Antinociceptive potency (ED50) of morphine and analogs in age-matched male and female Sprague-Dawley rats in the warm-water tail-withdrawal assay at 50°C
Rats received cumulative doses of the drug, and tail withdrawal was evaluated 30 min postinjection. Values represent the mean ± S.E.M. of six rats.
| Drug | ED50 | Ratio | |
|---|---|---|---|
| Male | Female | ||
| mg/kg | female/male | ||
| Fentanyl | 0.06 ± 0.002 | 0.06 ± 0.0004 | 1.0 |
| Oxymorphone | 0.18 ± 0.02 | 0.29 ± 0.06 | 1.6 |
| Hydromorphone* | 0.27 ± 0.03 | 0.42 ± 0.05 | 1.6 |
| Heroin | 0.62 ± 0.11 | 0.58 ± 0.06 | 0.9 |
| Methadone | 1.49 ± 0.20 | 1.81 ± 0.37 | 1.2 |
| Oxycodone | 1.53 ± 0.29 | 1.71 ± 0.30 | 1.1 |
| Morphine*** | 2.17 ± 0.25 | 6.08 ± 0.62 | 2.8 |
| Hydrocodone** | 2.23 ± 0.21 | 3.70 ± 0.37 | 1.7 |
| Codeine | 46.3 ± 10.4 | 46.6 ± 5.9 | 1.0 |
↵* P < 0.05, **P < 0.01, and ***P < 0.001 between male and female values.