Objective—To evaluate the analgesic efficacy of ABT-116, a transient receptor potential cation channel vanilloid subfamily V member 1 antagonist, and compare it with that of buprenorphine by measurement of mechanical and thermal nociceptive thresholds in dogs.
Animals—Six 7- to 8-month-old dogs (3 males and 3 females).
Procedures—In a crossover study design, all dogs received ABT-116 (30 mg/kg, PO) and buprenorphine (0.03 mg/kg, orotransmucosally), with each treatment separated by 1 week. Physiologic variables were recorded prior to and 1, 6, and 24 hours after drug administration. Thermal (thoracic) and mechanical (dorsolateral aspect of the radius [proximal] and dorsopalmar aspect of the forefoot [distal]) nociceptive thresholds were assessed prior to (baseline) and 15 minutes and 1, 2, 4, 6, 12, 18, and 24 hours after treatment.
Results—Buprenorphine administration resulted in higher overall thermal and proximal mechanical nociceptive thresholds, compared with ABT-116. Distal mechanical nociceptive thresholds after treatment were higher than baseline values for both treatments, but the magnitude of change was greater for buprenorphine at 1 hour after administration. Whereas HR and RR sporadically differed from baseline values after ABT-116 administration, rectal temperature increased from a baseline value of 39 ± 0.2°C (mean ± SD) to a peak of 40.6 ± 0.2°C at 6 hours.
Conclusions and Clinical Relevance—In dogs without inflammation or nerve injury, PO administration of ABT-116 did not consistently result in an increase in nociceptive thresholds. However, clinically relevant increases in rectal temperature were identified after ABT-116 administration.
Objective—To evaluate composition of aqueous
humor obtained from normal eyes of llamas (Lama
glama) and alpacas (Lama pacos).
Sample Population—Aqueous humor obtained from
10 male llamas and 10 male alpacas.
Procedure—All animals had normal eyes, as determined
by ocular examination. Aqueous humor samples
were obtained via paracentesis of the anterior
chamber of animals that were heavily sedated.
Chemical analysis included measurement of concentrations
of sodium, potassium, magnesium, chloride,
bicarbonate, phosphorus, and glucose as well as
osmolality and pH.
Results—With the exception of potassium concentrations,
values for aqueous humor composition did
not differ significantly between llamas and alpacas.
Mean ± SD values for llamas and alpacas, respectively,
were: sodium, 154.7 ± 2.1 and 152.7 ± 2.1 mEq/L;
potassium, 5.3 ± 0.4 and 4.6 ± 0.4 mEq/L; magnesium,
1.8 ± 0.1 and 1.7 ± 0.1 mg/dl; chloride, 130.0 ±
1.6 and 127.0 ± 3.3 mEq/L; bicarbonate, 19.2 ± 1.5
and 20.2 ± 2.3 mEq/L; phosphorous, 2.7 ± 0.3 and 2.5
± 0.4 mg/dl; glucose, 80.3 ± 3.9 and 80.8 ± 7.3 mg/dl;
total protein, 29.0 ± 8.6 and 31.5 ± 10.1 mg/dl; and
osmolality, 305.8 ± 11.8 and 306.2 ± 4.9 mOsm. The
pH ranged from 7.5 to 8.0 for both species.
Potassium concentrations were significantly higher in
llamas than alpacas.
Conclusions and Clinical Relevance—Except for
potassium, composition of aqueous humor did not
differ significantly between llamas and alpacas.
Aqueous humor composition of llamas and alpacas is
similar to that of other species that have been examined.
(Am J Vet Res 2001;62:1060–1062)
Objective—To compare the disposition of lidocaine
administered IV in awake and anesthetized horses.
Procedure—After instrumentation and collection of
baseline data, lidocaine (loading infusion, 1.3 mg/kg
administered during 15 minutes (87 µg/kg/min); constant
rate infusion, 50 µg/kg/min) was administered IV
to awake or anesthetized horses for a total of 105 minutes.
Blood samples were collected at fixed times during
the loading and maintenance infusion periods and
after the infusion period for analysis of serum lidocaine
concentrations by use of liquid chromatography with
mass spectral detection. Selected cardiopulmonary
parameters including heart rate (HR), mean arterial
pressure (MAP), arterial pH, PaCO2, and PaO2 were also
recorded at fixed time points during lidocaine administration.
Serum lidocaine concentrations were evaluated
by use of standard noncompartmental analysis.
Results—Serum lidocaine concentrations were higher
in anesthetized than awake horses at all time points
during lidocaine administration. Serum lidocaine concentrations
reached peak values during the loading
infusion in both groups (1,849 ± 385 ng/mL and
3,348 ± 602 ng/mL in awake and anesthetized horses,
respectively). Most lidocaine pharmacokinetic variables
also differed between groups. Differences in cardiopulmonary
variables were predictable; for example,
HR and MAP were lower and PaO2 was higher in anesthetized
than awake horses but within reference
ranges reported for horses under similar conditions.
Conclusions and Clinical Relevance—Anesthesia
has an influence on the disposition of lidocaine in horses,
and a change in dosing during anesthesia should
be considered. (Am J Vet Res 2005;66:574–580)
Objective—To determine the oral bioavailability, single and multidose pharmacokinetics, and safety of silibinin, a milk thistle derivative, in healthy horses.
Animals—9 healthy horses.
Procedures—Horses were initially administered silibinin IV and silibinin phospholipid orally in feed and via nasogastric tube. Five horses then consumed increasing orally administered doses of silibinin phospholipid during 4 nonconsecutive weeks (0 mg/kg, 6.5 mg/kg, 13 mg/kg, and 26 mg/kg of body weight, twice daily for 7 days each week).
Results—Bioavailability of orally administered silibinin phospholipid was 0.6% PO in feed and 2.9% via nasogastric tube. During the multidose phase, silibinin had nonlinear pharmacokinetics. Despite this, silibinin did not accumulate when given twice daily for 7 days at the evaluated doses. Dose-limiting toxicosis was not observed.
Conclusions and Clinical Relevance—Silibinin phospholipid was safe, although poorly bio-available, in horses. Further study is indicated in horses with hepatic disease.
Objective—To evaluate antioxidant capacity and inflammatory cytokine gene expression in horses fed silibinin complexed with phospholipid.
Animals—5 healthy horses.
Procedures—Horses consumed increasing orally administered doses of silibinin phospholipid during 4 nonconsecutive weeks (0 mg/kg, 6.5 mg/kg, 13 mg/kg, and 26 mg/kg of body weight, twice daily for 7 days each week). Dose-related changes in plasma antioxidant capacity, peripheral blood cell glutathione concentration and antioxidant enzyme activities, and blood cytokine gene expression were evaluated.
Results—Plasma antioxidant capacity increased throughout the study period with increasing dose. Red blood cell nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase I activity decreased significantly with increasing doses of silibinin phospholipid. No significant differences were identified in glutathione peroxidase activity, reduced glutathione or oxidized glutathione concentrations, or expression of tumor necrosis factor α, interleukin-1, or interleukin-2.
Conclusions and Clinical Relevance—Minor alterations in antioxidant capacity of healthy horses that consumed silibinin phospholipid occurred and suggest that further study in horses with liver disease is indicated.
Objective—To determine whether infusion of xylazine and ketamine or xylazine and propofol after sevoflurane administration in horses would improve the quality of recovery from anesthesia.
Animals—6 healthy adult horses.
Procedures—For each horse, anesthesia was induced by administration of xylazine, diazepam, and ketamine and maintained with sevoflurane for approximately 90 minutes (of which the last 60 minutes were under steady-state conditions) 3 times at 1-week intervals. For 1 anesthetic episode, each horse was allowed to recover from sevoflurane anesthesia; for the other 2 episodes, xylazine and ketamine or xylazine and propofol were infused for 30 or 15 minutes, respectively, after termination of sevoflurane administration. Selected cardiopulmonary variables were measured during anesthesia and recovery. Recovery events were monitored and subjectively scored.
Results—Cardiopulmonary variables differed minimally among treatments, although the xylazine-propofol infusion was associated with greater respiratory depression than was the xylazine-ketamine infusion. Interval from discontinuation of sevoflurane or infusion administration to standing did not differ significantly among treatments, but the number of attempts required to stand successfully was significantly lower after xylazine-propofol infusion, compared with the number of attempts after sevoflurane alone. Scores for recovery from anesthesia were significantly lower (ie, better recovery) after either infusion, compared with scores for sevoflurane administration alone.
Conclusions and Clinical Relevance—Xylazine-ketamine or xylazine-propofol infusion significantly improved quality of recovery from sevoflurane anesthesia in horses. Xylazine-ketamine or xylazine-propofol infusions may be of benefit during recovery from sevoflurane anesthesia in horses for which a smooth recovery is particularly critical. However, oxygenation and ventilation should be monitored carefully.
This study aims to assess intrathecal mepivacaine for euthanasia in anesthetized horses and compare it to a traditional euthanasia method using a single intravenous injection of pentobarbital in sedated horses.
Client-owned horses and horses requiring euthanasia due to involvement in concurrent research projects were used. Horses were randomly assigned to 1 of 2 groups: intrathecal mepivacaine after anesthesia or intravenous pentobarbital after sedation. All horses had normal vital parameters and no signs of infectious disease at the time of euthanasia.
The intrathecal mepivacaine group was anesthetized before the intrathecal injection of mepivacaine. The pentobarbital group was sedated, concurrently anesthetized and euthanized using intravenous pentobarbital, then received an intrathecal saline (0.9% NaCl) solution injection to a blind observer. Both groups were sedated with detomidine and the time from sedation to the cessation of vital parameters (respirations, pulse, corneal reflex, and ECG) was recorded. Euthanasias were recorded for review by a blinded anesthesiologist, using an independent scale to assess the quality of sedation, anesthesia induction, and lateral recumbency.
Time from detomidine administration to cessation of each vital parameter was significantly longer in the intrathecal mepivacaine group. There was no statistically significant difference in qualitative scores between groups for sedation or induction, but lateral recumbency was subjectively superior in the anesthetized intrathecal mepivacaine group.
Intrathecal mepivacaine provided a safe, effective, alternative method of euthanasia to intravenous pentobarbital and addresses concerns about barbiturate availability. This study also informs practitioners of what to expect (ie, longer cessation of vital parameters) when using the intrathecal mepivacaine method.
A 36-kg (79-lb) castrated male Greyhound (dog 1) and a 25-kg (55 lb) spayed female Greyhound (dog 2) underwent general anesthesia for dental care with similar perianesthetic protocols on multiple occasions from 2013 to 2016. Both dogs had periodontal disease but were otherwise deemed healthy. Both dogs developed clinically relevant hyperkalemia, with signs including loss of P waves on ECG tracings, during multiple anesthetic events.
Dog 1 developed hyperkalemia during 2 of 2 anesthetic events, with ECG changes noted during the first event. Dog 2 developed hyperkalemia during 3 of 4 anesthetic events, with ECG changes identified during the second and third events. Serum potassium concentration for both dogs was within the reference range prior to and between anesthetic events. No underlying etiopathogenesis for hyperkalemia was identified for either dog.
TREATMENT AND OUTCOME
In each hyperkalemic event, the clinician stopped the dental procedure and continued to provide supportive care and monitoring while the dog recovered from anesthesia. The ECG changes resolved, and serum potassium concentration returned to the reference range rapidly after inhalant anesthetic administration was discontinued. The dogs were discharged from the hospital without further complications.
Hyperkalemia in anesthetized Greyhounds resulted in serious cardiac conduction abnormalities, which could be potentially fatal if not recognized and promptly treated. Further investigation into the etiopathogenesis, prevention and treatment strategies, and genetic or familial components of this condition is indicated.