Acute phase protein concentrations following serial procaine penicillin G injections in horses.
Authors: Gordon Danielle L, Foreman Jonathan H, Connolly Sara L, Schnelle Amy N, Fan Timothy M, Barger Anne M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Acute Phase Proteins and Procaine Penicillin Injections Interpreting acute phase protein (APP) concentrations to identify inflammation in horses requires careful consideration of confounding factors—including the injections themselves used to deliver treatment. This prospective study examined whether intramuscular procaine penicillin G (PPG), administered twice daily for five days, triggered an acute phase response in six healthy horses through measurement of creatine kinase (CK), aspartate aminotransferase (AST), fibrinogen (FIB), serum amyloid A (SAA), and haptoglobin (HAP) over a 30-day monitoring period. Muscle-derived markers showed the most pronounced response: CK increased 3.5–5.9 times baseline (from 200 to 723–1177 IU/L) on Days 1–6, whilst AST remained elevated through Day 10, peaking at 307–437 IU/L compared to a baseline of 233 IU/L. Traditional APPs demonstrated a delayed response—fibrinogen rose modestly on Days 6–8 and Day 10 (234–252 mg/dL from 177 mg/dL baseline), and SAA showed significant elevation only on Day 6 (113 μg/mL from baseline 4.7 μg/mL). Haptoglobin did not change significantly. These findings highlight that serial IM injections generate a measurable acute phase response, predominantly through tissue injury markers; when interpreting APP concentrations in treated horses, clinicians must distinguish injection-induced inflammation from pathological inflammation, particularly if samples are collected within 10 days of starting parenteral antimicrobials.
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Practical Takeaways
- •Intramuscular procaine penicillin G injections trigger measurable acute phase protein responses in horses, with CK and AST remaining elevated for up to 6-7 days post-injection; this must be considered when interpreting bloodwork from treated horses
- •Clinicians should be aware that serial IM antibiotic injections may confound interpretation of acute phase proteins used to detect systemic inflammation or infection in horses
- •These findings highlight the need for pre-injection baseline bloodwork if acute phase proteins will be used for clinical monitoring during or immediately after a course of IM procaine penicillin G therapy
Key Findings
- •Creatine kinase (CK) was significantly elevated above baseline (200±74 IU/L) on Days 1-6 (723-1177±355-544 IU/L, p<0.001 to p=0.02)
- •Aspartate aminotransferase (AST) was significantly increased above baseline (233±58 IU/L) on Days 2-7 and Day 10 (307-437±79-146 IU/L, p<0.001 to p=0.05)
- •Fibrinogen was significantly elevated above baseline (177±30 mg/dL) on Days 6-8 and Day 10 (234-252±33-49 mg/dL, p=0.02 to p=0.03)
- •Serum amyloid A was significantly increased above baseline (4.7±2.9 µg/mL) on Day 6 (113±186 µg/mL, p=0.02); haptoglobin showed no significant changes