Effect of gentamicin sulfate and sodium bicarbonate on the synovium of clinically normal equine antebrachiocarpal joints

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Abstract
SUMMARY: The effect of gentamicin sulfate, unbuffered and buffered with sodium bicarbonate, on synovial fluid and membrane of clinically normal equine joints was evaluated. Thirty-six adult horses with clinically normal antebrachiocarpal joints were allotted to 6 treatment groups of 6 horses each. One antebrachiocarpal joint in each horse was chosen for treatment. Group-1 horses were given gentamicin (3 ml; 50 mg/ml); group-2 horses were given sodium bicarbonate (3 ml; 1 mEq/ml); group-3 horses were given gentamicin (3 ml; 50 mg/ml) and sodium bicarbonate (3 ml; 1 mEq/ml); group-4 horses were not treated; and horses of groups 5 and 6 were given polyionic physiologic solution (3 and 6 ml, respectively). Synovial fluid specimens were obtained from 5 horses of each group for cytologic analysis at postinjection hours (pih) 0, 24, 72, and 192 and for pH determination at pih 0, 0.25, 0.5, 1, 4, 8, 24, 72, and 192. The sixth horse of each group was euthanatized at pih 24, and the synovial membrane of the treated and contralateral (nontreated) antebrachiocarpal joints was examined macroscopically and microscopically. After intra-articular gentamicin administration, the mean synovial fluid pH was lowest (5.98) at pih 0.25, but by PIH 8, it was not significantly different from the control value (group-5 horses). When sodium bicarbonate was combined with gentamicin before intra-articular administration, the mean synovial fluid pH was lowest (7.07) at pih 0.25, but by pih 1, it was not significantly different from the control value (group-6 horses). The mean synovial fluid wbc count was significantly (P < 0.05) greater 24 hours after buffered gentamicin treatment (14,120 cells/μl) than after treatment with gentamicin alone (4,440 cells/μl), and predominantly large mononuclear cells were observed. Resolution of the cellular inflammatory response was observed by pih 72 after administration of buffered gentamicin or gentamicin alone. In all groups, significant difference in synovial fluid neutrophil or rbc count from control value (groups 5 and 6) was not observed. In horses of all age groups, appreciable difference in the macroscopic appearance of the light pink to salmoncolored mucosa of the synovial membrane was not detected between the treated and nontreated antebrachiocarpal joints. Synovitis was detected in the joint capsules treated with buffered gentamicin, unbuffered gentamicin, and sodium bicarbonate. In each instance, the palmarolateral pouch of the antebrachiocarpal joint was more inflamed than was the dorsal portion of the joint capsule, probably because the palmarolateral pouch was the site for placement of the catheter and intra-articular drug administration. The quality of the inflammation was more compatible with trauma or irritation than with sepsis.

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