Effect of topical 0.03% flurbiprofen and 0.005% latanoprost, alone and in combination, on normal canine eyes

Effects of topical ketorolac tromethamine on tear parameters, meibography, goblet cell density, and conjunctival oxidative stress in healthy dogs

OBJECTIVES

The objective of the study was to evaluate whether a twice-daily instillation of 0.45% preservative-free ketorolac tromethamine (FKT) or 0.4% benzalkonium chloride-preserved ketorolac tromethamine (BACKT), every 12 h for 30 days may affect tear film parameters and the meibography in healthy dogs. Additionally, we assessed whether the same treatments irritated the ocular surface, affected goblet cell density (GCD), and the levels of oxidative stress biomarkers (OSB) in the conjunctiva of the same dogs.

PROCEDURES

Experimental and masked comparison study. In 11 healthy dogs baseline values of the lipid layer thickness, tear meniscus height, non-invasive tear breakup time (NI-TFBT), and the meibomian gland (MG) loss were assessed by OSAvet®. For each dog, one eye received 40 μL of BACKT, while the other received 40 μL FKT, every 12 h for 30 consecutive days. Tear parameters and meibography were repeated 15, 30, and 60 days post-treatments. Conjunctival hyperemia and blepharospasm were monitored at the same time points. At baseline and Day 30, a conjunctival biopsy was collected for GCD and OSB determination.

RESULTS

Conjunctival hyperemia and blepharospasm were not observed. At Day 15, the MG loss increased only in FKT-treated eyes (p < .001). On Day 30, both treatment groups showed increased MG loss, shortened NI-TFBT, and reduced GCD and catalase (p < .05). At Day 30, BACKT-treated eyes showed lower levels of superoxide dismutase (SOD) (p = .006) and higher levels of malondialdehyde (MDA) (p = .02). Differences between treatments were not observed for any parameter at any time point (p > .05). 60 days after treatment, OSAvet® parameters tended to return to values assessed at baseline; however, significant differences remained for MG loss (p < .05).

CONCLUSIONS

Twice-daily instillation of KT, containing or not BAC, for 30 consecutive days shortened NI-TFBT, decreased GCD, and increased the MG loss in healthy dogs. KT should be used with caution when prescribed for long periods, particularly in patients with tear film abnormalities. However, future controlled studies using KT, BAC, and other topical NSAIDs are indicated to further support this finding.

Role of Inflammation in Canine Primary Glaucoma

Primary glaucoma is a painful, progressive, and blinding disease reported in many canine breeds, characterized by intraocular pressure (IOP) elevation in the absence of antecedent intraocular disease. Clinical observations of dogs with primary glaucoma suggest that many affected eyes develop concurrent intraocular inflammation in addition to elevated IOP. In this work, we summarize the current knowledge that relates inflammation to primary glaucoma in dogs, reviewing studies focused on genetics, physiology, histopathology, bioanalysis of ocular fluids, therapeutics, and clinical outcomes of glaucomatous patients. Through disruption of the blood-aqueous and blood-retinal barriers, pigment dispersion, and biochemical changes to the aqueous humor and tear film, the pathogenesis of canine primary glaucoma appears to involve inflammatory changes to various extents and with various consequences from the front to the back of the eye. Among others, inflammation further impacts IOP by reducing aqueous humor outflow at the level of the iridocorneal angle and accelerates vision loss by promoting neuronal degeneration. As such, the vicious cycle of ocular inflammation and IOP elevation might warrant the use of anti-inflammatory medications as a core component of the treatment regime for dogs with primary glaucoma, either therapeutically (i.e., actively glaucomatous eye) or prophylactically in the yet unaffected contralateral eye.

Topical Ocular Therapeutics in Small Animals

This article reviews the administration of common topical ophthalmic medications, in relation to factors influencing absorption including composition of topical ophthalmic preparations, and potential systemic effects. Commonly prescribed, commercially available topical ophthalmic medications are discussed with respect to pharmacology, their indications for use, and adverse effects. Knowledge of topical ocular pharmacokinetics is essential for the management of veterinary ophthalmic disease.

Comparative effects of latanoprost and latanoprostene bunod on intraocular pressure and pupil size in ophthalmologically normal Beagle dogs

OBJECTIVE

To compare effects of latanoprost, a topical prostaglandin analogue (PGA) commonly used to treat glaucoma and lens instability in dogs, and latanoprostene bunod, a novel PGA with a nitric oxide-donating moiety, on intraocular pressure (IOP) and pupil diameter (PD).

ANIMALS STUDIED

Ten ophthalmologically normal Beagle dogs.

PROCEDURES

Dogs were treated twice a day for 5 days in a randomly selected eye with either latanoprost or latanoprostene bunod. After a 6-week washout period, dogs were treated with the opposite drug. IOP and PD were measured at treatment times, at midday on days 1 and 5, and for 6 days post-treatment.

RESULTS

Both drugs significantly decreased IOP and PD. At midday on day 5 of treatment, mean IOP in eyes treated with latanoprost was 4.5 mmHg lower than the fellow eye and 3.0 mmHg lower than the same eye at baseline, while mean IOP in eyes treated with latanoprostene bunod was 5.5 mmHg lower than the fellow eye and 3.6 mmHg lower than baseline. Mean PD was 0.94 mm in eyes treated with latanoprost and 0.76 mmHg in eyes treated with latanoprostene bunod. There was no significant difference between the two drugs for either parameter at that time point (p = .372 and .619, respectively, for IOP relative to control and to baseline; p = .076 for PD) or when analyzed longitudinally. Significant diurnal variation in PD was noted and may have implications for treatment of lens' instability.

CONCLUSIONS

Latanoprost and latanoprostene bunod produce similar IOP reduction and miosis in normal canine eyes.

Intraocular Pressure-Lowering Efficacy of a Sustained-Release Bimatoprost Implant in Dog Eyes Pretreated with Selective Laser Trabeculoplasty

Purpose: To assess the intraocular pressure (IOP)-lowering effect of a biodegradable bimatoprost implant following selective laser trabeculoplasty (SLT) in a canine model. Methods: Unilateral SLT was performed in 11 normotensive, treatment-naive beagle dogs. IOP was measured at baseline (pre-SLT) and weekly post-SLT (≤10 weeks). After IOP returned to baseline or at 10 weeks (whichever occurred first), a sustained-release bimatoprost implant was administered bilaterally in the anterior chamber of each animal. IOP was measured weekly for 4 weeks and then every 2 weeks up to week 42. Results: The main outcomes included the IOP change (%) from baseline, calculated in both eyes in the overall population, SLT responder subgroup (defined by peak IOP reduction from baseline ≥3 mmHg or ≥15% for >1 week post-SLT), and SLT nonresponder subgroup (defined by peak IOP reduction from baseline <3 mmHg or <15%). The bimatoprost implant lowered IOP similarly in both the SLT-treated and fellow SLT-naive eyes. Following bimatoprost implant administration, the mean (standard deviation [SD]) peak IOP reduction from baseline was 34.4% (8.5%) in SLT-treated eyes and 35.7% (5.9%) in fellow SLT-naive eyes. The bimatoprost implant lowered IOP comparably (P > 0.17) in eyes that responded to SLT (mean [SD] peak IOP reduction, 34.6% [10.7%]; n = 6) and those that did not (mean [SD] peak IOP reduction, 34.1% [6.1%]; n = 5). Conclusion: The bimatoprost implant effectively lowered IOP in eyes pretreated with SLT, regardless of response to SLT. The current data suggest that eyes previously treated with SLT can still benefit from the intracameral bimatoprost implant.

The association of topical flurbiprofen with the incidence of postoperative glaucoma after phacoemulsification in dogs

OBJECTIVE

To investigate the relationship between topical administration of flurbiprofen plus corticosteroids versus corticosteroids alone following phacoemulsification and the development of postoperative glaucoma in dogs.

ANIMAL STUDIED

Thirty-eight/eighty-three (45.8%) eyes were prescribed topical flurbiprofen plus corticosteroids immediately postop while 45/83 (54.2%) eyes received topical corticosteroids alone.

PROCEDURES

Logistic regression models were performed to analyze the relationship between topical flurbiprofen and development of glaucoma and to predict potential risk factors for postoperative glaucoma occurrence.

RESULTS

Eighty-three eyes (65 dogs) were included. The mean age at surgery was 8.2 years, with even gender distribution. Increasing age at the time of surgery significantly increased the probability of postoperative glaucoma occurrence (odds ratio [OR] = 1.344, 95% confidence interval [CI] 1.093-1.652; p = 0.005). Glaucoma occurred in 17/83 (20.5%) eyes; of these, 15/38 (39.5%) and 2/45 (4.4%) eyes were prescribed topical flurbiprofen plus corticosteroids and topical corticosteroids alone, respectively. Immediate postoperative use of topical flurbiprofen was significantly associated with an increased probability of postoperative glaucoma occurrence (OR = 19.183 [95% CI 3.367-109.286], p = 0.001).

CONCLUSIONS

Immediate postoperative use of topical flurbiprofen was a potential predisposing risk factor for the development of glaucoma following phacoemulsification. Restriction of postoperative use of topical flurbiprofen might decrease the possibility of postoperative glaucoma development in dogs.

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.

Effect of topical administration of 0.1% diclofenac sodium ophthalmic solution at four frequencies on intraocular pressure in healthy Beagles

OBJECTIVE

To evaluate effects of topical ophthalmic administration of diclofenac on intraocular pressure (IOP) when applied at 4 frequencies to eyes of Beagles.

ANIMALS

8 ophthalmologically normal Beagles.

PROCEDURES

The study involved four 5-day experimental periods each separated by a 16-day washout period. During each period, 1 drop of 0.1% diclofenac sodium ophthalmic solution was administered to the right eye at 4 treatment frequencies (1, 2, 3, or 4 times/d); 1 drop of eyewash was administered to the left eye as a control treatment. A complete ophthalmic examination was performed on days 0 (day before first treatment) and 5 of each experimental period. Gonioscopy was performed on day 0 of the first period. The IOPs were measured at 7 am and 7 pm on days 1 through 5.

RESULTS

No abnormalities were detected during neuro-ophthalmic and ophthalmic examinations on day 0 of each experimental period. No adverse reactions to administration of diclofenac or eyewash were observed at any time point. No abnormalities were detected during ophthalmic examinations performed on day 5, and IOPs remained < 25 mm Hg in all 4 periods. No significant differences were identified between the treated and control eyes or among the 4 treatment frequencies.

CONCLUSIONS AND CLINICAL RELEVANCE

Topical ophthalmic administration of diclofenac up to 4 times/d in dogs with no ophthalmic abnormalities did not significantly increase the IOP. Additional research is needed to evaluate the effect of topical ophthalmic administration of diclofenac on IOP in dogs with anterior uveitis.

Albumin Levels in Tear Film Modulate the Bioavailability of Medically-Relevant Topical Drugs

The breakdown of blood-tear barrier that occurs with ocular pathology allows for large amounts of albumin to leak into the tear fluid. This process likely represents an important restriction to drug absorption in ophthalmology, as only the unbound drug is transported across the ocular tissue barriers to exert its pharmacologic effect. We aimed to investigate the effects of albumin levels in tears on the bioavailability of two commonly used ophthalmic drugs: tropicamide, an antimuscarinic that produces mydriasis and cycloplegia, and latanoprost, a PGF2α analog used for the treatment of glaucoma. Eight female beagle dogs underwent a randomized, vehicle-controlled crossover trial. For each dog, one eye received 30 µl of artificial tears (control) or canine albumin (0.4 or 1.5%) at random, immediately followed by 30 µl of 1% tropicamide (2 days, 24 h washout) or 0.005% latanoprost (2 days, 72 h washout) in both eyes. Pupil diameter (digital caliper) and intraocular pressure (IOP; rebound tonometry) were recorded at various times following drug administration (0 to 480 min) and compared between both groups with a mixed model for repeated measures. Albumin in tears had a significant impact on pupillary diameter for both tropicamide (P ≤ 0.001) and latanoprost (P ≤ 0.047), with no differences noted between 0.4% and 1.5% concentrations. Reduction in the maximal effect (pupil size) and overall drug exposure (area under the effect time-curve of pupil size over time) were significant for tropicamide (6.2–8.5% on average, P ≤ 0.006) but not for latanoprost (P ≥ 0.663). The IOP, only measured in eyes receiving latanoprost, was not significantly impacted by the addition of either 0.4% (P = 0.242) or 1.5% albumin (P = 0.879). Albumin in tear film, previously shown to leak from the conjunctival vasculature in diseased eyes, may bind to topically administered drugs and reduces their intraocular penetration and bioavailability. Further investigations in clinical patients and other commonly used ophthalmic medications are warranted.

Treatment of canine postoperative ocular hypertension with combined latanoprost 0.005% and atropine 1% ophthalmic solutions

OBJECTIVE

To compare the effects of topical 0.005% latanoprost (L) vs combined 0.005% latanoprost and 1% atropine (LA) on control of postoperative ocular hypertension (POH), development of posterior synechiae formation, pupil size, and blindness after phacoemulsification surgery in dogs.

ANIMAL STUDIED

Dogs with postoperative ocular hypertension were included in the study: L-group, latanoprost (eight dogs, 14 eyes) and LA-group, latanoprost and atropine (nine dogs, 15 eyes).

PROCEDURES

Complete ophthalmic examinations including tonometry were performed at 1, 7, and 21 days following phacoemulsification.

RESULTS

No significant differences were found between the measured intraocular pressure (IOP) at days 1 and 7 postphacoemulsification surgery in the L-group and the LA-group (P = 0.26 [14.12 ± 1.76 mmHg vs 16.96 ± 1.68 mmHg] and P = 0.71 [15.45 ± 1.43 mmHg vs 16.20 ± 1.36 mmHg], respectively). No significant differences were found between pupil sizes at day 7 for the two groups (P = 0.25 [13.83% vs 24.77%]). No significant differences were found between odds of posterior synechiae formation at day 21 (P = 0.92) with a probability ± SE for L-group vs LA-group at 0.27 ± 0.14 vs 0.25 ± 0.13. No significant differences were found in odds of postoperative blindness between groups (P = 0.58) with a probability ± SE of 0.21 ± 0.11 vs 0.13 ± 0.09, respectively for L and LA.

CONCLUSIONS

Combined topical latanoprost and atropine in dogs maintains normal postoperative IOPs but does not seem to cause increased mydriasis compared to latanoprost alone.

Glaucomas

Canine and feline glaucomas are commonly presented as ocular emergencies. Glaucoma is a common cause of vision loss and a frustrating disorder in terms of medical and surgical treatment. Increased intraocular pressure (IOP) is a significant risk factor in the disease, leading to damage of the retina and optic nerve head. IOP measurement and gonioscopic and fundic examinations provide the instruments for diagnosis of glaucoma. The primary goal in glaucoma therapy is aimed at vision preservation. Medical treatment provides temporary relief, but alone it fails to control IOP in the long term, and surgical intervention is recommended. Surgical patient selection depends on several factors, from type and stage of glaucoma to the presence of or potential for vision. Available surgical procedures to decrease IOP consist of cyclodestructive techniques to decrease aqueous humor production and filtering techniques to increase its drainage. Even with recent surgical and medical advances, pain and blindness are still common occurrences in the disease: end-stage procedures such as enucleation, evisceration with intrascleral prosthesis, and pharmacologic ablation of ciliary bodies are then recommended to address chronic discomfort for buphthalmic and blind globes.