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

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.

The main objective of this study was to determine synovial morphine concentrations following IVRLP with morphine alone or in combination with amikacin.

Randomised cross-over in vivo experiment.

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.

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).

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.

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.