Placebo-controlled comparison of a morphine/dextromethorphan combination with morphine on experimental pain and hyperalgesia in healthy volunteers.
In this double-blind, placebo-controlled, crossover study we compared the analgesic effect of a single oral dose of 30-mg dextromethorphan and 30-mg morphine combination (MS/DM) to 30 mg morphine (MS) alone and either placebo or 30 mg dextromethorphan (DM) on cutaneous sensitization induced by heat/capsaicin (topical) sensitization on the forearm and the brief thermal sensitization model on the thigh in 22 healthy volunteers. Outcome measures were areas of secondary hyperalgesia to brush and von Frey hair stimulation in both sensitization models and the painfulness of acute thermal noxious stimulation on the upper arm. Compared with placebo, both MS/DM and morphine had some effect on the secondary hyperalgesia and reduced the painfulness of a noxious thermal stimulus. The analgesic effect of MS/DM was not superior to that of morphine on any outcome measure. These results differ from preclinical studies with animal experimental pain models in which DM markedly potentiated the analgesic effects of opioids, but they are in accordance with recent clinical trials for chronic pain.


CONCLUSIONS
Adding dextromethorphan to morphine (1:1 ratio) did not enhance analgesia on measures of experimental cutaneous sensitization and acute noxious thermal stimulation in healthy volunteers. The results differ from preclinical studies but agree with clinical trials. Human experimental models of pain and neuronal sensitization, which are responsive to oral opioids, allow efficient study of opioid combination analgesics and simplify the process for determining the optimal dose and/or dose ratio.
Frymoyer
Adam R
AR
UCSF Pain Clinical Research Center, Department of Neurology, University of California San Francisco, San Francisco, CA 94115, USA.
Rowbotham
Michael C
MC
Petersen
Karin Lottrup
KL
D000328:Adult; D000701:Analgesics, Opioid / Q000009:adverse effects / Q000627:therapeutic use*; D002211:Capsaicin; D003915:Dextromethorphan / Q000009:adverse effects / Q000627:therapeutic use*; D004311:Double-Blind Method; D004338:Drug Combinations; D004357:Drug Synergism; D005260:Female; D005542:Forearm; D006358:Hot Temperature; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000009:adverse effects / Q000627:therapeutic use*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy*; D013848:Thigh
D000701:Analgesics, Opioid; D004338:Drug Combinations; D003915:Dextromethorphan; D009020:Morphine; D002211:Capsaicin