September 8, 2006

Standard Dosage Works for Overweight

Size doesn’t matter. This is the conclusion of a new study exploring whether people with high body mass indexes (BMI) – those who are overweight or obese – are less likely to respond favorably to HIV treatment. The data, published in the September issue of the Journal of Acquired Immune Deficiency Syndromes, refutes the hypothesis that larger-than-average HIV-positive people may need to be treated with higher doses of HIV medications to achieve durable viral load suppression and stable CD4 cell counts.

Studies have demonstrated that BMI can influence the way drugs are metabolized and distributed in the body. For example, a possible reason why women may be more likely to experience certain side effects – or have more severe side effect symptoms – is because their average body weights are lower than the average body weights of the males that make up the vast majority of dose-determining clinical trials. In other words, some women may be taking higher doses of a drug than they need, based on their lower body weight.

On the other end of the spectrum are people who are overweight or obese. The U.S. Centers for Disease Control’s HIV Outpatient Study (HOPS) conducted a study to evaluate whether overweight or obese HIV-positive people – who, like people of lower-than-average body weight may not be adequately represented in clinical trials – are more likely to experience treatment failure, due to the possibility of too little medication in their bodies.

Using data collected in HOPS, an ongoing cohort involving thousands of HIV-positive people, Ellen Tedaldi, MD, and her colleagues analyzed the association of BMI with achieving an undetectable viral load and experiencing a CD4 count increase of more than 100 cells after three to nine month of HIV treatment.

Among 711 patients included in analysis, 43% had a BMI of more than 25, which is considered to be overweight or obese.* Higher BMI was associated with being female, being black or Hispanic, being heterosexual, and using injection drugs. Although average pre-treatment viral loads were significantly lower in obese participants, overweight or obese BMI did not significantly alter the likelihood of achieving an undetectable viral load and a CD4 cell count increase of more than 100 cells compared with lower-weight study participants.

In conclusion, Dr. Tedali’s group indicated that a substantial proportion of the patients included in the HOPS analysis were overweight or obese. However, increased BMI was not associated with decreased virologic or immunologic responses to HIV treatment. This, they suggest, argues against the likelihood of requiring higher-dose treatment to manage HIV in larger-than-average patients.

Other studies, exploring the possibility of using lower-dose therapy in HIV-positive people with below-average body weights to potentially reduce the risk of side effects, have not yet been conducted.

* To calculate your BMI, first multiply your height in inches by your height in inches (e.g., 74” X 74” = 5,476). Next divide that number into your body weight (e.g., 200 / 5476 = 0.0365). Finally multiple that number by 703 (0.0365 X 703 = 25.66). This final number is your BMI. The National Heart, Lung, and Blood Institute has an automated calculator that can be used to calculate your BMI.

While BMI is considered to be a reliable indicator of total body fat, it does have some limits. It may overestimate body fat in people who have muscular builds and may underestimate body fat in some people, including people with AIDS-related wasting, who have lost muscle mass.