Abstract
We read with great interest, the recent article in Laboratory Animals by IIbäck et al. (2008). This research adds to the growing research data on buprenorphine as an analgesic in laboratory rodents. The authors’ thoughtful discussion helped put their findings in perspective. As we read the article, however, we felt a couple of points deserved further clarification:
First, our article (Gades et al. 2000) was incorrectly cited as having administered a single dose of oral buprenorphine to rats, producing an analgesic effect of 6-8 h. We administered all the opioids in our study subcutaneously. The purpose of our study (Gades et al. 2000) was to determine the magnitude and duration of the analgesic effect of three commonly used opioids: buprenorphine (0.5 mg/kg for rats; 2.0 mg/kg for mice), butorphanol (2.0 mg/kg for rats; 5.0 mg/kg for mice) and morphine (10 mg/kg for rats and mice). We used two standard tests, the hot plate and tail flick assays, to measure opioid analgesia in 62 male Sprague-Dawley rats weighing 200-300 g and 61 male ICR mice weighing 25-35 g. We obtained five baseline measurements and then administered the drugs subcutaneously. Morphine gave the highest analgesic effect and was intermediate in duration (2-3 h in rats and mice) of analgesia. Butorphanol provided the lowest level of and shortest (1-2 h in rats and mice) analgesia. Buprenorphine had an intermediate analgesic effect and the longest duration (6-8 h in rats and 3-5 h in mice). In light of our results, we recommend the use of morphine (with frequent redosing) for severe pain, butorphanol for mild pain of short duration and buprenorphine for mild to moderate pain of increased duration. The dosing intervals suggested by our study are 2-3 h for morphine in both rats and mice, 1-2 h for butorphanol in both rats and mice, 6-8 h in rats and 3-5 h in mice for buprenorphine.
We concur with IIbäck et al. that oral buprenorphine in rodents is not efficacious, however, more appropriate citations would be the studies conducted by Martin et al. (2001) and Thompson et al. (2004, 2006) which showed that oral administration of buprenorphine recommended for postoperative analgesic care does not induce significant analgesia and therefore is not as effective as the standard subcutaneous dose of 0.05 mg/kg.
In summary, the results and conclusions shown by IIbäck et al. (2008) are noteworthy and add to our knowledge about the use of buprenorphine in laboratory rodents. They highlight the fact that oral administration of buprenphine is not as effective as parenteral administration in rodents; however, our study (Gades et al. 2000) did not administer buprenorphine orally to rats but subcutaneously only.