ch02.qxd 102 8/13/2001 1:15 PM Page 102 A NTIMICROBIAL D RUGS DIDANOSINE Videx, Videx EC Pharmacology Didanosine (dideoxyinosine [ddI]) is a purine nucleoside that undergoes complex metabolism in vivo to dideoxyadenosine (ddA), which ultimately undergoes metabolism to an active triphosphorylated form (ddATP) Incorporation of ddATP into viral DNA leads to chain termination, and ddATP is a competitive inhibitor of HIV reverse transcriptase, which further contributes to the interference of HIV replication.95,96 Administration and Adult Dosage PO for HIV infection (tablets or solution) (≥60 kg) 200 mg (as tablets) q 12 hr, or 400 mg/day (as tablets), or 250 mg (as powder) q 12 hr; (