Dr. Frank and colleagues presented 24 week results of a phase I/II, randomized, placebo-controlled five-arm study comparing HU alone at two doses (1000 mg a day and 1500 a day), ddI alone (200 mg twice a day), and ddI/HU in treatment naïve and experienced subjects. The HU groups had ddI added after week 4; the ddI group had HU (1000 mg or 1500 mg) added after week 12. The study enrolled 134 patients, 45% of whom had had no previous antiretroviral experience.

The following table shows the mean changes in viral load (in log copies/ml), followed by the percentage of patients with viral loads below 400 copies/mL on each arm. No statistically significant differences in activity were seen comparing the low and high dose HU + ddI arms (which were therefore combined in the table below) or the treatment-naïve versus treatment-experienced subjects:

Neutropenia, or low white blood cell counts, were more likely in the higher dose HU arm.

The study authors concluded that HU alone had no antiretroviral activity, but was synergistic with ddI. However, patients already on ddI had no change in viral load after adding HU at Week 12, so the authors recommend starting both treatments together.