Hydroxyurea and didanosine is a more potent combination than hydroxyurea and zidovudine.

The in vitro and in vivo antiviral activity of hydroxyurea in combination with either zidovudine or didanosine was evaluated in primary human peripheral mononuclear cells and in a cohort of 29 asymptomatic patients infected with HIV. In vitro, hydroxyurea alone did not significantly affect HIV replication, whereas the combination of hydroxyurea with didanosine was more effective than the combination of hydroxyurea with zidovudine. Our clinical results confirmed these studies. Patients were randomly assigned to five arms (zidovudine, hydroxyurea or didanosine monotherapy, or hydroxyurea in combination with either zidovudine or didanosine) to evaluate preliminary safety and efficacy. Bone-marrow toxicity occurred in two patients treated with zidovudine plus hydroxyurea, alopecia was reported in one patient treated with hydroxyurea monotherapy, and there were no toxic effects recorded in the remaining three groups. Plasma viraemia was not influenced by hydroxyurea monotherapy, and the hydroxyurea-zidovudine combination did not give any advantage over either zidovudine or didanosine monotherapy (0.3-0.5 log decrease in plasma viraemia). In contrast, a 1.1 log drop in plasma viraemia was observed in patients treated with hydroxyurea plus didanosine, this reduction was sustained throughout the 24-week course of the treatment. Combination therapy with hydroxyurea and didanosine exhibited statistically significant improvements compared with the other therapeutic approaches. Although further clinical trials are required, these results suggest that hydroxyurea in combination with didanosine might be an effective and well-tolerated, simple and affordable, treatment for HIV infection.