Atracurium besylate, a nondepolarizing neuromuscular blocking agent, was administered as an infusion to 8 anesthetized cats in which neuromuscular blockade was assessed, using the train-of-four response. Once 50% depression of the first-twitch (T1) response was achieved, the infusion was held constant for 60 minutes before being discontinued and the recovery time was determined. The time for recovery was recorded as the time for the train-of-four ratio (T4 ratio) to increase from 50% to 75%. After recovery, atracurium infusion was reinstituted and the cats were again maintained for 60 minutes at 50% depression. A single bolus of gentamicin sulfate (2.0 mg/kg of body weight) was administered IV, and the infusion was continued for another 60 minutes before it was discontinued and the time for recovery was recorded. Within 1 minute of gentamicin administration, the mean +/= SD T1 response decreased from 49 +/- 5% to 33 +/- 8% of baseline and the T4 ratio decreased from 28 +/- 19% to 14 +/- 11%. Peak effect occurred at 5 minutes, with a T1 response of 29 +/- 6% of baseline and a T4 ratio of 13 +/- 12%. By 60 minutes after gentamicin administration, the T1 response had increased to 38 +/- 7% of baseline and the T4 ratio had increased to 21 +/- 13%. The time for recovery significantly (P less than 0.03) increased from 9.9 +/- 3.4 minutes during the control study to 18.1 +/- 10.7 minutes during the gentamicin study. In this study, gentamicin potentiated the neuromuscular blockade induced by atracurium and increased the recovery time. Residual blockade, observed after gentamicin administration was reversed with edrophonium.

Anesthesia was induced in 8 healthy llamas by administration of guaifenesin and ketamine, and was maintained with halothane in oxygen. On 2 separate experimental days, atracurium was given to induce 95 to 99% reduction of evoked hind limb digital extensor tension (twitch). For the first part of the study, atracurium was given iv as repeat boluses, with muscle twitch strength being allowed to return without intervention to 75% of baseline after each bolus before the subsequent bolus was given. A total of 5 bolus doses of atracurium was given. For the first bolus, 0.15 mg/kg of body weight iv, and for subsequent boluses, 0.08 mg/kg, induced desired relaxation. Onset of relaxation was slightly more rapid for repeat, compared with initial, bolus. Duration of relaxation and recovery time were similar to initial and repeat doses. Maximal twitch reduction was observed in 4 +/- 0.2 minutes (mean +/- SEM). Duration from maximal twitch reduction to 10% recovery was 6.3 +/- 0.4 minutes. Twitch recovery from 10 to 50% of baseline took 11.6 +/- 0.6 minutes. Twitch recovery from 10 to 75% recovery took 19.5 +/- 1.1 minutes. Recovery from 10% twitch to 50% fade took 12.8 +/- 0.5 minutes. Fade at 50% recovery of twitch was 39 +/- 0.02%. Significant (P < 0.05) animal-to-animal variation was observed in twitch recovery times. For the second part of the study, atracurium was initially given IV as a 0.15-mg/kg bolus, followed by infusion for 1 to 2 hours. Infusion rate required some early adjustment to maintain desired relaxation, but the rate that prevailed was 1.07 +/- 0.07 ml/kg/h (0.4 mg of atracurium/ml of saline solution). Recovery of muscle twitch was similar to that previously mentioned for repeat bolus administration, At the end of the study, edrophonium (0.5 mg/kg) with atropine (0.01 mg/kg, IV) was effective in antagonizing residual neuromuscular blockade by atracurium. All llamas recovered without injury from anesthesia, although 1 llama had a rough recovery. It was concluded that atracurium can provide neuromuscular blockade by either repeat bolus administration or continuous infusion in llamas.

Atracurium besylate, a nondepolarizing neuromuscular blocking agent, was administered to 24 isoflurane-anesthetized domestic chickens. Birds were randomly assigned to 4 groups, and atracurium was administered at dosage of 0.15, 0.25, 0.35 or 0.45 mg/kg of body weight. The time of onset of twitch depression, the amount of maximal twitch depression, and the duration of muscular relaxation were recorded. After return to control twitch height, atracurium was further administered to achieve > 75% twitch depression. When twitch depression reached 75% during noninduced recovery, 0.5 mg of edrophonium/kg was administered to reverse the muscle relaxation. Throughout the experimental period, cardiovascular, arterial blood gas, and acid-base variables were monitored. The effective dosage of atracurium to result in 95% twitch depression in 50% of birds, (ED95/9595) was calculated, using probit analysis, to be 0.25 mg/kg, whereas the ED95/95 the dosage of atracurium to result in 95% twitch depression in 95% of birds, was calculated by probit analysis to be 0.46 mg/kg. The total duration of action at dosage of 0.25 mg/kg was 34.5 +/- 5.8 minutes; at the highest dosage (0.45 mg/kg), total duration increased to 47.8 +/- 10.3 minutes. The return to control twitch height was greatly hastened by administration of edrophonium. Small, but statistically significant changes in heart rate and systolic blood pressure, were associated with administration of atracurium and edrophonium. These changes would not be clinically relevant. In this study, atracurium was found to be safe and reliable for induction of muscle relaxation in isoflurane anesthetized chickens.

The effect of pancuronium bromide (0.025 mg/kg. B.W.) alone or combined with diazepam (1mg/Kg. I.V) were evaluated in six adult ewes. Pancuronium bromide alone exhibited a muscle relaxants effect, but without analgesia. All baseline measurements were taken before the administration the anesthetic agent and were repeated at 5,10,15,20 and 25 min. intervals after induction an aesthesia alone or combination with diazepam . it was found that heart rate decreased at 5 min.,but respiratory rate did change at 5-25 min. and it was significantly at 15,20 and 25 min. Pancuronium bromide – diazepam combination is responsible for declined respiratory rate and decumbency position in early stage. Pancuronium bromide – diazepam induce effective and safe an aesthesia for periods 45 minutes, due to competitive diazepam as a sedative effect of muscle relaxation. Adequate strength and duration of analgesia due to prevent impulse transmission histamine and ensured rapid and safe recovery

Effects of the neuromuscular blocking agent succinylcholine (n = 9), the centrally acting skeletal muscle relaxant diazepam (n = 11), and the direct-acting skeletal muscle relaxant dantrolene sodium (n = 8) on the urethral pressure profile were evaluated in anesthetized, healthy, sexually intact, adult male cats. Intravenous administration of succinylcholine (0.075 mg/kg of body weight) significantly decreased mean absolute pressure in the prostatic and post-prostatic/penile intraurethral segments by -9.5 and -6.5 mm of Hg, respectively (P = 0.0002 and P = 0.0006, respectively). Dantrolene (1.0 mg/kg, IV) significantly decreased mean prostatic and postprostatic/ penile intraurethral segmental pressures by -3.5 and -2.8 mm of Hg, respectively (P = 0.005 and P = 0.0181, respectively). Diazepam (0.8 mg/kg, IV) did not significantly alter mean intraurethral segmental pressures. None of the drugs caused a change in segmental lengths of the urethra. These results indicate that skeletal muscle makes a substantial contribution to intraurethral tone in anesthetized, healthy, sexually intact male cats and that skeletal muscle relaxation may be successful in reducing prostatic and post-prostatic/penile urethral segmental tone in male cats. These results also suggest that dantrolene sodium may be valuable for the pharmacologic management of urethral disorders in male cats.

Anesthesia was induced in 8 healthy llamas by administration of guaifenesin and ketamine, and was maintained with halothane in oxygen. On 2 separate experimental days, atracurium was given to induce 95 to 99% reduction of evoked hind limb digital extensor tension (twitch). For the first part of the study, atracurium was given iv as repeat boluses, with muscle twitch strength being allowed to return without intervention to 75% of baseline after each bolus before the subsequent bolus was given. A total of 5 bolus doses of atracurium was given. For the first bolus, 0.15 mg/kg of body weight iv, and for subsequent boluses, 0.08 mg/kg, induced desired relaxation. Onset of relaxation was slightly more rapid for repeat, compared with initial, bolus. Duration of relaxation and recovery time were similar to initial and repeat doses. Maximal twitch reduction was observed in 4 +/- 0.2 minutes (mean +/- SEM). Duration from maximal twitch reduction to 10% recovery was 6.3 +/- 0.4 minutes. Twitch recovery from 10 to 50% of baseline took 11.6 +/- 0.6 minutes. Twitch recovery from 10 to 75% recovery took 19.5 +/- 1.1 minutes. Recovery from 10% twitch to 50% fade took 12.8 +/- 0.5 minutes. Fade at 50% recovery of twitch was 39 +/- 0.02%. Significant (P < 0.05) animal-to-animal variation was observed in twitch recovery times. For the second part of the study, atracurium was initially given IV as a 0.15-mg/kg bolus, followed by infusion for 1 to 2 hours. Infusion rate required some early adjustment to maintain desired relaxation, but the rate that prevailed was 1.07 +/- 0.07 ml/kg/h (0.4 mg of atracurium/ml of saline solution). Recovery of muscle twitch was similar to that previously mentioned for repeat bolus administration, At the end of the study, edrophonium (0.5 mg/kg) with atropine (0.01 mg/kg, IV) was effective in antagonizing residual neuromuscular blockade by atracurium. All llamas recovered without injury from anesthesia, although 1 llama had a rough recovery. It was concluded that atracurium can provide neuromuscular blockade by either repeat bolus administration or continuous infusion in llamas.

On the basis of results in dogs, conditioning exercise may increase sensitivity to nondepolarizing muscle relaxants. Five Thoroughbreds were exercised/conditioned 3 times weekly on a treadmill for 8 months. Increasing maximal rate of O2 consumption verified that the horses were responding to exercise conditioning. Six nonexercised Thoroughbreds served as the control group. Studies were done with horses under general anesthesia by use of halothane during partial paralysis by a brief constant-rate infusion with the muscle relaxant, metocurine iodide. Quantification of degree of paralysis of the hoof twitch (eg, digital extensor) occurred with simultaneous quantification of blood values of metocurine. Pharmacokinetic and pharmacodynamic analyses of the data were done by a nonlinear regression program, using the Hill equation. There were no differences in findings between exercised and nonexercised horses. The mean blood concentration for the 50% paralyzing dose of metocurine was 0.44 +/- 0.11 (SD) micrograms/ml in exercised horses, and 0.58 +/- 0.22 micrograms/ml in nonexercised horses. Despite evidence for a response to conditioning, a significant change in the sensitivity of the neuromuscular junction to metocurine was not found.

Atracurium besylate, a nondepolarizing neuromuscular blocking agent, was administered to 24 isoflurane-anesthetized domestic chickens. Birds were randomly assigned to 4 groups, and atracurium was administered at dosage of 0.15, 0.25, 0.35 or 0.45 mg/kg of body weight. The time of onset of twitch depression, the amount of maximal twitch depression, and the duration of muscular relaxation were recorded. After return to control twitch height, atracurium was further administered to achieve > 75% twitch depression. When twitch depression reached 75% during noninduced recovery, 0.5 mg of edrophonium/kg was administered to reverse the muscle relaxation. Throughout the experimental period, cardiovascular, arterial blood gas, and acid-base variables were monitored. The effective dosage of atracurium to result in 95% twitch depression in 50% of birds, (ED95/9595) was calculated, using probit analysis, to be 0.25 mg/kg, whereas the ED95/95 the dosage of atracurium to result in 95% twitch depression in 95% of birds, was calculated by probit analysis to be 0.46 mg/kg. The total duration of action at dosage of 0.25 mg/kg was 34.5 +/- 5.8 minutes; at the highest dosage (0.45 mg/kg), total duration increased to 47.8 +/- 10.3 minutes. The return to control twitch height was greatly hastened by administration of edrophonium. Small, but statistically significant changes in heart rate and systolic blood pressure, were associated with administration of atracurium and edrophonium. These changes would not be clinically relevant. In this study, atracurium was found to be safe and reliable for induction of muscle relaxation in isoflurane anesthetized chickens.