The role of observational studies in assessing the impact of antiviral therapies

Rate of viral rebound according to specific drugs in the regimen in 2120 patients with HIV suppression

BACKGROUND

It is currently unclear whether the tendency for viral rebound in patients with viral load < 50 copies/ml differs according to the specific drug regimen being used.

METHODS

To follow 2120 patients in EuroSIDA who had attained < 50 copies/ml on highly active antiretroviral therapy (HAART), without previously virologically failing HAART.

RESULTS

The rate of viral rebound (two consecutive values > 400 copies/ml) was 4.9/100 person-years [95% confidence interval (CI), 4.0-5.8] for patients who were naive pre-HAART and 8.0/100 person-years (95% CI, 7.0-9.0) for those who were experienced with nucleoside analogue reverse transcriptase inhibitors (NRTI) pre-HAART. The rate of rebound was significantly higher in those taking nelfinavir than in those taking efavirenz, both in patients who were naive pre-HAART and those who were NRTI experienced [adjusted rate ratios, 2.83 (95% CI, 1.51-5.31) and 2.86 (95% CI, 1.65-5.00), respectively]. Among patients who were naive pre-HAART, those on abacavir had no evidence of a raised risk of viral rebound (adjusted rate ratio 1.17; 95% CI, 0.51-2.69), but in those with pre-HAART NRTI experience the rate was markedly raised (adjusted rate ratio, 4.48; 95% CI, 2.51-8.00). A similar picture was seen when comparing those on nevirapine with those on efavirenz, although the elevated rate ratio in pre-HAART experienced patients was of lower magnitude (adjusted rate ratio, 1.93). There was no strong evidence that rebound rates differed significantly for any NRTI pairs compared with zidovudine/lamivudine.

CONCLUSION

Viral rebound rates in patients who have attained < 50 copies/ml appear to differ according to the specific drugs being used.

The Problems Faced When Assessing the Prevalence and Incidence of Antiretroviral-Related Toxicities

Although the dramatic effect of highly active antiretroviral therapy (HAART) in reducing morbidity and mortality must not be underestimated, it is also important to consider the incidence and prevalence of HAART-related toxicities. Although several studies have investigated HAART-related toxicities, there has been great variety between them in the reported incidence and prevalence rates of these toxicities. Various factors, including whether the study type was a clinical trial or an observational study, the definition of the toxicity endpoints, the demographic characteristics of the study populations and the effect of calendar year on analyses, may all influence the rates observed. We investigated the possible explanations for the differences in the incidence and prevalence rates of HAART-related toxicities between studies, focussing on metabolic and hepatotoxic disorders.