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SUMMARY

Objective

To evaluate effects of a single high dose of gentamicin on neuromuscular function in horses anesthetized with halothane.

Animals

6 healthy adult horses.

Procedure

Halothane-anesthetized horses were positioned in left lateral recumbency, and the right hind limb was immobilized in a reusable fiberglass cast fixed to a steel frame. The hoof was attached to a force transducer, and resting tension of 0.93 ± 0.16 kg was maintained. A supramaximal train-of-four stimulus of 2 Hz for a duration of 0.25 millisecond was applied to the superficial peroneal nerve every 20 seconds by a square-wave stimulator. The force of the evoked digital extensor tension was recorded to determine first muscle twitch tension, compared with the baseline value (T1%) and the ratio of the force of the fourth twitch to the first twitch (T4/T1). Data were recorded at 5, 10, 15, 30, and 60 minutes after IV administration of vehicle or gentamicin (6 mg/kg of body weight).

Results

There was a significant (P = 0.04) treatment-time interaction for the effect of gentamicin on T1%; T1% associated with vehicle decreased from 100% to 92% during the 60- minute study period, but no decrease was associated with gentamicin. For T4/T1, there was no significant effect of treatment or time or treatment-time interaction between gentamicin and vehicle.

Conclusions

Gentamicin did not cause a decrease in initial muscular strength, nor did it impair the muscles’ ability to sustain strength.

Clinical Relevance

A single high dose of gentamicin does not cause significant neuromuscular blockade when administered alone to healthy horses anesthetized with halothane. (Am J Vet Res 1997;58:1324–1326)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine pharmacokinetics, renal effects, and effect on atracurium-induced neuromuscular blockade of a high dose of gentamicin in isoflurane-anesthetized dogs.

Animals

6 healthy, adult, mixed-breed dogs, anesthetized twice and receiving gentamicin (6 mg/kg of body weight, IV) or saline solution.

Procedure

Blood samples were collected before and at intervals after gentamicin administration. Pharmacokinetic values were evaluated by use of multivariant stepwise linear regression analysis. Gentamicin-induced renal changes were assessed by comparing pretreatment and 12- to 24-hour posttreatment values for serum urea nitrogen, serum creatinine, urine creatinine-to-γ-glutamyltransferase ratio, and urinalysis. Neuromuscular blockade, maintained by atracurium infusion, was assessed, using the train-of-four response. At stable 50% depression of first twitch (T1) gentamicin or saline solution was given. Before and at posttreatment intervals for 60 minutes, T1% and fourth twitch-to-T1 ratio were recorded. The infusion was discontinued and 50 to 75% T1 recovery time was recorded. At 75% T1, edrophonium (0.5 mg/kg) was administered IV.

Results

Mean values for volume of distribution and clearance were 0.263 L/kg and 2.0 ml/min/kg, respectively. Mean maximal serum concentration of gentamicin was 46.4 μg/ml. Pre and posttreatment values for serum urea nitrogen, serum creatinine, urine creatinine-to-γ-glutamyltransferase ratio, and other urine analytes were not significantly different. Mean (± SD) values for T1% and fourth twitch-to-T1 ratio decreased significantly after gentamicin (depression was maximal at 5 minutes). Recovery time (50 to 75% T1) was not different between groups. Edrophonium restored twitch to baseline.

Conclusions

Mean values for apparent volume of distribution and total body clearance of gentamicin were similar to values in unanesthetized dogs. Mean maximal serum concentration of gentamicin was greater than that in unanesthetized dogs. Renal function was unaffected. Gentamicin potentiated atracurium-induced neuromuscular blockade, but did not affect recovery time. (Am J Vet Res 1996;57:1623–1626)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate disposition of butorphanol after IV and IM administration, effects on physiologic variables, and analgesic efficacy after IM administration in llamas.

Design—Nonrandomized crossover study.

Animals—6 healthy adult male llamas.

Procedure—Butorphanol (0.1 mg/kg [0.045 mg/lb] of body weight) was administered IM first and IV 1 month later. Blood samples were collected intermittently for 24 hours after administration. Plasma butorphanol versus time curves were subjected to pharmacokinetic analysis. Two months later, butorphanol (0.1 mg/kg) was administered IM, and physiologic variables and analgesia were assessed.

Results—Extrapolated peak plasma concentrations after IV and IM administration were 94.8 ± 53.1 and 34.3 ± 11.6 ng/ml, respectively. Volume of distribution at steady state after IV administration was 0.822 ± 0.329 L/kg per minute and systemic clearance was 0.050 ± 0.014 L/kg per minute. Slope of the elimination phase was significantly different, and elimination half-life was significantly shorter after IV (15.9 ± 9.1 minutes) versus IM (66.8 ± 13.5 minutes) administration. Bioavailability was 110 ± 49% after IM administration. Heart rate decreased and rectal temperature increased. Somatic analgesia was increased for various periods. Two llamas became transiently sedated, and 2 became transiently excited after butorphanol administration.

Conclusions and Clinical Relevance—Although IV administration of butorphanol results in a short halflife that may limit its analgesic usefulness, the elimination half-life of butorphanol administered IM is likely to be clinically useful. The relationship among plasma butorphanol concentration, time, and analgesia differed with the somatic analgesia model; clinically useful analgesia may occur at lower plasma concentrations than those reported here. (J Am Vet Med Assoc 2001;219:1263–1267)

Full access
in Journal of the American Veterinary Medical Association

SUMMARY

Objective

To determine the cardiovascular effects of buprenorphine in isoflurane-and halothane-anesthetized dogs.

Animals

6 healthy adult hound-type dogs given buprenorphine (16 μg/kg of body weight, IV) or isovolumetric 5% dextrose solution during anesthesia with isoflurane or halothane.

Procedure

Each dog was anesthetized 4 times, with a minimum of 10 days between episodes. Anesthesia was induced with isoflurane or halothane in O2 by mask, and was maintained with 1.9% isoflurane or 1.3% halothane (end-tidal concentration). The Paco2 was maintained between 35 and 45 mm of Hg by use of mechanical ventilation, and the following variables were determined: systolic, diastolic, and mean arterial blood pressures; cardiac output; cardiac index; stroke volume; heart rate; systemic vascular resistance; mean pulmonary arterial pressure; and pulmonary vascular resistance. In addition, arterial blood samples for gas and acid-base analyses were collected at 30-minute intervals for 2.5 hours. After baseline values were recorded, dogs were randomly assigned to receive either buprenorphine (16 μg/kg, IV) or isovolumetric 5% dextrose solution. All variables were then recorded at 15-minute intervals for 2.5 hours.

Results

During isoflurane anesthesia, buprenorphine administration caused significant (P < 0.05) reductions in diastolic arterial pressure, mean arterial pressure, systolic arterial pressure, cardiac index, and heart rate, whereas systemic vascular resistance increased significantly. During halothane anesthesia, buprenorphine administration caused significant decreases in heart rate, cardiac index, mean, systolic and diastolic arterial blood pressures, and stroke volume, whereas pulmonary arterial blood pressure and systemic vascular resistance increased significantly.

Conclusion

Although the changes seen were significant, they were not sufficiently large to be of clinical importance in healthy dogs. (Am J Vet Res 1997;58:1280–1284)

Free access
in American Journal of Veterinary Research

Objective

To evaluate adequacy of analgesia provided by postoperative administration of butorphanol to cats undergoing onychectomy.

Design

Randomized controlled trial.

Animals

63 cats undergoing elective onychectomy.

Procedure

Cats were randomly assigned to a treatment (n = 42) or control group (21). Cats in the treatment group were given butorphanol parenterally immediately and 4 hours after surgery and orally for 2 days after surgery. Rectal temperature, heart rate, and respiratory rate were recorded and scores were assigned for temperament, recovery, sedation, analgesia, and lameness for the first 24 hours after surgery. Owners provided scores for appetite, personality, and lameness the first and second days after discharge from the hospital.

Results

Heart rate, respiratory rate, rectal temperature, and temperament and sedation scores were not significantly different between groups at any evaluation time. Recovery scores were significantly better for butorphanol-treated than for control-group cats 10 minutes after extubation. Analgesia scores were significantly better for butorphanol-treated than for control-group cats between 5 and 24 hours after surgery. Fewer butorphanol-treated than control-group cats were lame at the time of discharge from the hospital. The first day after discharge, owners reported that percentages of butorphanol-treated cats that ate normally, acted normally, and had only mild or no lameness were significantly higher than percentages of control-group cats that did. Significant differences between groups were not detected the second day after discharge.

Clinical Implications

Results suggest that for cats undergoing onychectomy, administration of butorphanol the day of surgery and the first full day after surgery provides effective analgesia and improves recovery, appetite, and gait. (J Am Vet Med Assoc 1998;213:246-250)

Free access
in Journal of the American Veterinary Medical Association