The disposition of gentamicin in equine plasma, synovial fluid and lymph.

The research article investigates the dispersion of the antibiotic gentamicin in equine plasma, synovial fluid, and lymph, following its intravenous administration. The findings indicate that its concentration in lymph is highest and lasts the longest while its elimination from synovial fluid is the slowest.

Study Design and Procedure

• The study was divided into two trials, each involving different collection techniques and timings.
• In the first trial, a lymph vessel in a horse’s hindlimb was cannulated. The day after surgery, plasma and lymph samples were collected over a 12-hour period after injection of gentamicin sulphate.
• The second trial, around 48 hours post-surgery, involved catheterizing the fetlock joint of the same hindlimb, with plasma, synovial fluid, and lymph samples collected for 12 hours following a similar intravenous injection.

Results of Kinetic Parameters

• Derived kinetic parameters showed that the movement and reactions of gentamicin in body fluids did not vary between the two trials.
• In both plasma and lymph, gentamicin initially showed similar concentrations. However, 2-3 hours after injection, lymph concentrations were on average 60% higher than the plasma concentrations.
• While the concentration in these two fluids showed parallel trends, gentamicin elimination was significantly slower in lymph than in plasma.

Disposition in Synovial Fluid

• On average, gentamicin dispersion in synovial fluid appeared slower than in both plasma and lymph. The mean lymph-to-synovial fluid and plasma-to-synovial fluid ratios 2-4 hours after injection, exhibited a lymph bias.
• After the 3-hour mark, the concentration in synovial fluid had limited predictive value for tissue fluid concentrations. However, plasma concentrations offered a viable index for prediction.

Utility of Lymph Cannulation

• The study concluded that lymph cannulation could serve as a valuable technique for antibiotic disposition studies.
• A sample of any of the three fluids, taken 3 hours after injection, was shown to be representative of the others. This point led to the conclusion that lymph cannulation could be a feasible method to study antibiotic dispersion.