Background: Dezocine is a powerful analgesic that can be less addictive than morphine, yet how
the two drugs interact in vivo is poorly understood. Here we administered dezocine alone or in
combination with morphine to different acute nociception paradigms to explore the interactions
of the 2 drugs upon co-administration.
Objective: To evaluate how dezocine interacts with morphine in different acute nociception
paradigms.
Study Design: Laboratory animal study.
Setting: Zhejiang University School of Medicine, Hangzhou, China.
Methods: Healthy mice were treated with saline, dezocine (0.625 – 2.5 µg), or a combination
of dezocine with morphine (2.5 µg). Tail withdrawal latency (TWL) was analyzed prior to and 30
minutes after drug administration. Rats were treated with saline, morphine (3 mg/kg), dezocine (3
mg/kg), or a combination of both drugs. The animals were then left uninjured, subjected to plantar
incision, or underwent formaldehyde-induced acute inflammation. Nociception was then analyzed
in terms of mechanical threshold (MT) to von Frey stimulation and paw withdrawal latency (PWL)
to thermal stimulation. Formaldehyde-induced pain score was calculated based on the duration of
biting and elevating of the animal’s legs. Phosphorylation of extracellular signal-regulated kinase
(pERK) was also measured after plantar incision as a molecular index of nociception.
Results: Dezocine enhanced TWL but inhibited morphine analgesia in a dose-dependent fashion
in mice. Usage of morphine or dezocine alone in uninjured rats increased MT, but co-administering
both drugs did not further increase MT. Usage of one drug alone, and both drugs together
increased MT and PWL relative to saline at 30 minutes after incision. Usage of one drug alone, but
not both drugs together, increased MT and PWL at 120 minutes after incision. Dezocine reduced
formaldehyde-induced nociception but co-administering both drugs did not further reduce pain
behavior.
Limitations: The results were obtained from animal study; clinical investigations will be needed
to clarify their interaction.
Conclusion: Dezocine antagonizes morphine analgesia on acute nociception upon simultaneous
administration.
Key words: Dezocine, morphine, acute nociception, analgesia