Effects of orally administered gabapentin, tramadol, and meloxicam on ocular variables in healthy dogs

Effects of gabapentin on intraocular pressure, tear production and horizontal pupil diameter in New Zealand White rabbits

BACKGROUND

This study aimed to investigate the effects of gabapentin on various ocular parameters in New Zealand White rabbits.

METHODS

A randomised, placebo-controlled crossover study design was employed. Eight New Zealand White rabbits were randomly assigned to receive either oral gabapentin at a dosage of 15 mg/kg or an oral placebo, with a 1-week washout period between treatments. Intraocular pressure, tear production and horizontal pupil diameter were measured at baseline (T0) and at 30, 60, 90, 120, 180, 240 and 360 minutes after drug administration. Physiological and behavioural changes were also recorded for both treatments following drug administration.

RESULTS

The administration of gabapentin did not have any significant effects on the ocular parameters measured in this study. However, the rabbits exhibited some muscle relaxation with partially closed eyes during handling, and they were slightly easier to remove from the cage when treated with gabapentin compared to the placebo treatment.

LIMITATIONS

In this study, the ocular effects of gabapentin were assessed in only a small number of healthy rabbits. These effects may differ in rabbits with pre-existing eye conditions or in those receiving other medications.

CONCLUSIONS

Our findings suggest that gabapentin treatment does not have a significant impact on intraocular pressure, tear production or horizontal pupil diameter in rabbits.

Gabapentin: Clinical Use and Pharmacokinetics in Dogs, Cats, and Horses

Gabapentin is an anticonvulsant drug, which presents an established clinical efficacy in human patients for the management of refractory partial seizures, secondarily generalized tonic-clonic seizures, and for the control of chronic neuropathic pain. Gabapentin was synthesized as a structural analogue of the inhibitory neurotransmitter GABA, with GABA-mimetic effects, able to cross the blood-brain barrier. In veterinary medicine, is extra-label used in combination with other treatments to control seizures when other drugs are no longer effective or become toxic or for neuropathic pain treatment and anxiety. This review aimed to clarify gabapentin use and pharmacokinetic aspects to promote conscious use in dogs, cats, and horses. In dogs, gabapentin was beneficial in the treatment of epilepsy, as well as chronic, neuropathic, and post-operative pain, as well as anxiety. In cats, it showed efficacy in post-ovariohysterectomy-related pain and in anxiety management. In horses, gabapentin has been administered as an analgesic for chronic pain management. In conclusion, when used in combination with other drugs, gabapentin can be considered an interesting therapeutic option for the treatment of neuropathic diseases and analgesia in postoperative and chronic pain. However, despite its beneficial use in different clinical settings, further trials and pharmacokinetic studies are needed for the definition of an effective dosage regimen through proper pharmacokinetic/pharmacodynamic correlation in dogs, cats, and horses.

Diagnostic Tests Used During the Ocular Examination

This article provides a review of the required ocular tests during the ophthalmologic examinations of canine and feline patients. Knowledge of medications affecting ocular parameters and awareness of available instrumentation and test materials is essential for accurate diagnoses.

Comparison of three rebound tonometers in normal and glaucomatous dogs

OBJECTIVE

The objectives of the study were to compare intraocular pressure (IOP) readings across a wide range and obtained via three rebound tonometers in ADAMTS10-mutant Beagle-derived dogs with different stages of open-angle glaucoma (OAG) and normal control dogs and to investigate the effect of central corneal thickness (CCT).

ANIMALS STUDIED

Measurements were performed on 99 eyes from 50 Beagle-derived dogs with variable genetics-16 non-glaucomatous and 34 with ADAMTS10-OAG. Seventeen OAG eyes were measured twice-with and without the use of IOP-lowering medications.

PROCEDURES

IOP was measured in each eye using three tonometers with their "dog" setting-ICare® Tonovet (TV), ICare® Tonovet Plus® (TVP), and the novel Reichert® Tono-Vera® Vet (TVA)-in randomized order. CCT was measured with the Accutome® PachPen. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and regression analyses of tonometer readings and pairwise IOP-CCT Pearson correlations (MiniTab®).

RESULTS

A total of 116 IOP measurements were taken with each of the three tonometers. When comparing readings over a range of ~7-77 mmHg, mean IOPs from the TV were significantly lower compared with TVP (-4.6 mmHg, p < .001) and TVA (-3.7 mmHg, p = .001). We found no significant differences between TVA and TVP measurements (p = .695). There was a moderate positive correlation between CCT and IOP for TVA (r = 0.53, p < .001), TVP (r = 0.48, p < .001), and TV (r = 0.47, p < .001).

CONCLUSIONS

Our data demonstrate strong agreement between TVP and TVA, suggesting that the TVA may similarly reflect true IOP values in canines. CCT influenced IOP measurements of all three tonometers.

Behavioral and cardiovascular effects of a single dose of gabapentin or melatonin in cats: a randomized, double-blind, placebo-controlled trial

OBJECTIVES

The aim of this study was to verify whether a single oral dose of gabapentin (100 mg) or melatonin (3 mg) given 60 mins before a cardiac evaluation would reduce anxiety without interfering with heart rate (HR), systemic blood pressure (SBP), electrocardiogram (ECG) and echocardiographic indexes.

METHODS

Seventy-five client-owned healthy cats underwent two sets of cardiac assessments 60 mins apart, randomly divided into gabapentin, melatonin and placebo groups. The interval between treatment and the second ECG and SBP measurement was 60 mins, and 70 mins for echocardiography. A compliance score (CS) classified the behavior, focusing on the ease of handling.

RESULTS

Most variables did not change between the examinations. The placebo group showed more significant changes (SBP, tricuspid annular plane systolic excursion, HR during echocardiography, aortic flow velocity, S' wave from lateral mitral annulus), but they were not considered to be hemodynamically relevant. Gabapentin and melatonin significantly increased the cats' compliance without interfering with cardiac assessment. Eight cats presented with mild sedation, seven after gabapentin and one after melatonin. No major side effects were observed.

CONCLUSIONS AND RELEVANCE

Gabapentin tranquilized the cats when it was given 60 mins prior to ECG and SBP measurement, and 70 mins prior to echocardiography, without interfering with systolic echocardiographic indexes. Melatonin also decreased the CS, but without sedation in most cases. The waiting period may have relaxed the cats in the placebo group, resulting in lower SBP measurements. However, this tranquility did not last as some echocardiographic changes signaled a sympathetic predominance.

Gabapentin reduces stress and does not affect ocular parameters in clinically normal cats

OBJECTIVE

To describe the effects of gabapentin on ocular and behavioral parameters following oral administration in healthy cats.

MATERIALS AND METHODS

Masked, placebo-controlled, randomized crossover-design study. Ten young, healthy cats were scheduled for two veterinary visits 7 days apart and randomly assigned to receive a compounded capsule containing 100 mg of gabapentin or placebo (100 mg lactose powder) at the first visit and the opposite treatment at the second visit. Respiratory rate, heart rate, stress score, sedation score, compliance score, horizontal pupil diameter, intraocular pressure, and Schirmer tear test-1 were measured prior to and 1.5, 3, and 6 h following capsule administration. Stress score, sedation score, and compliance score were assigned based on established behavioral scales. Results of the two treatments were statistically compared with a p-value <0.05 considered significant.

RESULTS

Respiratory rate was significantly reduced at 1.5 (p = 0.049) and 3 (p = 0.03) hours following gabapentin administration. Stress score was significantly reduced at 1.5 (p = 0.01) hours following gabapentin administration. Sedation score was significantly increased at 1.5 (p = 0.015) and 3 (p = 0.03) hours following gabapentin administration. Gabapentin had no significant effect on heart rate, compliance score, or ocular values measured in this study.

CONCLUSIONS

Gabapentin reduces stress and increases sedation at 1.5 h after treatment, with no significant effect on horizontal pupil diameter, intraocular pressure or Schirmer tear test-1 results.

Investigation of fluorescein stain-based tear film breakup time test reliability in dogs in a clinical setting

OBJECTIVE

To determine intra- and interobserver reliability of a fluorescein stain-based tear film breakup time (TFBUT) test as performed in a clinical environment with and without administration of a topical anesthetic.

ANIMALS

21 privately owned dogs.

PROCEDURES

A randomized study design was used. Two independent observers that commonly perform the TFBUT test in clinical practice read the same description of TFBUT. Observers performed TFBUT testing for each dog before and after topical administration of 0.5% proparacaine solution in 4 testing periods with a 1-hour interval between periods. Intraclass correlation coefficient (ICC) analysis was used to assess inter- and intraobserver test reliability. Linear mixed models were used to assess the main effects of testing period, observer, eye, and presence of ophthalmic disorders and their interactions on TFBUT.

RESULTS

Mean TFBUT measurements performed by observer 1 and observer 2 were 5.9 seconds and 8.6 seconds, respectively, when adjusted for other effects in the model. Intraobserver ICC was poor for one observer and moderate for the other. Interobserver ICC was poor without use of topical anesthetic and slightly lower when anesthetic was used. Observer and testing period were each significantly associated with TFBUT; the measurements decreased and were more variable after multiple applications of fluorescein stain and proparacaine.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested tear film stability is negatively affected by topical administration of 0.5% proparacaine solution and repeated applications of fluorescein stain. The TFBUT test as performed in this study had poor to moderate reliability.