Can coadministration of oxycodone and morphine produce analgesic synergy in humans? An experimental cold pain study.
OBJECTIVE
The coadministration of subantinociceptive doses of oxycodone with morphine has recently been shown to result in a synergistic antinociceptive effect in rats. The present study was aimed to investigate the possibility that coadministration of morphine and oxycodone can produce a similar synergistic effect in humans exposed to an experimental model of cold pressor test (CPT).


METHODS
The enriched enrollment design was used to exclude 'stoic' and 'placebo responders' in a single-blind fashion. 'Nonstoic', placebo 'nonresponder' female volunteers (n = 30) were randomly assigned to receive 0.5 mg kg(-1) oral morphine sulphate, 0.5 mg kg(-1) oral oxycodone hydrochloride, and the combination of 0.25 mg kg(-1) morphine sulphate with 0.25 mg kg(-1) oxycodone hydrochloride, 1 week apart from each other, in a double-blind crossover design. Latency to pain onset (threshold), pain intensity (VAS), and pain tolerance (time until removal of the hand from the water) were measured six times over a 3-h period, subsequent to the administration of each medication, and were used to assess their antinociceptive effect.


RESULTS
The combination produced a significantly higher effect on latency to pain onset than that of morphine alone [difference in mean postbaseline value 2.2; 95% confidence interval (CI) 0.48, 3.9; P = 0.01] but the effect was nonsignificantly smaller that that of oxycodone alone. Similarly, the effect of the combination on pain tolerance was significantly larger than that of morphine alone (combination difference 8.4; 95% CI 2.5, 14.3; P = 0.007), whereas oxycodone alone caused a nonsignificantly larger effect than that of the combination treatment. Comparisons of pain magnitude failed to show any significant differences between the three treatments.


CONCLUSIONS
These results indicate that at the doses tested, morphine and oxycodone do not produce synergistic antinociceptive effects in healthy humans exposed to the CPT.
Department of Anaesthesiology, Carmel Hospital, Haifa, Israel.
Michael
M
Grach
Wattan
W
Massalha
Dorit
D
Pud
Rivka
R
Adler
Elon
E
Eisenberg
D000293:Adolescent; D000328:Adult; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D003080:Cold Temperature; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004338:Drug Combinations; D004357:Drug Synergism; D005260:Female; D006801:Humans; D009020:Morphine / Q000008:administration & dosage*; D010098:Oxycodone / Q000008:administration & dosage*; D010146:Pain / Q000517:prevention & control*
D000701:Analgesics, Opioid; D004338:Drug Combinations; D009020:Morphine; D010098:Oxycodone