Study details Although people living with HIV/AIDS using AZT are usually prescribed 500 or 600 mg/day, anecdoctal reports suggest that people may be taking 300 or 400 mg/day. This dose reduction may reduce side effects and the cost of the drug. Doctors in Mexico city conducted a small study to find out the effect of different doses of AZT on the development of drug-resistant virus. Doctors recruited 15 HIV-infected subjects who had between 200 and 500 CD4+ cells. Subjects were assigned to the following groups: * AZT 500 mg/day * AZT 300 mg/day * no AZT (or any other anti-HIV drugs) Blood samples were taken from the subjects for analysis before they entered the study and at regular intervals.

Results During the course of the study, technicians isolated HIV from blood samples and exposed the virus to AZT in lab experiments. They found at the end of the study, HIV from subjects who used the high dose of AZT required huge quantities (750 times the normal amount) of the drug to suppress production of HIV in the test tube. Virus taken from subjects using AZT 300 mg/day needed less drug (93 times the normal level) to block its activity. Subjects not receiving AZT had HIV that required even less drug to suppress its production. The difference between the concentrations of AZT required to suppress the virus before and after entering the study was [statistically] significant.

Interpretation Although researchers are not sure which dose of AZT is best, 300 mg/day in combination with other anti-HIV agents may be a reasonable dose to use. The study could have been a more useful piece of research had the doctors also measured changes in viral load.

REFERENCES: 1. Soto-Ramirez L, Renjifo B, Marlink R, et al . Dose-dependent HIV-1 Zidovudine resistance. Abstract I111.

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