Influence of a single oral dose of trazodone on intradermal histamine reactivity in clinically healthy dogs

BACKGROUND

Drug interactions are significant considerations for intradermal testing (IDT). Trazodone (TRZ) is an anxiolytic and selective histaminergic (H1 ) antagonist with no interaction in human prick tests; however, interaction in canine IDT is unknown.

HYPOTHESIS/OBJECTIVES

Trazodone will not adversely affect intradermal histamine reactions in dogs.

ANIMALS

Fourteen nonanxious, nonatopic, healthy client-owned dogs were enrolled in this randomised, blinded, cross-over study.

MATERIALS AND METHODS

Dogs were randomised to receive low-dose TRZ (4 mg/kg) (Teva Pharmaceuticals), high-dose TRZ (8 mg/kg) or no TRZ per os two hours before intravenous sedation with dexmedetomidine (5 mcg/kg) (Dexdomitor; Zoetis). Intradermal testing was performed with five quadrupling dilutions of histamine (1:100,000 to 1:25,600,000 w/v; Greer) and 0.9% saline (Hospira), observing a minimum two weeks washout period between treatments. Two observers, who were blinded to treatment and the identity of the injections, evaluated each test using previously established subjective and objective methods.

RESULTS

The mean wheal diameter of histamine 1:1,600,000 w/v was significantly smaller with low-dose TRZ (4 mg/kg) compared to the control group (p = 0.048; repeated measures ANOVA with post hoc Tukey's test). For all other histamine dilutions and saline, mean wheal diameter was not significantly different among groups. There were no significant differences in the subjective scores of all histamine dilutions and saline (p > 0.05; Friedman test).

CONCLUSION AND CLINICAL RELEVANCE

A single oral dose of TRZ does not adversely affect intradermal histamine reactions in dogs.

Effects of trazodone administration on the neurologic examination in healthy dogs

BACKGROUND

Trazodone is an anxiolytic used PO to decrease anxiety in dogs. Whether or not trazodone affects the neurologic examination in dogs has not been previously reported.

OBJECTIVE

Investigate whether trazodone administration is associated with changes in the neurologic examination in healthy dogs.

ANIMALS

Thirty-two healthy dogs between 1 and 6 years old with no previously diagnosed medical conditions and perceived by their owners as neurologically normal.

METHODS

Baseline sedation and anxiety assessments and neurologic examination were performed on each dog, followed by trazodone administration (6.25-8.60 mg/kg PO). The sedation and anxiety assessments and neurologic examination were repeated 2.5 hours after trazodone administration. The examinations were performed by a single board-certified veterinary neurologist and were video-recorded. The videos were randomized and reviewed by a different neurologist, blinded to the previous evaluations, who scored the examinations.

RESULTS

Seven of 32 (22%) dogs had worse scores on their neurologic examination after receiving trazodone, manifesting as new or progressive PR deficits. Although not clinically relevant, 18.7% of the dogs had consciousness levels that changed from bright, alert, responsive to quiet, alert, responsive after trazodone administration. No other changes were observed on neurologic examination. Sedation and anxiety scores were significantly different after trazodone administration compared to before (P < .001 and P < .001, respectively).

CONCLUSIONS AND CLINICAL IMPORTANCE

Most dogs did not have changes on neurologic examination after trazodone administration. However, approximately 20% of dogs had new or worsening PR deficits after receiving trazodone. Ideally, trazodone should not be given before neurologic examination in dogs.

The Effects of Prophylactic Dexmedetomidine Administration on General Anesthesia Recovery Quality in Healthy Dogs Anesthetized With Sevoflurane and a Fentanyl Constant Rate Infusion Undergoing Elective Orthopedic Procedures

To determine the effects of a dexmedetomidine slow bolus, administered prior to extubation, on recovery from sevoflurane-anesthesia and a fentanyl continuous rate infusion (CRI) in dogs undergoing orthopedic surgical procedures. Sixty-two client-owned, healthy dogs weighing 27.4 ± 11 kg undergoing elective orthopedic procedures were premedicated with: 0.1 mg/kg hydromorphone intramuscular, 0.05 mg/kg hydromorphone intravenously (IV) or 5 mcg/kg fentanyl IV. Following premedication, dogs were induced with propofol, administered locoregional anesthesia and maintained with sevoflurane and a fentanyl CRI (5-10 mcg/kg^/hr). Dogs were randomly assigned to one of two treatment groups: 0.5 mcg/kg dexmedetomidine (DEX) or 0.5 ml/kg saline (SAL). Following surgery, patients were discontinued from the fentanyl CRI and administered DEX or SAL IV over 10 min. Following treatment, dogs were discontinued from sevoflurane and allowed to recover without interference. Recoveries were video recorded for 5 min following extubation and assessed by two blinded anesthesiologists using a visual analog scale (VAS; 0-10 cm) and a numerical rating scale (NRS; 1-10). Mean arterial pressure (MAP), heart rate (HR), pulse oximetry (SpO₂), temperature, respiratory rate (RR), and end-tidal sevoflurane (EtSevo) and carbon dioxide (EtCO₂) concentrations were recorded at specific time-points from induction to 5 min post-bolus administration and analyzed using linear mixed models. Fentanyl, propofol, and hydromorphone dose and the time to extubation were compared using an unpaired t-test. Differences in recovery scores between groups were evaluated with a Mann-Whitney test. Data reported as mean ± SD or median [interquartile range] when appropriate. A p < 0.05 was significant. There were no significant differences between groups in fentanyl, propofol, and hydromorphone dose, duration of anesthesia, intraoperative MAP, HR, RR, SpO₂, temperature, EtCO₂, EtSevo or anesthetic protocol. MAP was higher in DEX compared to SAL at 10 (104 ± 27 and 83 ± 23, respectively) and 15 (108 ± 28 and 86 ± 22, respectively) min after treatment. DEX had significantly lower VAS [0.88 (1.13)] and NRS [2.0 (1.5)] scores when compared to SAL [VAS = 1.56 (2.59); NRS = 2.5 (3.5)]. Time to extubation (min) was longer for DEX (19.7 ± 11) when compared to SAL (13.4 ± 10). Prophylactic dexmedetomidine improves recovery quality during the extubation period, but prolongs its duration, in sevoflurane-anesthetized healthy dogs administered fentanyl.

Sedative Effects of Intramuscular Dexmedetomidine and Ketamine at Sub-Anesthetic Dose Alone or in Combination with Methadone in Healthy Dogs

The aim of the present study was to compare sedation quality and cardiorespiratory parameters in healthy dogs after intramuscular injection of dexmedetomidine and ketamine with or without methadone. Forty client-owned dogs were randomly divided into two groups and received IM dexmedetomidine (5 µg kg^-1) and ketamine (1 mg kg^-1), associated (DKM group) or not (DK group) with methadone (0.2 mg kg^-1). Sedation, heart rate (HR), respiratory rate (ƒ_R), mucous membrane and rectal temperature were recorded at baseline (T0) and after 5 (T5), 10 (T10) and 20 (T20) minutes. From T10, cardiac rhythm was monitored with a continuous lead II electrocardiogram. Ease of venous catheter placement, total propofol dose and any apnea episodes were recorded. Sedation was significantly greater in the DKM group, and a significant increase from T5 to T20 within DKM (P = .0002) and DK (P = .008) was also observed. Within each group, HR was significantly lower at all time points compared to baseline. No significant differences between groups were found in the number of arrhythmogenic events (atrioventricular blocks). In both group ƒ_R decreased over time. The propofol dose required for anesthesia induction was significantly lower (P = .027) in the DKM group. In conclusion, a good level of sedation was achieved in both groups, although this was greater in DKM. Smooth animal-operator interaction and ease of venous catheter placement showed that DK was a useful sedative protocol in healthy patients.

Pharmacokinetics and efficacy of trazodone following rectal administration of a single dose to healthy dogs

OBJECTIVE

To determine the pharmacokinetics and efficacy of trazodone following rectal administration of a single dose to healthy dogs.

ANIMALS

6 healthy adult dogs.

PROCEDURES

Each dog received a single dose of trazodone (approx 8 mg/kg) per rectum. Trazodone tablets were crushed into a powder, mixed with 5 mL of tap water, and injected into the rectum via a red rubber catheter. Sedation scores were assigned, and blood samples were collected for determination of plasma trazodone concentration at predetermined times before and after drug administration. Pharmacokinetic parameters were estimated by noncompartmental analysis.

RESULTS

Plasma trazodone concentration remained below the detection limit for 1 dog even though it became moderately sedate. Median (interquartile [25th to 75th percentile] range [IQR]) maximum plasma trazodone concentration and volume of distribution and clearance corrected for bioavailability were 1.00 μg/mL (0.66 to 1.40 μg/mL), 10.3 L/kg (7.37 to 14.4 L/kg), and 639 mL/kg/h (594 to 719 mL/kg/h), respectively. Median time to maximum plasma trazodone concentration and elimination half-life were 15 minutes (range, 15 to 30 minutes) and 12 hours (IQR, 7.99 to 12.7 hours), respectively. All dogs became mildly or moderately sedate, and the extent of sedation was maximal at a median of 30 minutes (IQR, 30 to 60 minutes) after trazodone administration. No adverse effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Rectal administration of trazodone may be a viable option for sedation and treatment of anxiety in dogs for which administration of sedatives and anxiolytics by other routes is contraindicated. Further research is necessary to better elucidate the pharmacokinetics and efficacy of trazodone following rectal administration and determine optimal dosing.

Effect of different anesthetic mixtures-ketamine-xylazine, ketamine-acepromazine and tiletamine-zolazepam-on the physiological and blood biochemistry parameters of male rhesus monkeys (Macaca mulatta) at different ages

BACKGROUND

Anesthetic agents are commonly utilized in the handling of non-human primates for prevent the stress caused in physical exploration or physical restrain. For this reason, the objective of this work was to describe the effect of age and dissociative anesthetics (ketamine and tiletamine), and their combinations with acepromazine, xylazine and zolazepam, on the physiological and blood biochemical parameters in Macaca mulatta.

METHODS

Eighty male Macaca mulatta were divided into four experimental groups depending on the anesthetic mixture applied. Each group of 20 males was divided into five sub-groups according to age. Physiological parameters were recorded every 5 minutes during a 30-minute period. A blood sample was drawn to analyze blood biochemistry.

RESULTS

Statistical analyses revealed significant differences in the physiological parameters between the ketamine-acepromazine and ketamine-xylazine groups compared to the control group. The analysis of blood biochemistry found significant differences by age and by anesthetic mixture among all groups.

CONCLUSION

These findings contribute to standardizing this animal model in biological research.

Determination of the pharmacokinetics of a single oral dose of trazodone and its effect on the activity level of domestic pigeons (Columba livia)

OBJECTIVE

To determine the pharmacokinetics of a single oral dose of trazodone and its effect on the activity of domestic pigeons (Columba livia).

ANIMALS

6 healthy adult male domestic pigeons.

PROCEDURES

During the first of 3 experiments, birds received orally administered trazodone at doses ranging from 3 to 30 mg/kg to determine the dose for subsequent experiments. During the second experiment, each bird received 1 dose of trazodone (30 mg/kg, PO). Blood was collected for determination of plasma trazodone concentration before and at predetermined times for 24 hours after drug administration. Pharmacokinetic parameters were calculated by noncompartmental analysis. During experiment 3, birds were instrumented with ultralightweight accelerometers and received orally administered trazodone (30 mg/kg) or an equal volume of water twice at a 48-hour interval. Activity of birds was monitored for 24 hours after administration of each treatment.

RESULTS

No adverse effects were observed. Mean ± SD terminal half-life of trazodone was 5.65 ± 1.75 hours. Plasma trazodone concentrations remained > 0.130 μg/mL for approximately 20 hours. Trazodone did not affect the activity of birds during the first 2 and 15 hours after administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that oral administration of 1 dose (30 mg/kg) of trazodone to healthy pigeons was safe and resulted in plasma drug concentrations that were similar to those considered therapeutic in humans and dogs for up to 20 hours. Further research is necessary to characterize the pharmacokinetics for repeated doses as well as the clinical effects of trazodone in birds with behavior problems.

Effect of oral trazodone on the minimum alveolar concentration of isoflurane in dogs

OBJECTIVE

To determine the effect of oral trazodone on the minimum alveolar concentration (MAC) of isoflurane in dogs.

STUDY DESIGN

Prospective blinded, single-observer, randomized crossover experimental study.

ANIMALS

Six adult (age 6.8 ± 1.6 months) healthy dogs (three males and three females), weighing 24.8 ± 3.4 kg (mean ± standard deviation).

METHODS

Each dog was anesthetized twice with a minimum of 7 days between anesthetic episodes. Dogs were randomly assigned to be administered two treatments in a crossover design: premedication with trazodone (8 mg kg^-1; TRAZ-ISO) orally 2 hours prior to an anesthetic episode or no (ISO). Dogs were anesthetized with intravenous propofol (6 mg kg^-1) and isoflurane in >95% oxygen. Isoflurane MAC was determined using an iterative bracketing technique with electrodes placed in the buccal mucosa. Hemodynamic variables were compared at the lowest end-tidal isoflurane concentration at which each dog did not respond. A paired t test was used to assess the effect of treatment on outcome variables with significance set to a value of p < 0.05.

RESULTS

The MAC concentration (mean ± standard deviation) in dogs administered TRAZ-ISO was 0.85 ± 0.17% compared with 1.02 ± 0.11% in those administered ISO (p = 0.01, 95% confidence interval -0.25 to -0.05), resulting in a mean MAC reduction of 17 ± 12%. There were no differences in hemodynamic variables between treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Premedication of dogs with oral trazodone (8 mg kg^-1) 2 hours prior to anesthetic induction has a significant isoflurane MAC sparing effect with no significant observed hemodynamic benefit.