Abstract
Postoperative pain management in laboratory animals is important for animal welfare and required under law in many countries. Frequent injection of analgesics to rodents after surgery is stressful for the animals and labour-intensive for animal care personnel. An alternative dosing scheme such as administration of analgesics in the drinking water would be desirable. However, the efficacy of a chronic oral analgesic treatment via this route has not yet been documented. This study investigated the antinociceptive efficacy of buprenorphine administered ad libitum via the drinking water of laboratory rats. The antinociceptive efficacy of buprenorphine in drinking water was compared with repeated subcutaneous injections. A comparison was also made between buprenorphine in drinking water and the combination of one single subcutaneous injection of buprenorphine followed by buprenorphine in drinking water. Antinociception was assessed by use of an analgesiometric model measuring the rats' latency time to withdrawal from a noxious heat stimulus applied to the plantar surface of the paw. Results revealed that buprenorphine in drinking water (0.056 mg/mL) induced significant increases in paw withdrawal latency times during a three-day period of administration with a maximal effect at 39 h after the start of buprenorphine administration. One single injection of buprenorphine (0.1 mg/kg s.c.) followed by buprenorphine in the drinking water (0.056 mg/mL) induced an earlier onset of antinociception than buprenorphine in drinking water alone. In contrast, buprenorphine (0.1 mg/kg s.c.) injected every 8 h over a period of three days did not result in significant increases in paw withdrawal latency times. In conclusion, our results suggest that one single subcutaneous injection of buprenorphine followed by buprenorphine in drinking water may be a viable treatment option for the relief of pain in laboratory rats, but at the doses used in this study in pain-free rats it was associated with a decrease in water intake and some behavioural changes.