Dihydrocodeine: a new opioid substrate for the polymorphic CYP2D6 in humans.
BACKGROUND
The opioid dihydrocodeine (DHC) is frequently used as an analgesic and antitussive agent. However, until now there have been no detailed data on dihydrocodeine metabolism in humans. We therefore investigated pathways that contribute to elimination of dihydrocodeine, and we tested the hypothesis that dihydrocodeine O-demethylation to dihydromorphine (DHM) is catalyzed by the polymorphic CYP2D6.


METHODS
A single oral dose of dihydrocodeine was administered to six extensive (metabolic ratio [MR] < or = 1), two intermediate (1 < MR < 20) and six poor metabolizers (MR > or = 20) of sparteine/debrisoquin. Serum concentrations of dihydrocodeine and dihydromorphine were measured up to 25 hours, and urinary excretion of conjugated and unconjugated dihydrocodeine, dihydromorphine, and nordihydrocodeine were determined.


RESULTS
There were no differences in the pharmacokinetics of dihydrocodeine between extensive and poor metabolizers. However, the area under the serum concentration-time curve (AUC), partial metabolic clearance, and total urinary recovery of dihydromorphine were significantly lower in poor metabolizers (10.3 +/- 6.1 nmol.hr/L; 7.0 +/- 4.1 ml/min; 1.3% +/- 0.9% of dose) compared with extensive metabolizers (75.5 +/- 42.9 nmol.hr/L; 49.7 +/- 29.9 ml/min; 8.9% +/- 6.2%; p < 0.01). There was a strong correlation between the AUCDHC/AUCDHM ratio and the urinary metabolic ratio of sparteine (rS = 0.89, p = 0.001). No significant differences between extensive and poor metabolizers were detected in urine for conjugated dihydrocodeine (extensive metabolizers, 27.7% of dose; poor metabolizers, 31.5%), unconjugated dihydrocodeine (extensive metabolizers, 31.1%; poor metabolizers, 31.1%), conjugated nordihydrocodeine (extensive metabolizers, 6.3%; poor metabolizers, 5.4%), or unconjugated nordihydrocodeine (extensive metabolizers, 15.8%; poor metabolizers, 19.5%).


CONCLUSIONS
Dihydrocodeine O-demethylation to dihydromorphine is impaired in poor metabolizers of sparteine. The main urinary metabolites after administration of dihydrocodeine are the parent compound and its conjugates in extensive and poor metabolizers.
Fromm
M F
MF
Margarete Fischer-Bosch-Institut für Klinische Pharmakologie, Stuttgart, Germany.
Hofmann
U
U
Griese
E U
EU
Mikus
G
G
D000328:Adult; D003061:Codeine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D019389:Cytochrome P-450 CYP2D6; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004090:Dihydromorphine / Q000378:metabolism*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D006899:Mixed Function Oxygenases / Q000235:genetics*; D010641:Phenotype; D013034:Sparteine / Q000378:metabolism
D013034:Sparteine; D003577:Cytochrome P-450 Enzyme System; D004090:Dihydromorphine; D006899:Mixed Function Oxygenases; D019389:Cytochrome P-450 CYP2D6; C014481:dihydrocodeine; D003061:Codeine