Interpreting urine drug tests: prevalence of morphine metabolism to hydromorphone in chronic pain patients treated with morphine.
OBJECTIVE
Pain medicine practitioners frequently use urine drug testing (UDT) to monitor adherence to opioid therapy. It can be difficult to interpret a result as normal or abnormal in relation to which opioid compounds are expected to be found in the urine. We investigated whether hydromorphone may be a metabolite of morphine normally appearing in UDT of patients prescribed morphine.


METHODS
This is a retrospective case-control study of urine toxicology results in pain patients taking only morphine. Inclusion criteria included urine results positive for morphine only (controls) or morphine and hydromorphone (cases). Demographic and medical history variables, and any history of aberrant drug behavior were recorded and related to the presence or absence of hydromorphone in the urine.


RESULTS
Hydromorphone was present in 21 of 32 cases (66%), none of whom had a history of aberrant drug behavior. Positive cases occurred more frequently in women, in those taking higher daily doses of morphine, and in those with higher urine morphine concentrations (P < 0.05). Only morphine urine concentration was a significant predictor of the hydromorphone metabolite in a logistic regression model (P < 0.05).


CONCLUSIONS
Hydromorphone is likely a minor metabolite of morphine, normally appearing in the UDT of patients taking morphine. This finding assists in determining whether a UDT result is normal or abnormal, and subsequently whether a patient is compliant with opioid therapy. This observation should be confirmed by a prospective study in a controlled environment. Variables such as gender, morphine dose, morphine urine concentration, and genetic determinants of morphine metabolism should be investigated further.
Wasan
Ajay D
AD
Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA. awasan@partners.org
Michna
Edward
E
Janfaza
David
D
Greenfield
Shelly
S
Teter
Christian J
CJ
Jamison
Robert N
RN
D002908:Chronic Disease; D005260:Female; D006801:Humans; D004091:Hydromorphone / Q000652:urine*; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000627:therapeutic use* / Q000652:urine*; D010146:Pain / Q000188:drug therapy* / Q000652:urine*; D015995:Prevalence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D015813:Substance Abuse Detection / Q000379:methods*; D016482:Urinalysis / Q000379:methods*
D009020:Morphine; D004091:Hydromorphone