| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 2533858 | European Journal of Pharmacology | 2010 | 5 Pages |
Methadone used for opioid dependence therapy is associated with increased pain sensitivity. This study aimed to investigate whether methadone administration lowers nociceptive threshold in adult male Sprague-Dawley (SD) rats, and if this threshold could be altered by the NMDA receptor antagonist memantine. Rats were implanted with osmotic pumps delivering 1 mg/kg/day methadone (n = 6), or saline placebo (n = 6) (0.51 μl/h). A separate cohort of rats received either methadone 1 mg/kg/day (n = 8) or methadone 1 mg/kg/day with 20 mg/kg/day memantine (n = 8). Nociception was measured by the Hargreave's paw withdrawal test. Baseline nociception was measured on day 0 prior to osmotic pump implantation and was measured daily for the following 21 days. Osmotic pumps were removed following nociceptive testing on day 14. Methadone only treated rats had a mean paw withdrawal latency significantly lower than the corresponding values for saline on days 8, 9, 10, 11, 12, 14, and 17 (P < 0.05). At all other time points the mean paw withdrawal latency was not significantly different from saline (P > 0.05). Paw withdrawal latency of rats treated with methadone co-administered with memantine did not differ significantly compared to methadone only (P > 0.05). This demonstrates that methadone induces hyperalgesia in the SD rat yet this hyperalgesia resolves following discontinuation of methadone administration. Furthermore, memantine does not alter the development of methadone-induced hyperalgesia.
