Concurrent intravenous regional limb perfusion and systemic amikacin administration achieves variable synovial fluid amikacin concentrations in healthy neonatal foals.

Objective: To evaluate plasma and synovial fluid amikacin concentrations following cephalic or saphenous IV regional limb perfusion (IVRLP) with a dosing protocol of 25 mg of amikacin/kg, divided into 16.7 mg/kg systemically and 8.3 mg/kg regionally. We hypothesized that plasma amikacin concentrations observed at 30 minutes after systemic administration would exceed a therapeutic target of 53 μg/mL and that synovial fluid concentrations would exceed a therapeutic target of 80 μg/mL.

Methods: Over a 5-month period (spring/summer of 2023), 8 healthy neonatal foals were administered each protocol at least 48 hours apart. Synovial fluid was obtained 30 minutes after IVRLP. The systemic amikacin dose was administered at the time of tourniquet release (30 minutes), and plasma samples were obtained over a 24-hour period.

Results: The observed synovial fluid and plasma amikacin concentrations were not different between protocols, so a single least square means estimate was predicted for each sample type, at each time point. The amikacin concentration estimate in synovial fluid was 238.5 μg/mL (95% CI, 146.1 to 330.9) 30 minutes after IVRLP and in plasma was 66.3 μg/mL (95% CI, 57.5 to 75.1) 30 minutes after administration of the systemic dose. Some foals did not reach the synovial fluid therapeutic target in all joints studied.

Conclusions: These results support our hypotheses and suggest that administering amikacin systemically and via IVRLP as described can achieve therapeutic plasma and synovial fluid concentrations in neonatal foals.

Clinical relevance: Concurrent systemic and IVRLP administration of amikacin as described can be clinically effective in the treatment of sepsis with concurrent septic arthritis in neonatal foals.