower the risk of giving HIV to another person through sexual contact, sharing hypodermic needles, or exchanging body fluids. Patients should be instructed to practice safer sex and to neither share nor reuse needles. Because it diminishes the effectiveness of the drug, patients should also be told not to take St. John's wort (Hypericum perforatum) or any product that contains it. Additionally, patients should be informed that their viral load might increase if they stop taking maraviroc for even a short time, so it is important to refill prescriptions before the supply runs out.