Results from thermal quantitative sensory testing may be associated with the efficacy of imipramine for pain relief in patients with chronic low back pain, according to a recent study published in the European Journal of Pain.
No other quantitative sensory testing results were found to predict the efficacy of oxycodone or clobazam relative to the active placebo tolterodine in the study.
In this crossover trial, participants with chronic low back pain underwent electrical, pressure, and thermal quantitative sensory testing at baseline and 1 to 2 hours after treatment with oxycodone 15 mg (n=50), imipramine 75 mg (n=50), clobazam 20 mg (n=49), or active placebo tolterodine 1 mg. Pain intensity was evaluated with a Numeric Rating Scale every 30 minutes for up to 2 hours after treatment.
Participants had a minimum washout period of 1 week between treatment and active placebo sessions. The association between results from baseline quantitative sensory testing and pain relief after 2 hours was evaluated. Known alleles for drug metabolism and pain perception were genotyped to determine whether some variants could be used to predict a certain treatment’s efficacy for pain relief.
Overall, imipramine treatment was not found to improve pain scores at any time point relative to placebo. Baseline thermal quantitative sensory testing thresholds were associated with the efficacy of imipramine after 2 hours in the sitting position (P =.004 for the leg and P =.003 for the arm) and in the supine position (P =.006 for the leg and P <.001 for the arm). Participants who were more sensitive to heat or cold pain had greater low back pain relief by imipramine.
The following alleles were shown to affect pain relief in the sitting position after treatment with imipramine: the μ-opioid receptor A118G allele (P =.047) and the catechol-o-methyltransferase high-pain-sensitivity genotype (P =.05), although multiple testing removed significance for both associations.
Although oxycodone was shown to have a significant analgesic effect relative to placebo, no quantitative sensory test results or genetic variants were found to be associated with pain relief from the drug. Results were similar with clobazam, which was associated with analgesic effects relative to placebo in the supine position. Study participants who were not sensitive to heat were more responsive to placebo and patients who were more heat-sensitive were found to have improved pain relief with clobazam.
The study authors concluded that, “none of the selected [quantitative sensory testing] measures could be identified as a predictor of analgesic effect of oxycodone or clobazam,” and that, ”patients more sensitive to heat and cold pain respond better to imipramine.” They added that, “none of the candidate genes involved in pain sensitivity or drug metabolism seemed to be a predictor of drug effect.”
Schliessbach J, Siegenthaler A, Bütikofer L, et al. Predicting drug efficacy in chronic low back pain by quantitative sensory tests [published online January 23, 2018]. Eur J Pain. doi: 10.1002/ejp.1183