A non-invasive and quantitative method for the study of tissue injury caused by intramuscular injection of drugs in horses.

The research is about a non-invasive way to quantify tissue damage in horses caused by intramuscular injections, using phenylbutazone as the injecting agent. It provides a method to measure the weight of muscle destroyed after injections, utilizing the creatine kinase (CK) disposition parameters.

Study Design & Methods

• The experiment was performed on six horses using intravenous and intramuscular administration of a creatine kinase (CK) horse preparation. This CK preparation was specific to horses and used to measure the CK release pattern after a controlled muscle injury.
• Phenylbutazone (PBZ), a potentially irritating substance, was administered via intravenous and intramuscular pathways, specifically targeting the neck and hindquarter areas.
• Data collected was analysed with compartmental models, and the instantaneous CK flux was calculated using a discrete deconvolution method. This method was used to analyse and interpret the data as it helped to understand the maximum CK entry rate after the administration of PBZ, providing a clearer picture of the extent of muscle damage.

Results

• For a CK dose of 150 U/kg, the results showed that the steady-state volume distribution was 0.050 +/- 0.0115 L/kg and the plasma half-life was 112 +/- 18 mins.
• The terminal phase half-life after CK intramuscular administration was 11.8 +/- 5.3 hours. It was observed that there was a flip-flop process indicating that the CK absorption rate was less than the elimination rate.
• The bioavailability of CK was close to 100% after intramuscular administration.
• The CK activity significantly increased after PBZ intramuscular administration, with peak values after neck and gluteal injections.
• By measuring the total CK released from injured muscle, they calculated that the equivalent of 0.044 +/- 0.029 g/kg of muscle was destroyed following PBZ administration in the neck and 0.118 +/- 0.048 g/kg after intragluteal PBZ administration.

Conclusions

• The research concluded that observing the CK release pattern after muscular damage provides a non-invasive approach to quantifying muscle damage in horses.
• The calculation of CK input rate by deconvolution has potential interest in describing events at the muscle cell level post PBZ administration.
• The research presents a viable means to quantify tissue injury following an intramuscular injection, which might provide a safer approach to drug administration in horses in the future.