Meropenem synovial fluid concentrations after intravenous regional limb perfusion in standing horses.
Authors: Fontenot Robin L, Langston Vernon C, Zimmerman Jamie A, Wills Robert W, Sloan Pearce B, Mochal-King Cathleen A
Journal: Veterinary surgery : VS
Summary
Intravenous regional limb perfusion (IVRLP) is an established technique for delivering high antibiotic concentrations to distal limb structures, yet optimal dosing strategies remain unclear. This experimental study in nine standing mares evaluated synovial fluid and plasma concentrations of meropenem following 500 mg administration via IVRLP to the forelimb, with joint fluid sampling over an 18-hour period and quantification using microbiological bioassay. Peak synovial concentrations occurred rapidly (median 0.5 hours post-injection) but showed marked variability between individuals (mean maximum 25.6 µg/mL, range <limit of detection to 75.5 µg/mL), with clinically effective levels (>1 µg/mL) persisting for only 3 hours (observed median) to 4.1 hours (predicted mean), and concentrations above 6 µg/mL maintained for approximately 2 hours. For time-dependent beta-lactam antibiotics like meropenem—which require prolonged drug exposure above the minimum inhibitory concentration—these findings suggest that a single 500 mg dose via IVRLP may provide insufficient duration of therapeutic activity within the 24-hour dosing interval, potentially inadequate for preventing resistance development in susceptible pathogens. Practitioners should consider whether higher doses, more frequent IVRLP treatments, or alternative antimicrobial approaches may be warranted for equine synovial infections, particularly those involving potentially resistant organisms where robust pharmacodynamic exposure is critical.
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Practical Takeaways
- •Standard 500 mg meropenem IVRLP dosing achieves therapeutic levels for only 2-3 hours, which may be insufficient for joint infection prevention or treatment in standing procedures
- •High inter-horse variability in synovial concentrations means some horses may receive subtherapeutic levels—consider higher doses or modified protocols for standing regional perfusions
- •If using IVRLP for joint surgery or infection risk, discuss alternative dosing strategies (higher doses, repeat dosing, or recumbent techniques) with your veterinarian rather than relying on single 500 mg injection
Key Findings
- •Meropenem synovial fluid concentrations peaked at 0.5 hours post-IVRLP with mean maximum of 25.6 µg/mL but showed high variability (range below quantitation to 75.5 µg/mL)
- •Concentrations remained above susceptibility breakpoint (1 µg/mL) for median 3 hours, well below the typical 24-hour dosing interval
- •High concentrations (>6 µg/mL) were maintained for only 2 hours median, suggesting inadequate duration for time-dependent antibiotic efficacy
- •Current 500 mg IVRLP dosing may be ineffective and could promote antibiotic resistance if time-dependent pharmacodynamics apply