HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PHENOTYPES IN CHILDREN WITH ADVANCED DISEASE TREATED WITH LONG-TERM ZALCITABINE

Baseline and posttreatment human immunodeficiency virus type 1 (HIV-1) isolates from 38 symptomatic, zidovudine-experienced HIV-1-infected c hildren enrolled in a prospective trial of zalcitabine (dideoxycytidin e) monotherapy (Pediatric AIDS Clinical Trials Group 138) were studied for the presence of syncytium-inducing (ST) phenotype and zalcitabine resistance. Twenty of the isolates were SI and 18 were non-SI (NSI) a t baseline. After >44 weeks of zalcitabine treatment, the SI and NSI p henotypes were maintained in 16 and 17 patients, respectively. One pat ient had an NSI-to-SI phenotypic switch, while SI-to-NSI reversion occ urred in 4 children (20%). Isolates from 30 of these patients were ana lyzed by in vitro drug susceptibility assay: Mean IC50 values were 0.1 4 mu M at baseline and 0.18 mu M following zalcitabine treatment. Only 1 child (3%) developed zalcitabine resistance. Knowledge of the low i ncidence of zalcitabine resistance and the switch from SI to NSI pheno type in some children may prove useful when selecting antiretroviral d rugs to be used in combination.