Histopathological lesions following intramuscular administration of saline in laboratory rodents and rabbits

This review was undertaken to assess the nature and incidence of procedure-related changes in mice, rats and rabbits which received saline solution by intramuscular injection. Data were collected on the injection sites from 7 studies representing 152 animals. The original observations by the different study pathologists from both control and treated animals were evaluated in order to create a glossary of preferred terms to be used in toxicology studies. These standardized terms were then applied to changes observed in the saline-treated animals. The review showed that the most severe of the procedure-related lesions were only of a slight level. Two days post-injection, the local reactions were mainly composed of minimal infiltration by mononuclear cells (lymphocytes and macrophages) with occasional degeneration of myofibres. From 10 to 42 days post-injection, lesions showed regeneration of myofibres and some fibrosis. In rats, the number of injections at each site influenced inflammatory infiltrate and degenerative lesions.