Giacomini K M, Gibson T P, Levy G
J Clin Pharmacol. 1978 Feb-Mar;18(2-3):106-9. doi: 10.1002/j.1552-4604.1978.tb02429.x.
The free fraction of d-propoxyphene in the plasma of normal subjects is 0.24 +/- 0.02 (mean +/- S.D.) and is not concentration dependent in the usual therapeutic and toxic conentration range. Renal failure and relatively high concentrations of d-norpropoxyphene, the major metabolite of d-propoxyphene, have no significant effect on the plasma protein binding of d-propoxyphene.
