Urine
drug monitoring is used by physicians treating
chronic pain patients with
opioid therapy. Patients are tested in part to insure that they are not taking other drugs. Therefore, the finding of
codeine in a patient who is only prescribed
morphine has clinical implications.
Morphine preparations are known to have small amounts of
codeine as an impurity estimated to be about 0.04%. In a population of 535
pain patients prescribed
morphine, Kadian,
MS Contin, and/or Avinza, the investigators observed 24 samples that contained
codeine >20 ng/mL. Fifteen of the 24 contained
codeine >20 and <50 ng/mL. Of the 9 samples that were >50 ng/
mL, 7 had high levels of
codeine (indicating
codeine use), 1 was from a patient who had a prescription for
codeine, and 1 was also positive for
6-acetylmorphine, indicating
heroin use. A control group of 680 patients taking
oxycodone was negative for
codeine. The finding of
codeine was ascribed to the manufacturing process of the
morphine medications. Clinicians and laboratories testing urine for drugs should be aware of this possibility.