Problems and solutions to single-dose testing of analgesics: comparison of propoxyphene, codeine, and fenoprofen.

Discrepancies exist between reports arising from single-dose and multiple-dose studies intended to compare the efficacy of oral analgesics. D Differences in the pharmacokinetic characteristics of these drugs account for much of the discord. Codeine and fenoprofen rapidly achieve their ultimate plasma equilibrium levels (on a q. 6h. schedule), whereas, propoxyphene requires a longer period, doubtless due to its longer half-life and proportionately smaller maintenance dose. If the drugs are not to be compared during the steady state, then administration of appropriate loading doses permits satisfactory single dose comparisons at steady-state concentrations.