INTERACTION OF GENTAMICIN AND ATRACURIUM IN ANESTHETIZED HORSES

Evoked hind limb digital extensor tension (hoof twitch) was maintained at 40% of baseline for 1 h by atracurium infusion in 7 horses anaesth etised with halothane. After 1 h, atracurium was discontinued and hoof twitch allowed to recover to 75%. Atracurium was again given by infus ion to maintain 40% twitch for a second hour, then 2 mg gentamycin/kg bwt were given i.v. Atracurium infusion was continued for a third hour , and then hoof twitch was again allowed to recover spontaneously to 7 5%. Gentamycin reduced twitch strength from 40 +/- 1 % (mean +/- sem) to 29 +/- 4% within 7.0 +/- 1.5 min (P = 0.02). Twitch gradually retur ned to pre-gentamycin strength over the course of the next hour. Recov ery of hoof twitch from 50% to 75% took 7.7 +/- 0.7 min for atracurium alone and 11.5 +/- 2.7 min for atracurium plus gentamycin (P = 0.03). Recovery from 50% twitch to 75% fade recovery took 13.8 +/- 0.8 min f or atracurium alone and 13.7 +/- 1.2 min for atracurium plus gentamyci n. At 75% recovery of fade, hoof twitch was 87 +/- 3% for atracurium a lone and 82 +/- 4% for atracurium plus gentamycin. Reversal of the blo ck with edrophonium and subsequent recovery of the horses from anaesth esia were uneventful. It was concluded that, although gentamycin did a ugment the neuromuscular blockade of atracurium, the effect was minima l.