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No Effect on SAA Response Linked to Penicillin G or Flunixin in Healthy Horses

By Landon Gray

There does not appear to be an associated effect on serum amyloid A (SAA) response in healthy adult horses treated with procaine penicillin G (PPG) given in multiple injections sites and/or flunixin meglumine, according to data shared at the 69th annual meeting of the American Association of Equine Practitioners.

The researchers decided to look at PPG after elective procedures, because “we usually give high volume PPG in the muscle,” which theoretically could damage it, said Jurica Trsan, DMV, a large animal internal medicine specialist at the David and Bonnie Brunner Purdue Veterinary Medical Hospital, in West Lafayette, Ind.

“As you know, flunixin meglumine reduces inflammation, and we don’t know actually, [the effects] PPG—or any kind of intramuscular injections—causes,” Dr. Trsan said.

Administering PPG or flunixin during an elective procedure should not alter the SAA kinetics.

Crossover Study

The researchers aimed to evaluate the effect of PPG and/or flunixin meglumine on SAA response in healthy horses when used at clinical dosing regimens. They conducted a crossover design study and enrolled 6 healthy adult horses. The study had 4 arms:

1. PPG group (intramuscularly every 12 hours for 72 hours),

2. flunixin meglumine group (IV every 24 hours for 72 hours),

3. a combined PPG (intramuscularly every 12 hours for 72 hours) and flunixin meglumine group (IV every 24h for 72 hours) and

4. a control group.

PPG Injections alternated between the right and left neck, right and left semitendinosus muscles. Flunixin meglumine was given in the jugular vein.

The researchers collected blood at 0, 24, 48, 72, 96 and 120 hours after initial administration of the medications to measure SAA (washout period, 30 days). In the control group, they found that every horse except 1 had individual SAA values that were within the reference range (≤20 µg/mL). The 1 exception had a SAA value of 28 µg/mL at 72 hours.

Similarly, in the flunixin meglumine group, 5 horses showed normal SAA values, with 1 showing an SAA value of 24 µg/mL at 96 hours.

Five horses in the combined PPG and flunixin meglumine group also showed normal SAA values within the reference range, but the sixth had increased SAA values of 32 µg/mL to 45 µg/mL between 48 hours and 96 hours post-drug administration.

However, in the PPG alone group, all the horses displayed normal SAA values throughout the study.

No Differences

The researchers determined there was no difference in the area under the SAA time curve between the control and treatment groups (P>0.05). They concluded that there was no inflammatory response that induced an SAA value above the reference range in most healthy adult horses triggered by the administration of intramuscular PPG and/or IV flunixin meglumine.

Dr. Trsan noted the study was limited by the small sample size, potential carry-over risk and unforeseen environmental conditions.

“As a conclusion from our study, administration of PPG and/or flunixin meglumine during elective procedures should not alter the SAA kinetics, especially if given in multiple, [alternating] administration sites, and it shouldn't be attributed to PPG [or flunixin meglumine] if you have SAA elevation,” Dr. Trsan concluded. MeV

For more information:

Trsan J, Nottle BF, Pusterla N. Effect of procaine penicillin G and flunixin meglumine on serum amyloid A response in healthy adult horses. J Equine Vet Sci. 2023;129:104876. doi:10.1016/j.jevs.2023.104876. https:/pubmed.ncbi.nlm.nih.gov/37451522/