medwireNews: There is frequently a discrepancy between pain patients’ self-reported use of analgesic medication and the objective evidence from urine analysis of the drugs they are actually taking.
This is the conclusion of German researchers, who suggest that patients attending chronic pain centres should undergo routine toxicological drug monitoring.
Andreas Schwarzer (Ruhr University Bochum) and colleagues undertook a cross-sectional study to investigate the reliability of patients’ self-reported drug use.
They enrolled 243 consecutive outpatients attending their first appointment at a pain clinic and 100 patients with pain who were awaiting surgery (controls). All participants were asked to list their current medication and had blood and urine samples analysed for medication and metabolites.
The team identified a discrepancy between self-report and toxicological analysis in 35.6% of patients, and this was significantly more frequent among the pain clinic patients than controls (43.3 vs 24.0%).
The most frequent type of discrepancy was under-reporting of non-opioid analgesic use, found in 19.4% of pain patients and 12.0% of controls. There was also under-reporting of psychotropic drug use by 7.0% of pain patients and 8.0% of controls.
Over-reporting also occurred, primarily among patients from the pain clinic and concerning coanalgesics (4.1%) and opioid analgesics (4.1%).
In logistic regression analysis restricted to the pain clinic cohort, the presence of depression was a significant independent risk factor of over/under-reporting of medication use, with an odds ratio of 2.12.
Univariate analysis identified two further risk factors: reported use of opioid analgesics and pain lasting for longer than 40 months. Patients with two or three of these risk factors had a significantly increased risk of over/under-reporting, with an odds ratio of 4.92.
Writing in Pain Physician, Schwarzer and colleagues say that it is surprising, in view of recent worries about increasing opioid use and misuse, that the majority of incorrect reports concerned non-opioid analgesic drugs. Indeed, just 3% of cases of under-reporting related to opioid drugs.
“Nevertheless this is a disquieting fact because of the large spectrum of adverse effects of these substances [non-opioid analgesics],” they write.
They conclude: “Therefore, toxicological drug monitoring in comprehensive pain centers is indispensable.”
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