Patients on methadone maintenance often have chronic pain, and those with more intense pain receive higher doses of methadone, said Einat Peles, Ph.D., and colleagues at Tel-Aviv Elias Sourasky Medical Center.
The researchers nonselectively enrolled 170 consecutive drug-abuse patients and found that 94 (55%) had experienced chronic pain (J. Pain 2005;113:340–6).
The mean duration of methadone maintenance treatment (MMT) was equivalent for the chronic pain and non-chronic pain groups. The patients completed a cross-sectional survey on chronic pain, and all met addiction criteria similar to the DSM-IV criteria for dependence on multiadministrations of heroin for at least 1 year.
Dr. Peles and her colleagues defined chronic pain as lasting 6 months or longer, and chronic severe pain was defined as pain of moderate to very severe intensity. Urine samples taken 1 month before the study and during the first month of treatment were analyzed for cocaine metabolites, opiates, benzodiazepines, cannabis, amphetamines, and methadone, and “the threshold for positive urine for benzodiazepines was higher than the therapeutic range,” they said.
There was no significant difference between the two groups in terms of Axes I and II: Axis I disorders were seen in 54% of chronic pain patients and 47% of non-chronic pain patients, while Axis II disorders were seen in 72% and 71%, respectively.
Pain was present before admission in 63.8% of the patients, and after MMT in 36.2%. However, duration of MMT was not related to pain duration or severity.
MMT dose was associated with pain severity and pain duration. The mean methadone dose was 147.1 mg/day for the 76 non-chronic pain patients, 134.6 mg/day for 12 patients with mild chronic pain, 159.8 mg/day for 38 patients with moderately severe pain, 175.5 mg/day for the 22 patients with severe pain, and 176.7 mg/day for the 22 patients with very severe pain.
The 26 patients with chronic pain for over 10 years got the highest methadone doses (182.1 mg/day). The 59 patients with pain for 1–10 years received 160.9 mg/day; doses of 134.2 mg/day went to patients with pain of less than 1 year. The researchers noted, however, “that methadone treatment was not initiated or directed toward pain relief.”
According to Dr. Peles and her associates, “it is probable that such high dosages of methadone may also be beneficial for pain, regardless of the primary indication for the treatment and the regimen of administration, which differed from that indicated for pain (i.e., once daily and not every few hours).”
Some MMT patients were given take-home dosages for the week, and against clinic directions, may have split their high doses, which might have reduced pain, the researchers speculated. Patients may also have misinterpreted pain as a withdrawal symptom, which may have led to requests for increased doses. Patients taking higher doses also may have built up a tolerance to the methadone.
Current positive urine test for benzodiazepines, and positive antibody to hepatitis C, correlated with significantly higher methadone doses. Benzodiazepine abuse may start as a form of self-medication to relieve pain, but the investigators suggested that it might also be that abuse of these drugs is a cause of “repeated rather than chronic pain.”
“We cannot conclude from these analyses whether or not pain was a cause or a consequence of the drug abuse,” said Dr. Peles and her associates.