A mathematical model of CD4+ lymphocyte depletion in HIV infection is used to simulate and analyse the effect of AZT treatment. In most cases, permanent administration of AZT is observed to stop the CD4+ lymphocyte count decline and to stimulate their increase up to a new steady-state level, which depends on the intensity of AZT treatment, i.e. AZT dose. Temporary administration of AZT leads only to a temporary increase in CD4+ lymphocyte count. After the treatment is terminated, the count starts to decline again. However, the resulting prolongation of patient's survival exceeds the time interval of AZT administration. Interestingly, the survival prolongation is greater, if the treatment is started at five than at two years after the infection and there is no striking increase in survival time if a dose of AZT inhibiting 75% of HIV proliferation is used instead of a lower one inducing 25% inhibition only.

CD4 Lymphocyte Count/*DRUG EFFECTS Human HIV/DRUG EFFECTS/PHYSIOLOGY HIV Infections/*DRUG THERAPY/IMMUNOLOGY/MORTALITY *Models, Biological Survival Analysis Virus Replication/DRUG EFFECTS Zidovudine/ADMINISTRATION & DOSAGE/*PHARMACOLOGY/THERAPEUTIC USE JOURNAL ARTICLE

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