A rapid method for measuring pyridinone HIV-1 reverse transcriptase inhibitor plasma levels was necessary for identifying potential clinical candidates and for choosing a clinical formulation. Due to its sensitivity to the pyridinones, ability to tolerate extraneous material, and its capability for rapid, high through-put screening, the HIV-1 RT assay was developed into a bioassay for determining plasma levels of the pyridinones in Rhesus monkey plasma. With this assay, dose proportionality of L-697, 639 was established. Formulation studies using L-697, 639 indicated that the plasma levels achieved in Rhesus monkeys with the clinical formulation (peak levels = 3.9 microM at 30 min) fall between the levels achieved with polyethylene glycol 300 and hydroxypropyl methyl cellulose formulations (peak levels = 8.9 microM and 0.4 microM respectively, at 60 min). Two other pyridinones, L-696, 229 and L-697, 661, administered as the clinical formulation, had peak plasma levels of 1.6 microM (30 min) and 0.3 microM (60 min), respectively. In Rhesus monkeys, the bioavailabilities of these compounds (administered as the clinical formulation) ranged from 11 to 24% and their half-life values ranged from 24 to 120 min. The results of oral studies in Rhesus monkeys with these compounds were very similar to initial results of studies in humans.