An animal model for assessing pain-on-injection of antibiotics.

The paw-licking response of rats to a subplantar injection of an antibiotic was used as an indicator of the pain caused by that antibiotic. Good agreement with clinical findings was obtained with cefoxitin, cephalothin, cephradine, cefazolin, cephaloridine, and carbenicillin. Incorporation of a local anesthetic into the diluent of an irritating antibiotic reduced the number of paw-licking episodes. This rat paw model offers a simple and rapid means of estimating pain-on-injection following intramuscular injection of antibiotics to humans and may be applicable to other drugs as well.