Negative urine opioid screening caused by rifampin-mediated induction of oxycodone hepatic metabolism.
BACKGROUND
Oxycodone has become widely used in the clinic for the treatment of chronic pain. This reflects its favorable pharmacokinetics and side effect profiles.


METHODS
We report a 60-y-old man who had a clinically significant drug interaction between rifampin and oxycodone, resulting in 3 consecutive negative urine oxycodone screens in a 2-month period, suggesting non-adherence. A combination of urine opioid metabolite quantification by GC/MS and CYP genotyping confirmed that he was compliant with his oxycodone therapy. Determination of the complete oxycodone metabolite profile and the CYP3A4/5 and 2D6 genotype allowed the physician to be confident that the patient was compliant with the medication (and not diverting it) and to increase his oxycodone dose to optimize his pain control.


CONCLUSIONS
This case demonstrates how the combination of analytical toxicology and pharmacogenetic analyses enhances a physician's ability to personalize drug therapy in patients with chronic pain syndromes.
Lee
Hong-Kee
HK
Department of Pathology, Dartmouth Medical School and Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, United States.
Lewis
Lionel D
LD
Tsongalis
Gregory J
GJ
McMullin
Matthew
M
Schur
Bernard C
BC
Wong
Steven H
SH
Yeo
Kiang-Teck J
KT
D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D005838:Genotype; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015394:Molecular Structure; D009294:Narcotics / Q000737:chemistry / Q000652:urine; D010098:Oxycodone / Q000009:adverse effects / Q000737:chemistry / Q000493:pharmacokinetics*; D012293:Rifampin / Q000494:pharmacology*
D009294:Narcotics; D003577:Cytochrome P-450 Enzyme System; D010098:Oxycodone; C510164:CYP3A5 protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D012293:Rifampin