Analgesic effects of antibiotics in rats.

Studies in forelimb-deafferented rats suggest that treatment with certain antibiotics can decrease pain sensation. To test this hypothesis, the analgesic effects of nine randomly selected antibiotics were studied in rats by using a constant-temperature hotplate. The results show that several antibiotics have antinociceptive properties, and two of them, chloramphenicol and ampicillin, can produce analgesia in a dose range used in human therapy (100 mg/kg). This analgesia is comparable to salicylate and ketoprofen analgesia but lower than pethidine's one. The analgesia is long lasting with chloramphenicol (10 h or more). These antinociceptive properties cannot be attributed to sedation because amphetamine-induced hyperactivity, measured in an open field, is not sensitive to injection of the most sensitive antibiotics.