Genotypic and phenotypic resistance were analysed in the virology subset of 173 Delta 1 AZT-naive patients at baseline, 24, 48, 80 and 112 weeks after commencing therapy (AZT alone, AZT plus ddI or AZT plus ddC). Using the point mutation assay (PMA) genotypic changes were investigated at codons 41, 67, 70, 215, 219 (AZT), 65, 69,74,75 and 184 (ddC/ddI). Proportion values above, 4% for T215F/Y and 2% for all other mutant codons were regarded as resistant. Pre-treatment analysis demonstrated that 10 of 173 patients (pt) had detectable genotypic resistance (T215F/Y = 2pt; K70R = 7pt; T215F/Y + K70R = lpt) to date 3 out of 10 have been found not to exhibit phenotypic resistance. No mutations were identified at any other points prior to therapy. The proportion of patients with AZT resistance at codon 70 was significantly greater in the, AZT-alone group than in the combination therapy groups(logrank p less than 0.0001). No significant differencs in the proportion of the other resistant mutations associated with AZT were found between the treatment groups. In patients receiving combination therapies no mutations associated with ddI or ddC were detected out to 112 weeks. Further analysis of data including quantitative measures of genotypic resistance and phenotypic resistance will be presented.

Antiviral Agents/ADMINISTRATION & DOSAGE/*THERAPEUTIC USE Clinical Trials Codon Didanosine/ADMINISTRATION & DOSAGE/THERAPEUTIC USE Drug Resistance, Microbial/*GENETICS Drug Therapy, Combination *Genotype HIV Infections/DRUG THERAPY/*VIROLOGY HIV-1/*GENETICS Human *Phenotype Point Mutation Zalcitabine/ADMINISTRATION & DOSAGE/THERAPEUTIC USE Zidovudine/ADMINISTRATION & DOSAGE/THERAPEUTIC USE ABSTRACT

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