Effects of premedication with oral gabapentin on intraocular pressure changes following tracheal intubation in clinically normal 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.

Intraocular pressure and cardiovascular effects of dexmedetomidine premedication and tiletamine-zolazepam for anesthetic induction in dogs

Background and Aim

The effect of anesthetic drugs on intraocular pressure (IOP) is an important concern in ophthalmic surgery. The impact of dexmedetomidine (DEX) combined with tiletamine-zolazepam on IOP is scarcely studied. This study aimed to evaluate IOP and cardiovascular effects in dogs after premedication with 5 μg/kg (DEX5) or 10 μg/kg (DEX10) of intramuscular DEX followed by intravenous tiletamine-zolazepam administration for induction of anesthesia in healthy dogs.

Materials and Methods

Eighteen dogs, American Society of Anesthesiologists I or II, without ocular abnormality were investigated. All dogs were randomly divided into the DEX5 (n = 9) and DEX10 groups (n = 9). The IOP, heart rate (HR), systolic blood pressure (SBP), oxygen saturation, and sedation scale were measured before premedication (baseline), after premedication at 5, 10, 15, and 20 min, after tiletamine-zolazepam administration, after endotracheal intubation, and post-operative.

Results

There were no significant differences between the groups at any time point. The DEX5 and DEX10 groups had significantly decreased HR values at 10 min compared with baseline. The IOP at 20 min was significantly lower compared to the baseline in the DEX10 group. Moreover, the DEX10 group showed increased IOP, HR, SBP, and sedation scale values after induction and intubation compared with 20 min, but these values did not differ significantly from baseline. All parameters of both groups did not change significantly between post-operative and baseline.

Conclusion

Intramuscular DEX (10 μg/kg) is an appropriate premedication in ophthalmic examination or surgical procedures. Moreover, it could be combined with tiletamine-zolazepam for generalized anesthesia in dogs with an ophthalmic problem, as it had no clinically significant effects on IOP or cardiovascular values.

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.

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

OBJECTIVE

To determine the effects of gabapentin, tramadol, and meloxicam on tear production, intraocular pressure (IOP), pupillary diameter, tear break-up time, and corneal touch threshold in healthy dogs when given orally for 3 days.

ANIMALS

9 healthy research Beagles.

PROCEDURES

A randomized, blinded, case-crossover study with a 6-sequence, 3-treatment, and 3-period design was performed. A 7-day acclimation period was followed by 3 treatment phases, each with a 3-day treatment period followed by a 7-day washout period for 3 different drugs. Block randomization was used to group dogs for treatments with drug A (gabapentin), B (tramadol), or C (meloxicam). Measurements of tear production, IOP, pupillary diameter, tear break-up time, and corneal touch threshold were performed on a schedule. A generalized mixed-effects linear regression model was created for each ocular variable, accounting for repeated measures within individuals.

RESULTS

Intraocular pressure was the only variable to have differed substantially between the first 5 and last 2 days of the acclimation period. When treatment phase, day, time of day, dog identification, baseline value, and eye were accounted for, the mean IOP was lower for dogs during treatment phases with gabapentin or tramadol, compared with meloxicam, but this difference was not considered clinically meaningful.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a minimum 5-day acclimation period is necessary for IOP measurements to return to baseline in dogs. The statistically identified effect of gabapentin and tramadol on IOP in dogs of the present study warrants further investigation. It is possible that at higher dosages, or in dogs with glaucoma, this effect may become clinically significant.