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

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.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in cats

Objective

To determine if oral gabapentin decreases the minimum alveolar concentration (MAC) of isoflurane in cats.

Study design

Prospective, randomized, blinded, crossover, and experimental study.

Animals

A total of six healthy adult cats (three male, three female) aged 18-42 months, weighing 3.31 ± 0.26 kg.

Methods

Cats were randomly given oral gabapentin (100 mg cat^-1) or placebo 2 h before starting MAC determination, with the crossover treatment given at least 7 days apart. Anesthesia was induced and maintained with isoflurane in oxygen. Isoflurane MAC was determined in duplicate using an iterative bracketing technique and tail clamp method. Hemodynamic and other vital variables were recorded at each stable isoflurane concentration and were compared between gabapentin and placebo treatments at lowest end-tidal isoflurane concentration when cats did not respond to tail clamping. A paired t-test was used to compare normally distributed data, and a Wilcoxon signed-rank test was applied for non-normally distributed data. Significance was set at p < 0.05. Data are mean ± standard deviation.

Results

Isoflurane MAC in the gabapentin treatment was 1.02 ± 0.11%, which was significantly lower than that in the placebo treatment (1.49 ± 0.12%; p < 0.001), decreasing by 31.58 ± 6.94%. No significant differences were found in cardiovascular and other vital variables between treatments.

Conclusion and clinical relevance

Oral administration of gabapentin 2 h before starting MAC determination had a significant isoflurane MAC-sparing effect in cats with no observed hemodynamic benefit.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in dogs

OBJECTIVE

To determine the effect of oral administration of gabapentin (20 mg/kg) on the minimum alveolar concentration (MAC) of isoflurane in dogs.

ANIMALS

6 healthy adult dogs (3 males and 3 females with a mean ± SD body weight of 24.8 ± 1.3 kg).

PROCEDURES

Each dog was anesthetized twice. Dogs were initially assigned to 1 of 2 treatments (gabapentin [20 mg/kg, PO] followed 2 hours later by anesthesia maintained with isoflurane or anesthesia maintained with isoflurane alone). A minimum of 7 days later, dogs received the other treatment. The MAC of isoflurane was determined by use of an iterative bracketing technique with stimulating electrodes placed in the maxillary buccal mucosa. Hemodynamic variables and vital parameters were recorded at the lowest end-tidal isoflurane concentration at which dogs did not respond to the stimulus. Effect of treatment on outcome variables was analyzed by use of a paired t test.

RESULTS

Mean ± SD MAC of isoflurane was significantly lower when dogs received gabapentin and isoflurane (0.71 ± 0.12%) than when dogs received isoflurane alone (0.91 ± 0.26%). Mean reduction in MAC of isoflurane was 20 ± 14%. Hemodynamic variables did not differ significantly between treatments. Mean time to extubation was significantly less when dogs received gabapentin and isoflurane (6 ± 4 minutes) than when dogs received isoflurane alone (23 ± 15 minutes).

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of gabapentin 2 hours before anesthesia maintained with isoflurane had a MAC-sparing effect with no effect on hemodynamic variables or vital parameters of dogs.