Objectives: To investigate the factors related to viral load becoming undetectable among patients from Southern Alberta who started a protease inhibitor for the first time, and to determine the factors related to subsequent re-emergence of detectable viral load amongst those patients whose viral load initially became undetectable.
Subjects and methods: A total of 243 patients from the Southern Alberta Clinic had started a protease inhibitor for the first time and had been followed up for a median time of 32 weeks. Standard survival techniques including Kaplan-Meier techniques and Cox proportional hazards models were used to determine which factors were related to viral load becoming undetectable.
Results: At 24 weeks after first exposure to a protease inhibitor, 52.8% of the patients [95% confidence interval (Cl), 45.2-56.6] had achieved an undetectable viral load. In a multivariate analysis, those with a higher initial viral load were less likely to become undetectable [relative hazard (RH), 0.50; 95% Cl, 0.35-0.70; P < 0.0001], whereas those starting more new drugs (RH per new drug, 1.54; 95% Cl, 1.01-2.11; P = 0.048) were significantly more likely to achieve an undetectable viral load. Amongst 111 patients whose viral load became undetectable, Kaplan-Meier analysis indicated that 15.5% of patients experienced re-emergence of detectable viral load at 24 weeks after the first undetectable viral load. A higher CD4 cell count was associated with a lower risk of viral load becoming detectable (RH, 0.73; 95% Cl, 0.53-1.00; P = 0.049), as was treatment with indinavir (versus any other protease inhibitor RH, 0.17; 95% Cl, 0.03-0.86; P = 0.033).
Conclusions: A significant proportion of patients in a routine clinic setting achieved an undetectable viral load measurement after first starting a protease inhibitor; viral load in patients with a higher CD4 cell count was more likely to become and stay undetectable. There was no evidence that patients who were drug-naive experienced significantly worse virological effects than drug-experienced patients, as long as the same number of new drugs was started at the date of first exposure to a protease inhibitor. Further follow-up of these patients is warranted to study the longer term effects of treatment with protease inhibitors.