Non-invasive method for the study of local muscle reactions after intramuscular (IM) injection of an antibiotic in horses

This study describes muscle reactions to intramuscular injection of an antibiotic through ultrasonography and serum creatine kinase (CK) concentrations in horses. Three adult horses from the Equine Centre, Universiti Putra Malaysia were used. An advance real-time B-mode ultrasound machine conected to a linear array multifrequency (5-8 MHz)transducer was used throughout the study. Ultrasonographic examination was done before and after IM injections at approximately 6, 24, 48 and 72 hours and at 3-day intervals until the muscle structure returned to normal. Blood samples were obtained before IM injection and at 6, 24, 48 and 72 hours post-injection, and serum CK concentrations were measured. There were localised increased echogenicity or hyperechoic structures at site of drug deposition. The muscle returned to normal appearance after approximately 2 weeks of post-injection. In one horse, the drug was detected to be deposited intermuscularly. Serum CK analysis seems to increase after 24 hours of injection. Muscle reaction to IM injection of antibiotics can be defined ultrasonographically and the progress of muscle reactions until recovery to the normal muscle structures can be monitored with ultrasound. A slight increase in serum CK concentrations after antibiotic injection indicated that the drug used in this study did not cause significant damage to the muscle of these horses. Ultrasonography provides a clear definition of the location of drug deposition within the muscle and could be used as a meaningful diagnostic tool for monitoring of muscle reactions to IM injections of drugs.