The concentration of propoxyphene in the plasma and analgesia scores in postpartum patients

Equimolar quantities of 2 propoxyphene salts were administered as single oral doses to women reporting postpartum uterine cramping. The doses included 32, 65, and 130 mg of the hydrochloride and 50, 100, and 200 mg of the napsylate salt. Identical-appearing placebo capsules were included. Both analgesia scores and plasma concentrations were determined. The correlation between these 2 measures of response was not significant when all of the 336 pairs of individual observations were included in the computation. Both responses were related to amount of drug ingested, and on this basis the means of the analgesia scores and the concentrations in the plasma were significantly correlated.