THE TOXICITY OF AZIDOTHYMIDINE (AZT) ON HUMAN AND ANIMAL-CELLS IN CULTURE AT CONCENTRATIONS USED FOR ANTIVIRAL THERAPY

AZT, a chain terminator of DNA synthesis originally developed for chem otherapy, is now prescribed as an antihuman immunodeficiency virus (HI V) drug at 500 to 1500 mg/person/day, which corresponds to 20 to 60 mu M AZT. The human dosage is based on a study by the manufacturer of th e drug and their collaborators, which reported in 1986 that the inhibi tory dose for HIV replication was 0.05 to 0.5 M AZT and that for human T-cells was 2000 to 20,000 times higher, i.e. 1000 mu M AZT. This sug gested that HIV could be safely inhibited in humans at 20 to 60 mu M A ZT. However, after the licensing of AZT as an anti-HIV drug, several i ndependent studies reported 20- to 1000-fold lower inhibitory doses of AZT for human and animal cells than did the manufacturer's study, ran ging from 1 to 50 mu M. In accord with this, life threatening toxic ef fects were reported in humans treated with AZT at 20 to 60 mu M. There fore, we have re-examined the growth inhibitory doses of AZT for the h uman CEM T-cell line and several other human and animal cells. It was found that at 10 mu M and 25 mu M AZT, all cells are inhibited at leas t 50% after 6 to 12 days, and between 20 and 100% after 38 to 48 days. Unexpectedly, variants of all cell types emerged over time that were partially resistant to AZT. It is concluded that AZT, at the dosage pr escribed as an anti-HIV drug, is highly toxic to human cells.