Buprenorphine to Norbuprenorphine Ratio in Human Hair

Abstract

Recently, publications concerning buprenorphine and norbuprenorphine dosage in human hair appeared in the international literature (1,2). The authors reported that the parent-tometabolite ratio was generally lower than 1 in the hair specimens tested. For Vincent and colleagues (1), this ratio ranged from 0.34 to 0.66 in four hair samples and was 2.03 in only one case. For Wilkins et al. (2), buprenorphine concentrations ranged from 4.5 to 156.8 pg/mg and from 4.8 to 1438.5 pg/mg for norbuprenorphine in the hair of four subjects. Some years previously, Kintz et al. (3) and Tracqui coworkers (4,5) published data concerning buprenorphine and norbuprenorphine dosage in human hair revealing higher concentrations for the parent drug than for the metabolite. Kintz et al. (3) determined buprenorphine concentrations in the range 0.020 to 0.590 ng/mg in the hair of 14 young drug addicts admitted to a withdrawal program and norbuprenorphine concentrations ranged from not detected to 0.150 ng/mg in the same subjects. For Tracqui and co-workers (4), concentrations measured in the hair of six addicts undergoing substitutive therapy ranged from 0.004 to 0.140 ng/mg and from not detected to 0.067 ng/mg for buprenorphine and norbuprenorphine, respectively. It is generally admitted that the parent drug is present in hair in much higher concentrations than its corresponding metabolite(s). The hypothesis of a better incorporation of the metabolite in hair in contrast to the parent buprenorphine has been proposed (1). The aim of this paper was to investigated complementary experimentations in order to explain these contradictory observations.