AIDS Treatment Update, Issue 59, November 1997
Edward King

Before they can exert anti-HIV effects, both AZT and d4T have to be converted into their active form by cellular enzymes, in a process called phosphorylation. In the Altiphar study, researchers found that the phosphorylation of d4T was less effective in AZT-experienced people compared with AZT-naive people, resulting in lower levels of the active form of d4T in the AZT-experienced people.

This might suggest that to get the most from these drugs, d4T-based regimens should be used prior to AZT-based regimens. However, the study did not examine the opposite question: whether the activity of AZT is hampered in d4T-experienced people. Also, no-one yet knows whether other NRTI drugs are affected in similar ways.

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