Disposition of propoxyphene and norpropoxyphene in man after a single oral dose.

Abstract

The disposition of propoxyphene and its major biotransformation product norpropoxyphene was studied in normal subjects following a single 130 mg oral dose. The concentration of propoxyphene and norpropoxyphene in samples of plasma and urine was determined by use of gas‐liquid chromatography. The peak plasma level of propoxyphene occurs at 2 hours followed by a rapid elimination with an average apparent half‐life of 3.0 hours (range 1.6 to 4.1 hours). The plasma level of norpropoxyphene renches a peak at 4 hours and slowly decays with an apporent half‐life of 16.8 hours (range 11.5 to 28.8 hours). For a given subject, the ratio of the concentration of propoxyphene over the norpropoxyphene in plasma at 4 hours after a 130 mg dose is well correlated with the apparent plasma half‐life of propoxyphene. This suggests that this single plasma sample may provide an indication of the rewtive rate of N‐demethylation in a population. The data indicate that individual ditJerences in absorption and biotransformation may be responsible for the substantial variation of the pklsma propoxyphene levels seen in subjects receiving the same dose.