Morphine synovial fluid concentrations after intravenous regional limb perfusion in horses during standing sedation

Background Addition of morphine to the perfusate while performing intravenous regional limb perfusion (IVRLP) may be helpful in treating painful infectious orthopaedic conditions of the distal limb. Objectives The main objective of this study was to determine synovial morphine concentrations following IVRLP with morphine alone or in combination with amikacin. Study design Randomised cross‐over in vivo experiment. Methods Six horses underwent IVRLP with 0.1 mg/kg morphine sulphate diluted to 60 mL using 0.9% NaCl (M group) or combined with 2 g amikacin and 0.9% NaCl (MA group) with a 2‐week washout period between treatments. Synovial fluid was collected from the radiocarpal joint (RCJ) at 10, 20, 30, 120, 240, 480, 720 and 1440 min after IVRLP. The tourniquet was removed after the 30‐min sample was collected. Synovial concentrations of morphine and major metabolites were measured using liquid chromatography–tandem mass spectrometry. Amikacin concentrations were quantified by a fluorescence polarisation immunoassay. Results Measurable concentrations of morphine were apparent in the RCJ of all horses. Median C MAX of morphine in the M group was 4753.1 (2115.7–14 934.5) ng/mL and 4477 (3434.3–7363) ng/mL in the MA group ( p = 0.5). Median C MAX of synovial amikacin was 322.6 (157.5–1371.6 μg/mL). Main limitations Limitations include small sample size. Investigators were not blinded to the treatments and a third treatment group where amikacin alone was administered via IVRLP to the study population was not included. Conclusions IVRLP using morphine is a feasible technique and synovial morphine concentrations were measurable following IVRLP and were not affected when used concurrently with amikacin. Administration of morphine via IVRLP may be beneficial as an analgesic technique for orthopaedic conditions of the distal limb while limiting potential serious systemic side‐effects.