In HIV-infected subjects who have received little or no prior antiretroviral therapy, treatment with abacavir alone or in combination with ZDV is well tolerated and resulted in sustained improvements in key immunologic and virologic efficacy parameters through 12 weeks.

A hydroxynaphthoquinone compound (566C80) has been shown to be effective in the prevention and treatment of murine Pneumocystis carinii pneumonitis. In a phase I study, five cohorts of four human immunodeficiency virus-infected men received 100, 250, 750, 1500, and 3000 mg of the compound orally once daily for 12 days. A sixth cohort received 750 mg three times daily for 5 days, then twice daily for 16 days. Evaluation included clinical, hematologic, and biochemical studies and the pharmacokinetics of 566C80. The only drug-related adverse effect was a maculopapular rash in one patient that resolved without discontinuation of the drug. With the largest dosage tested (3000 mg) the following pharmacokinetic measures were achieved: maximum plasma concentration, 39 micrograms/ml; time to maximum plasma concentration, 8.0 h; area under plasma concentration-time curve at steady state, 1088 h.micrograms/ml; plasma half-life, 51 h; and total plasma clearance, 4.09 l/h. Compound 566C80 offers promise as a new drug class for P. carinii pneumonia.

A new sensitive method for the measurement of lamivudine triphosphate (3TC-TP), the active intracellular metabolite of lamivudine in human cells in vivo, has been established. The procedure involves rapid separation of 3TC-TP by using Sep-Pak cartridges, dephosphorylation to 3TC by using acid phosphatase, and measurement by radioimmunoassay using a newly developed anti-3TC serum. The radioimmunoassay had errors of less than 21% and a cross-reactivity of less than 0.016% with a wide variety of other nucleoside analogs. The limit of quantitation of the assay for intracellular 3TC-TP was 0.195 ng/ml (0.212 pmol/106 cells), and a cell sample of only 4 million cells was ample for the assay. This procedure, combined with our previously developed method for measuring zidovudine (ZDV) metabolite levels, proved capable of measuring 3TC-TP, ZDV monophosphate (ZDV-MP) and ZDV triphosphate (ZDV-TP) in human immunodeficiency virus (HIV)-infected subjects treated with combination 3TC and ZDV therapy. In seven subjects, intracellular 3TC-TP levels ranged from 2.21 to 7.29 pmol/106 cells, while intracellular ZDV-MP and ZDV-TP levels ranged from <0.01 to 1.76 and 0.01 to 0.07 pmol/106 cells, respectively. Concentrations of 3TC in plasma determined in these subjects ranged from 0.34 to 9.40 μM, which was about fivefold higher than ZDV levels in plasma of 0.04 to 1.4 μM. This is the first study to determine the intracellular levels of the active metabolites in HIV-infected subjects treated with this combination. These methods should prove very useful for in vivo pharmacodynamic studies of combination therapy.