Tolerance to fentanyl in neonatal rats after a 72-hr infusion of fentanyl (100 μg/kg/hr) from osmotic minipumps
| Treatment | ED50 | Potency Ratio |
|---|---|---|
| μg/kg (95%, C.L.) | (95% C.L.) | |
| Naive | 19 (10–39) | – |
| Saline pump (1 μl/hr) | 23 (15–35) | vs. Naive 0.9 (0.6–1.6) |
| Fentanyl pump (100 μg/kg/hr) | 86 (50–145)* | vs.saline pump 4.1 (2.2–6.8)* |
PND6 rats remained naive or were implanted with an osmotic minipump containing saline or fentanyl. Three days later, the rats were tested for antinociception in the tail-flick test 10 min after s.c. administration of fentanyl.
* Significantly different from saline pump-implanted rats.