ICAAC: African-Americans less likely to experience immunologic failure when taking efavirenz

HIV-positive African-Americans are less likely to experience immunologic failure of a highly active antiretroviral therapy (HAART) regimen containing efavirenz (Sustiva) than Caucasians, according to research presented to the 44^th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in Washington. Research presented earlier this year at the Conference on Retroviruses and Opportunistic Infections (CROI), and reported on aidsmap.com found that African Americans may have a gene which results in slower clearance of efavirenz, implying greater drug exposure over time.

Investigators at the Atlanta Veterans Affairs Medical Center compared virologic and immunologic responses to HAART regimens containing either lopinavir / ritonavir (Kaletra) or efavirenz in 626 African-American and Caucasian individuals. To be included in the study patients needed to have been taking a HAART regimen including one of the study medications for at least a month. Patients were excluded if they were taking both Kaletra and efavirenz.

Patients were regarded as having experienced virologic failure if they had two consecutive viral load measurements above 400 copies/ml two months after starting HAART including Kaletra or efavirenz. Immunologic failure was defined as an increase in CD4 cell count of 50 cells/mm³ or less two months after starting HAART including Kaletra or efavirenz.

Multivariate analysis was performed to determine the relationship between race and immunologic and virologic failure controlling for age, HIV risk category, baseline and lowest-ever CD4 cell count, baseline viral load, previous experience of antiretroviral medication, history of AIDS defining illnesses, infection with hepatitis C virus, and number of years of known HIV infection.

The investigators found that amongst patients taking Kaletra or efavirenz, African American race was protective against immunologic failure (hazard ratio [HR] 0.64, 95% confidence interval [CI]: 0.45 – 0.91). Race was not found to protect against virologic failure (HR 0.85, 95% CI: 0.59 – 1.23).

The investigators then looked at the results for each particular drug and found that African Americans were less likely to experience immunologic failure on efavirenz (HR 0.62, 95% CI: 0.43 – 0.92), but there was no difference in the risk of virologic failure (HR 0.92, 95% CI: 0.62 – 1.38). Race was not protective against either immunologic or virologic failure of Kaletra, although there was a trend towards a lower risk of immunologic failure. Longer duration of treatment with efavirenz or Kaletra was also protective against immunologic failure.

“Race is associated with immunologic failure to efavirenz but not Kaletra,” conclude the investigators. They add that in a “population with equivalent access to medical care and antiretroviral agents, genetic factors may contribute to the differences in immunologic failure.”