Ocular absorption, blood levels, and excretion of dorzolamide, a topically active carbonic anhydrase inhibitor

Risks of Topical Carbonic Anhydrase Inhibitors in Glaucoma Patients With Chronic Kidney Disease: A Nationwide Population-Based Study

PURPOSE

To investigate the risks of metabolic acidosis and renal outcomes after topical carbonic anhydrase inhibitor (CAI) use in patients with both primary open-angle glaucoma (POAG) and advanced chronic kidney disease (CKD).

DESIGN

Nationwide, population-based cohort study.

METHODS

This study was conducted with population data from Taiwan's National Health Insurance (NHI) Research Database between January 2000 and June 2009. Patients with advanced CKD who were diagnosed with glaucoma (International Classification of Diseases, Ninth Revision [ICD-9] code 365) and had been receiving eye drops for glaucoma (including carbonic anhydrase inhibitors selected by NHI drug code) were enrolled. Using Kaplan-Meier methods, we compared the cumulative incidence of mortality, long-term dialysis, and cumulative incidence of metabolic acidosis over time between CAI users and CAI non-users. Primary outcomes comprised mortality, renal outcome (progression to hemodialysis), and metabolic acidosis.

RESULTS

In this cohort, topical CAI users had a higher incidence of long-term dialysis than non-users (incidence = 1,216.85 vs 764.17 events per 100 patient-years; adjusted hazard ratio = 1.17, 95% CI = 1.01-1.37). Hospital admissions due to metabolic acidosis were higher in CAI users compared with non-users (incidence = 21.54 vs 11.87 events per 100 patient-years; adjusted hazard ratio = 1.89, 95% CI = 1.07-3.36).

CONCLUSIONS

Topical CAIs may be associated with higher risks of long-term dialysis and metabolic acidosis in patients with POAG and pre-dialysis advanced CKD. Therefore, topical CAIs should be used with caution in advanced CKD patients.

Adverse analytical finding due to red blood cells transfusion: A rare case involving the diuretic dorzolamide

Early November 2020 an Olympic gold medal winner returned during an out-competition control an adverse analytical finding for dorzolamide, a diuretic mostly used to treat glaucoma. Estimated urine concentrations were 2.2 and 1.6 ng/ml in the A and B specimens, respectively. As the athlete denied any use of dorzolamide, a complex forensic investigation was suggested. It revealed that the athlete was severely injured during a car crash 6 months before where he received 2× 500 ml of red blood cells transfusion. One of the blood donors declared using dorzolamide. A plasma aliquot, stored for legal purposes, was tested by LC-MS/MS several months later and contained 4.3 ng/ml of dorzolamide. Given the very long half-life of the drug, up to 150 days and its reported incorporation into erythrocyte, it was accepted by the French antidoping administration (AFLD) that the source of contamination was this blood transfusion and that the antidoping rule violation was unintended.

Cases reports: Unintended anti-doping rule violation after dorzolamide use several months prior to a doping control

The use of specific medicine up to several months before a doping control is not be reported on the doping control form, while the drug could then still be detectable in urine in case of a very slow elimination. It may lead to a positive test result. For example, dorzolamide, a carbonic anhydrase inhibitor for topical ophthalmic application, has a very slow elimination rate via the renal route (half-life > 4 months). This substance can be a source of unintended anti-doping rule violations.

Increased ratios of complement factors C3a to C3 in aqueous humor and serum mark glaucoma progression

INTRODUCTION

We recently performed a combined analysis of publicly available proteomic studies of aqueous humor (AH) of patients with primary open angle glaucoma (POAG). This analysis revealed changes in complement protein concentrations in the AH of progressive POAG patients, which suggested that the complement system may play a role in POAG progression. As the proteomic studies could not provide information on the activity of the complement system, we addressed this question in the current study.

METHODS

Blood serum and AH were obtained from 30 patients: 10 progressive POAG, 10 stable POAG and, as controls, 10 cataract patients. Glaucoma patients with a visual field Mean Deviation (MD) change of at least 1.0 dB/year were considered progressive; a MD change of less than 0.5 dB/year was considered stable. The ratio between the levels of complement factors C3a and C3 was used as indicator for activation of the complement cascade. The factors were measured with commercially available ELISA kits.

RESULTS

AH levels of complement factors C3 and C3a did not significantly differ between groups. In serum, complement factor C3 did not differ between groups whereas C3a was significantly elevated in progressive POAG patients compared to controls (p < 0.05). The resulting complement C3a/C3 ratio was significantly higher in progressive POAG patients in both AH (p < 0.05) and serum (p < 0.01), and this ratio significantly correlated between the two body fluids (p < 0.001). Furthermore, there was a strong correlation between disease progression and C3a/C3 activation ratio both in AH (p < 0.01) and in serum (p < 0.001). The higher the complement C3a/C3 ratio, the faster the disease progression.

CONCLUSION

Significant increases in AH and serum complement C3a/C3 ratios were observed in progressive POAG patients but not in stable POAG patients. Furthermore, the complement C3a/C3 ratio correlated strongly with the rate of disease progression in both AH and serum. These findings suggest that activation of the complement system plays a role in glaucoma progression and that progressive glaucoma patients may have systemic changes in complement activation.

Hypokalemia associated with topical administration of dorzolamide 2% ophthalmic solution in cats

OBJECTIVE

To evaluate the effect of dorzolamide 2% ophthalmic solution on serum potassium and other hematologic parameters in cats.

MATERIALS AND METHODS

Part I: Medical records from a single institution were retrospectively reviewed. Inclusion criteria consisted of cats diagnosed with glaucoma for which appropriate clinicopathological data were available both prior to and after the initiation of therapy with dorzolamide 2% ophthalmic solution. Part II: Healthy adult cats were enrolled in a prospective double-masked, randomized, cross-over study. Either dorzolamide 2% ophthalmic solution or placebo was administered OU t.i.d. for 6 weeks. Serum potassium, sodium, chloride, glucose, ALP, and ALT levels were assessed every 2 weeks. After a 2-week washout period, each cat was given the opposite topical preparation, and the study process was repeated.

RESULTS

Part I: Of the twenty-seven eligible cases, hypokalemia developed in 29.6% (n = 8). While female spayed cats were significantly more likely to become hypokalemic, serum potassium was not significantly affected by age, weight, dosing frequency, or number of eyes treated. Part II: Ten cats participated in the study. Potassium values were significantly lower in cats receiving dorzolamide 2% ophthalmic solution compared to placebo at each time point throughout the 6-week study period. Additionally, chloride values were significantly greater in the treatment group at week two and four compared to the placebo group.

CONCLUSIONS

Administration of dorzolamide 2% ophthalmic solution has a measurable effect on serum potassium level in cats and may result in clinical hypokalemia. Therefore, routine electrolyte monitoring is advised for feline patients receiving this medication.

The Carbonic Anhydrase Inhibitor Dorzolamide Stimulates the Differentiation of Human Meibomian Gland Epithelial Cells

PURPOSE

Clinical studies have indicated that the long-term use of topical antiglaucoma drugs, such as carbonic anhydrase inhibitors (CAIs), may lead to meibomian gland dysfunction (MGD). We hypothesize that these adverse effects involve a direct influence on human MG epithelial cells (HMGECs). The purpose our present investigation was to test our hypothesis and determine whether exposure to dorzolamide, a CAI, impacts the proliferation, intracellular signaling and differentiation of HMGECs.

MATERIALS AND METHODS

We cultured immortalized (i) HMGECs with vehicle or various concentrations of dorzolamide for 6 days. Cells were enumerated with a hemocytometer, and examined for their morphology, Akt signaling activity, accumulation of neutral lipids, phospholipids and lysosomes, and the expression of protein biomarkers for lipogenesis regulation, lysosomes and autophagosomes.

RESULTS

Our results show that a high, 500 µg/ml concentration of dorzolamide causes a significant decrease in Akt signaling and the proliferation of iHMGECs. However, the high dose of dorzolamide also promotes the differentiation of iHMGECs. This response features increases in the number of lysosomes, the accumulation of phospholipids, and the expression of the light chain 3A biomarker for autophagosomes. In contrast, the therapeutic amount (50 µg/ml) of dorzolamide has no impact on the proliferative or differentiative abilities of iHMGECs.

CONCLUSIONS

Our results support our hypothesis and demonstrate that the CAI dorzolamide does exert a direct influence on the proliferation and differentiation of iHMGECs. However, this effect is elicited only by a high, and not a therapeutic, amount of dorzolamide. Abbreviations: AKT: phosphoinositide 3-kinase-protein kinase B; BPE: bovine pituitary extract; CAD: cationic amphiphilic drug; DED: dry eye disease; DMEM/F12: 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F-12; EGF: epidermal growth factor; FBS: fetal bovine serum; iHMGECs: immortalized human meibomian gland epithelial cells; KSFM: keratinocyte serum-free medium; LAMP-1: lysosomal-associated membrane protein 1; LC3A: light chain 3A; MGD: meibomian gland dysfunction; SREBP-1: sterol regulatory element-binding protein 1.

Pharmacotherapy and Adherence Issues in Treating Elderly Patients with Glaucoma

Glaucoma is a leading cause of visual morbidity throughout the world and is an age-related condition, the prevalence of which rises significantly with increasing age. Glaucoma, a condition affecting the optic nerve, has a variety of subtypes with multiple aetiological factors, the most important of which are intraocular pressure (IOP) and increasing age. Treatment by lowering of IOP is the only current method, for which there is evidence, by which the rate of progressive visual deterioration can be slowed or halted. Although there are surgical and laser treatments that are efficacious in lowering IOP, the most common manner in which patients with glaucoma control their IOP is with administration of daily topical ocular hypotensive drugs (eye drops). The variety of topical drugs utilised in the management of glaucoma all have the potential to have adverse effects and/or interactions with concomitant medications, many of which may be used for other age-related conditions. Adherence with appropriate medicines has a major effect on the outcome of medical conditions and this aspect applies to the management of glaucoma. There are certain specific issues that relate to the administration of topical agents, with respect to both adverse effects and adherence. Although many suspect poor adherence in elderly patients with glaucoma, relative to younger patients, adequate evidence for this is lacking. Furthermore, the manner by which adherence issues could be improved remains inadequately understood and poorly addressed. The aims of this article were to review, from a clinical perspective, the medical therapies currently used for glaucoma and discuss adherence issues with respect to the population of patients with glaucoma, who tend to be relatively elderly.

Safety of carbonic anhydrase inhibitors

INTRODUCTION

Carbonic anhydrase (CA) inhibitors have an impressive safety record despite the multiple functions that CA isozymes serve because they are not fully inhibited with most dosing. While reducing the targeted CA-dependent process sufficiently for disease control, residual activity and uncatalyzed rates in combination with compensations are adequate to avoid lethal consequences. Some drugs have in vitro selectivity differences against the 13 active isozymes, but none are convincingly selective in vivo or clinically. Efforts to synthesize selective inhibitors should result in safer drugs with fewer side effects.

AREAS COVERED

This review will focus on approved drugs with CA-inhibiting activity, whether used directly for this purpose or others. Side effects are discussed in relation to various organ systems and the disease being treated. Causes of side effects are considered, and strategies for symptom reduction are given.

EXPERT OPINION

Common side effects of paresthesias, dyspepsia, lassitude and fatigue in 30 - 40% of patients are generally tolerable or abate, but if not can be partially relieved by bicarbonate supplementation. The most important safety concerns are severe acidosis, respiratory failure and encephalopathy in patients with renal, pulmonary and hepatic disease where caution is critical, as is also the case in persons with sulfa drug allergies.

Effects of antiglaucoma drugs on blood flow of optic nerve heads and related structures

An association between glaucoma development or progression and compromised ocular blood flow has been postulated as a result of population-based studies and prospective cohort studies. Blood flow in the optic nerve head (ONH) is of primary importance in the pathogenesis of glaucoma. The potential to modify the blood flow in the ONH and its related structures has been reported in various agents, including topical antiglaucoma drugs and systemic drugs such as calcium channel antagonists, which are reviewed in this manuscript. Clinical implications of the improvement in ocular blood flow on the treatment of glaucomatous optic neuropathy require further investigation.

The effect of dorzolamide 2% on circadian intraocular pressure in cats with primary congenital glaucoma

OBJECTIVE

To determine the extent of fluctuation in circadian intraocular pressure (IOP) and the efficacy of topical dorzolamide 2% q 8 h in lowering IOP and blunting circadian fluctuation in IOP in glaucomatous cats.

ANIMALS STUDIED

Seven adult cats with primary congenital glaucoma (PCG).

PROCEDURES

Measurements of IOP and pupil diameter were obtained for both eyes (OU) of each cat q 4 h for 12 days. Cats were housed in a laboratory animal facility with a 12-h light:dark cycle. Baseline values were established for 2 days. For the next 5 days, placebo (1.4% polyvinyl alcohol) was administered OU q 8 h. Dorzolamide 2% was then administered OU q 8 h for a further 5 days. A multivariate mixed linear model was fitted to the data, with parameters estimated from a Bayesian perspective. The 4 am time point was selected as the reference for the purposes of comparisons.

RESULTS

Estimated mean IOP for the reference time point pre-treatment was symmetric (about 33 mmHg OU). In all cats, IOP was significantly lower during the diurnal phase, relative to the 4 am measurements, with highest IOP observed 2-6 h after the onset of the dark phase. Circadian fluctuations in IOP were dampened during the treatment period. There was a significant decrease in IOP in all cats during the dorzolamide treatment period (estimated mean for the treatment period reference = 17.9 mmHg OU).

CONCLUSIONS

Topical dorzolamide 2% q 8 h is effective in reducing IOP and IOP fluctuation in cats with PCG.

Efficacy, safety and tolerability of combination therapy with timolol and dorzolamide in glaucoma and ocular hypertension

Combination pharmacotherapy has simplified and improved glaucoma medication regimens. This update focuses on the previous and recent studies on efficacy and tolerability profile of dorzolamide–timolol in adult ocular hypertension and open angle glaucoma patients. Dorzolamide–timolol has been shown to be efficacious and well tolerated in clinical trials and the adverse effects reflect those of the individual components.

Acetazolamide influences ocular pulse amplitude

PURPOSE

To investigate the effect of systemic acetazolamide on ocular pulse amplitude (OPA) and on intraocular pressure (IOP).

METHODS

We determined OPA, IOP, mean arterial blood pressure and heart rate (HR) in 17 patients suffering from hypertensive primary open-angle glaucoma (htPOAG) and 22 healthy controls. Measurements were taken before and 2 h after oral intake of 500 mg of acetazolamide.

RESULTS

Mean OPA decreased 20.24% (SEM 2.95%) from 2.76 mmHg (SEM 0.16 mmHg) to 2.14 mmHg (SEM 0.13 mmHg) 2 h after oral administration of 500-mg acetazolamide. IOP dropped by 2.98 mmHg (SEM 0.28 mmHg), corresponding to a 17.19% (SEM 1.56%) reduction. The decrease in IOP correlated with the decrease of OPA (r(2) = 0.4, P < 0.0001).

CONCLUSIONS

Ocular pulse amplitude measurements are influenced by oral administration of acetazolamide. There was a decrease in the pulsatile component of choroidal blood flow and in IOP in both htPOAG and healthy controls. This needs to be taken into account for measurement of OPA with dynamic contour tonometry.

Local effect of topical FP-receptor agonists on retinal vessels of the ipsilateral posterior retina in normal rabbit eyes

PURPOSE

To determine whether a topically instilled prostaglandin analogue inhibits endothelin-1 (ET-1)-induced vasoconstrictive effects in the posterior retina by its local effects, and the duration of the effect in normal rabbit eyes.

METHODS

Travoprost, a potent selective FP-agonist, or unoprostone, a prostone that also has a weak non-selective FP-agonistic activity, solution was instilled once, or once daily (travoprost) or twice daily (unoprostone) for 7 days in one randomly chosen Dutch rabbit eye, and vehicle in the contralateral eye. ET-1 was intravitreously injected in both eyes 30 min after a single instillation of a test drug or its vehicle, or just after, 30, 60, 90 or 180 min after the final instillation of a 7-day instillation, and fundus photographed before, 30 and 60 min after the injection to study whether difference was seen in the ET-1-induced constriction of retinal vessels between the drug- and vehicle-instilled eyes. The same experimental procedures were conducted with indomethacin pretreatment.

RESULTS

In the rabbit eyes where travoprost was instilled for 7 days, the ET-1-induced constriction of retinal vessels was significantly inhibited only on the drug-treated side, when ET-1 was injected 30 or 60 min after the final instillation (P = 0.026-0.005), which was abolished by indomethacin pretreatment. A single instillation of travoprost or unoprostone and 7-day instillation of unoprostone showed no effect.

CONCLUSIONS

After a 7-day instillation in normal rabbit eyes, topical travoprost suppressed ET-1-induced vasoconstrictive effects only in the ipsilateral posterior retina by its local effect; this effect was maintained at least for 30 min and mediated by endogenous prostaglandins.

Effects of topical 2% dorzolamide hydrochloride alone and in combination with 0.5% timolol maleate on intraocular pressure in normal feline eyes

OBJECTIVE

To evaluate the effect of topical 2% dorzolamide alone, and in combination with topical 0.5% timolol, on intraocular pressure (IOP) in normal cats.

ANIMALS

Twenty-four healthy Domestic Short-haired cats.

PROCEDURE

Baseline values of IOP were established at 7 am, 10 am, 1 pm, 5 pm and 9 pm during pretreatment phase (days 1-2). During treatment phase (days 3-10) cats received 2% dorzolamide HCl q 12 h in group A (n = 6), q 8 h in group B (n = 6), and combined with 0.5% timolol maleate q 12 h in group C (n = 6). Cats in control group D (n = 6) received artificial tears q 8 h. During treatment phase IOP measurements were continued at the same time-points as in the pretreatment phase.

RESULTS

Mean pretreatment IOP in all cats was 18.46 +/- 2.99 mmHg. Mean IOP decreased significantly (P < 0.0086) in all treatment groups compared to pretreatment values (group A: 16.40 +/- 0.49 mmHg, group B: 16.04 +/- 0.49 mmHg, group C: 17.76 +/- 0.49 mmHg). IOP did not decrease in control group D (18.55 +/- 0.49 mmHg). The difference in IOP between treatment groups (A, B, C) was not statistically significant, but comparison of IOP between each treatment group and the control group was statistically significant (A-D; P = 0.0057; B-D, P = 0.0012; C-D, P = 0.0212).

CONCLUSION

Topical 2% dorzolamide significantly lowers IOP in normal cats but the effect is mild. Concomitant application of 2% dorzolamide and 0.5% timolol does significantly decrease IOP, but the effect is not significantly greater than q 8 h administration of dorzolamide alone.

Topical dorzolamide 2%/timolol 0.5% ophthalmic solution: a review of its use in the treatment of glaucoma and ocular hypertension

Topically administered dorzolamide 2%/timolol 0.5% (dorzolamide/timolol ophthalmic solution; Cosopt) is a fixed combination of two ocular hypotensive drugs (the carbonic anhydrase inhibitor dorzolamide and the beta-adrenoceptor antagonist timolol) that have an additive effect on lowering intraocular pressure (IOP) when administered together. This product is indicated for the treatment of elevated IOP in patients with open-angle glaucoma or ocular hypertension (OH) who are insufficiently responsive to topical beta-adrenoceptor antagonist monotherapy. As such, it can be considered for use in individuals who, as a consequence of failing to achieve target IOP with beta-adrenoceptor antagonist monotherapy, require the addition or substitution of another class of topical antiglaucoma medication. Clinical trials have demonstrated that dorzolamide/timolol (1 drop per eye twice daily) is an effective and generally well tolerated fixed combination for lowering IOP in patients with open angle glaucoma or OH, including individuals uncontrolled on beta-adrenoceptor antagonist monotherapy. Compared with concomitant therapy with the individual components, the primary advantage of fixed combination dorzolamide/timolol is convenience.

Comparison of the effects of topical administration of a fixed combination of dorzolamide-timolol to monotherapy with timolol or dorzolamide on IOP, pupil size, and heart rate in glaucomatous dogs

OBJECTIVE

To determine whether the combination multiple-dose dorzolamide-timolol administered topically has any greater effects on the reduction of intraocular pressure, pupil size, and heart rate in dogs with glaucoma than do either timolol or dorzolamide alone.

PROCEDURE

Applanation tonometry, pupil size, and heart rate measurements were made at 7 a.m., 1 p.m., and 7 p.m. daily of 12 laboratory Beagles with inherited primary open-angle glaucoma during each active phase of this study. Timolol 0.5% was administered first twice daily for 4 consecutive days. Dorzolamide 2.0% was administered next three times daily for 4 consecutive days. The fixed combination of the two (timolol 0.5% and dorzolamide 2.0%) was administered twice daily for 4 consecutive days during the final week of the study. Between administration of each drug, a withdrawal period of at least 10 days was instituted. Statistical comparisons between the effects of the three drugs were performed.

RESULTS

Intraocular pressure (IOP) was decreased with the administration of all three drugs: timolol alone, dorzolamide alone, and the combination of the two decreased IOP after 1 day of treatment 2.83 +/- 0.70 mmHg, 6.47 +/- 0.32 mmHg, and 6.56 +/- 0.37 mmHg, respectively. After 4 days of treatment, the IOP decreased even further: timolol alone, dorzolamide alone, and the combination of the two decreased IOP 3.75 +/- 0.88 mmHg, 7.50 +/- 0.29 mmHg, and 8.42 +/- 0.58 mmHg, respectively. Heart rate was significantly decreased with timolol (-11.9 +/- 2.0 bpm) and the combination preparation (-8.6 + 2.4 bpm), but not with dorzolamide (-3.7 +/- 1.8 bpm) alone. Pupil size was significantly decreased with timolol (-1.42 + 0.40 mm) and the combination preparation (-1.3 + 0.33 mm), but not with dorzolamide (0.97 +/- 0.36 mm) alone.

CONCLUSIONS

The combination dorzolamide-timolol appears to be more effective at reducing intraocular pressure in glaucomatous dogs than is either timolol or dorzolamide alone.

Dorzolamide and timolol saves retinal ganglion cells in glaucomatous adult rats

PURPOSE

This study was designed to evaluate the effects of a dorzolamide-timolol combination or dorzolamide on retinal ganglion cell (RGC) density and intraocular pressure (IOP) in glaucomatous eyes of adult rats.

METHODS

Glaucoma was induced in the right eye of adult Wistar rats by episcleral venous occlusion. One experimental group was administered dorzolamide 2%-timolol 0.5% combination eye drops, while the other experimental group was administered dorzolamide 2% eye drops. Control groups had surgery without drug administration. Drug application was initiated either 2 weeks before surgery (Group A), from the day of surgery (Group B), 2 weeks after surgery (Group C), or 4 weeks after surgery (Group D). RGCs were labeled by intratectal Fluorogold injections and counted from flat-mount preparations, and IOP was measured using Tonopen.

RESULTS

Both dorzolamide-timolol combination and dorzolamide, when applied topically, significantly reduced IOP and improved RGC densities in experimental eyes when compared to control eyes. Earlier initiation, as well as longer duration of drug application, resulted in higher RGC densities.

CONCLUSIONS

Topical application of a dorzolamide-timolol combination or dorzolamide saved RGCs to a significant extent and reduced IOP in glaucomatous rat eyes.

Effect of topical dorzolamide on rabbit central corneal thickness

Our objective was to study the effect of dorzolamide on corneal hydration in an 18-week controlled experiment using ultrasonic pachymetry. Twenty-eight male rabbits were divided randomly into four groups. The 7 rabbits in each group received eye drops containing either 2% (w/v) dorzolamide or placebo in their right eye, or in their left eye. The 2% dorzolamide rabbits were treated every 8 h. Fellow eyes are defined as eyes which did not receive either dorzolamide or placebo. The study was blind for both the person who applied the drug and the one who performed the pachymetry. The effect of treatments is reported on the basis of the percentage of pachymetric variation compared to the measurement made before drug application. There was no significant difference (P = 0.061) in pachymetric variation between dorzolamide (-4.42 +/- 11.71%) and placebo (2.48 +/- 9.63%). However, there was a significant difference (P = 0.0034) in pachymetric variation between the dorzolamide fellow eyes (-7.56 +/- 10.50%) and the placebo (-4.42 +/- 11.71%). In conclusion, dorzolamide did not increase the corneal thickness in rabbits.

Ocular hypotensive drugs

The glaucomas are vision-threatening diseases that commonly result in blindness. In addition to knowledge of the at-risk breeds and predisposing factors for glaucoma as well as the clinical signs of the disease, regular IOP screening with tonometry is required to confirm glaucoma and to monitor the status of the eye. Early intervention with a combination of medications that are capable, in a given species, of reducing aqueous production and increasing aqueous outflow as well as potentially reducing progressive neurosensory degeneration is key to the medical management of this disease.

The effects of antiglaucoma and systemic medications on ocular blood flow

Based on the body of evidence implicating ocular blood flow disturbances in the pathogenesis of glaucoma, there is great interest in the investigation of the effects of antiglaucoma drugs and systemic medications on the various ocular vascular beds. The primary aim of this article was to review the current data available on the effects of antiglaucoma drugs and systemic medications on ocular blood flow. We performed a literature search in November 2002, which consisted of a textword search in MEDLINE for the years 1968-2002. The results of this review suggest that there is a severe lack of well-designed long-term studies investigating the effects of antiglaucoma and systemic medications on ocular blood flow in glaucomatous patients. However, among the 136 articles dealing with the effect of antiglaucoma drugs on ocular blood flow, only 36 (26.5%) investigated the effects of medications on glaucoma patients. Among these 36 articles, only 3 (8.3%) were long-term studies, and only 16 (44.4%) were double-masked, randomized, prospective trials. Among the 33 articles describing the effects of systemic medications on ocular blood flow, only 11 (33.3%) investigated glaucoma patients, of which only one (9.1%) was a double-masked, randomized, prospective trial. Based on this preliminary data, we would intimate that few antiglaucoma medications have the potential to directly improve ocular blood flow. Unoprostone appears to have a reproducible antiendothelin-1 effect, betaxolol may exert a calcium-channel blocker action, apraclonidine consistently leads to anterior segment vasoconstriction, and carbonic anhydrase inhibitors seem to accelerate the retinal circulation. Longitudinal, prospective, randomized trials are needed to investigate the effects of vasoactive substances with no hypotensive effect on the progression of glaucoma.

Effects of twice daily application of 2% dorzolamide on intraocular pressure in normal cats

The effect of the topical carbonic anhydrase inhibitor, dorzolamide, on intraocular pressure in cats was studied. The intraocular pressure of both eyes of eight healthy cats was measured using applanation tonometery (Tono-Pen) during two phases: control and treatment. Both eyes were treated with 2% dorzolamide twice a day during the treatment phase. Application of dorzolamide resulted in a significant decrease of intraocular pressure over the treatment phase. By the fourth and fifth day of treatment, the mean intraocular pressure (+/- standard deviation) was 9.7 (+/- 1.5) mmHg, whereas the mean (+/- standard deviation) for the last 2 days of the control period was 12.2 (+/- 2.0) mmHg. Based on this study, dorzolamide is a potentially effective treatment for glaucoma in cats, significantly lowering intraocular pressure.

Clinical pharmacokinetics of dorzolamide

Dorzolamide is a carbonic anhydrase inhibitor for topical ophthalmic application. It is used in the treatment of glaucoma to lower the intraocular pressure. After absorption via the cornea and stroma, it inhibits carbonic anhydrase in the ciliary process, which leads to a reduction of aqueous humour production and therefore to the desired therapeutic effect. In the systemic circulation, dorzolamide is bound mainly to carbonic anhydrase in red blood cells. It is slowly metabolised to N-de-ethyldorzolamide, which in turn is also stored in red blood cells. The very slow elimination (half-life >4 months) of both substances takes place via the renal route. However, the inhibition of carbonic anhydrase in red blood cells is moderate in the course of a topical treatment, avoiding systemic adverse effects. This review summarises the pharmacokinetic and pharmacodynamic properties of dorzolamide and its metabolite in eye tissues and in the systemic circulation.

Effect of dorzolamide timolol combination versus timolol 0.5% on ocular bloodflow in patients with primary open-angle glaucoma

PURPOSE

Addition of dorzolamide to timolol in primary open-angle glaucoma shows augmented reduction of intraocular pressure. It is unknown as yet if addition of dorzolamide will alter hemodynamics.

METHODS

Fifteen patients with primary open-angle glaucoma were placed on a medication-dependent 1-week to 4-week washout that included maintenance on timolol. After washout, baseline measurements were taken (timolol). They were studied after a month on timolol or dorzolamide-timolol (Cosopt; Merck, Inc, Whitehouse Station, New Jersey), with the second drug preceded by another month of timolol maintenance and second baseline measurements. At each visit, visual function, intraocular pressure, and ocular hemodynamics were monitored, including indocyanine green and fluorescein angiography and color Doppler imaging.

RESULTS

Cosopt significantly reduced intraocular pressure (14.7 to 13.4 mm Hg, P <.05) and increased arteriovenous passage time (superior temporal artery) of fluorescein dye (2.13 to 1.76 seconds, P =.01) but had no effect on visual function.

CONCLUSIONS

When compared with timolol in primary open-angle glaucoma, Cosopt augments ocular tension reduction and reduces the amount of time required for blood to pass through the superior retinal vasculature.

The feline glaucomas: 82 cases (1995-1999)

OBJECTIVE

To describe signalment, ophthalmic abnormalities, and response to treatment in cats with glaucoma.

DESIGN

Retrospective study.

ANIMALS

Eighty-two cats with 93 glaucomatous eyes. CRITERIA FOR INCLUSION: Medical records of all cats with glaucoma presented to the ophthalmology services at two referral specialty hospitals between 1995 and 1999 were reviewed. Cats were included if intraocular pressure (IOP) > 25 mmHg, if buphthalmos was present, or if a shallow anterior chamber was present and IOP > or = 5 mm Hg higher than the contralateral normal eye.

RESULTS

Mean +/- SD age was 9.2 +/- 4.4 years. Thirty-one cats were female; 51 were male. Breeds included 69 domestic and 13 pure-bred cats. One eye was affected in 71 cats; both eyes in 11 cats. The most common presenting complaints and ophthalmic abnormalities were cataract, corneal edema, mydriasis, buphthalmos, cloudy eye, and blindness. Mean intraocular pressure in the affected eye was 36.4 +/- 14.7 mmHg. The glaucomas were believed to be secondary in 81 eyes, primary in five eyes, and undetermined in seven eyes. The goal of medical therapy was to maintain IOP in a comfortable range we presumed to be < 30 mm Hg in blind eyes, and to maintain IOP below 25 mmHg to preserve vision in visual eyes. Intraocular pressure was maintained in a comfortable range or normal range in 58% of all eyes using medical therapy alone. Surgery was performed in nine eyes after medical management failed. Sixty-seven eyes were blind, 21 were visual, and five had decreased vision at initial presentation. With treatment, vision was retained in nine eyes, deteriorated in five eyes, and was lost in three eyes.

CONCLUSIONS

The glaucomas were most frequently secondary in cats and resulted in blindness prior to presentation in the majority of eyes in our study. Medical management controlled IOP in more than half of the eyes, and maintained vision in almost half of visual eyes.

Changes in intraocular pressure associated with topical dorzolamide and oral methazolamide in glaucomatous dogs

OBJECTIVE

To compare the reduction in intraocular pressure (IOP) by topical 2% dorzolamide to oral methazolamide (5 mg/kg) in dogs, and determine if the combination of both drugs would reduce IOP more than either drug administered alone.

ANIMALS STUDIED

Thirteen glaucomatous beagles.

PROCEDURES

Measurements, including applanation tonometry, pupil size and heart rate, were obtained at 8 am, 12 noon, and 5 pm on days 1, 3 and 5. The 5-day drug studies included placebo (0.5% methylcellulose); 2% dorzolamide administered in one eye twice daily (8 am and 5 pm), and repeated again in one eye three times (8 am, 12 noon and 5 pm) daily; methazolamide (5 mg/kg per os administered at 8 am and 5 pm); 2% dorzolamide instilled twice daily (5 days) combined with oral methazolamide on the last 3 days, and methazolamide (5 days) combined with 2% dorzolamide on the last 3 days and instilled twice daily. Statistical comparisons between drug groups included control (nondrug) eye and treated (placebo/drug) eyes for days 1, day 3 and 5.

RESULTS

Topical 2% dorzolamide, administered twice and three times daily, significantly decreased IOP (mean +/- SEM) in glaucomatous dogs on the first day (twice daily 7.6 +/- 2.4 mmHg, and three times daily 16.4 +/- 3.6 mmHg) that was even greater by day 5 (twice daily 10.4 +/- 2.0 mmHg, and three times daily 13.9 +/- 2.7). Oral methazolamide also significantly lowered IOP in both eyes. Oral methazolamide (administered from day 1 through to day 5) combined with 2% topical dorzolamide (instilled in the drug eye for day 3 through to day 5) also significantly lowered IOP of both eyes for all days, and for day 5 the mean +/- SEM IOP was decreased by 7.9 +/- 1.7 mmHg (methazolamide plus dorzolamide) and 7.5 +/- 2.6 mmHg (methazolamide only). Topical dorzolamide (instilled in the drug eye for day 1 through to day 5) combined with oral methazolamide (administered from day 3 through to day 5) significantly lowered IOP in the drug eye on day 1 (5 pm: 9.6 +/- 1.9 mmHg), for day 3 (11 am and 5 pm) and for all of day 5 for both eyes (5 pm: control eye 9.5 +/- 1.8 mmHg; drug eye 9.2 +/- 1.9 mmHg). Topical dorzolamide (2%) instilled three times daily produces similar IOP declines compared to the combination of oral methazolamide and 2% dorzolamide administered twice daily.

CONCLUSIONS

Dorzolamide (2%) instilled twice or three times daily causes significant decreases in IOP in glaucomatous dogs. Twice daily instillations caused progressive declines in IOP from day 1 to day 5. Dorzolamide (2%) combined with oral methazolamide (5 mg/kg per os twice daily) produces similar but not additional declines in IOP.

Topical dorzolamide 2%/timolol 0.5%: a review of its use in the treatment of open-angle glaucoma

The nonselective beta-blocker timolol and the carbonic anhydrase inhibitor dorzolamide both lower intraocular pressure (IOP). Timolol and dorzolamide have different mechanisms of action and their effects are additive when administered together. Therefore, the 2 drugs are frequently used concomitantly to treat patients with open-angle glaucoma who have not adequately responded to first-line therapy. A barrier to good compliance with concomitant therapy is the need to administer 5 or 6 drops of medication on 2 or 4 occasions during the day. Timolol 0.5% and dorzolamide 2.0% have therefore been combined in a single formulation, reducing the number of administrations required to 2 per day. Clinical trials in patients with glaucoma have demonstrated that dorzolamide 2%/timolol 0.5% (dorzolamide/timolol) is superior to monotherapy with the individual components. When dorzolamide/timolol administered twice daily was compared with concomitant treatment with dorzolamide 2% and timolol 0.5%, each administered twice daily for 90 days, both regimens resulted in marked lowering of trough IOP (measured just before the morning dose) compared with baseline (reduction in IOP = 4.2mm Hg). The effect of the 2 regimens on IOP at all time points, both before treatment and at peak effect (2 hours after treatment), were virtually indistinguishable. When the combined formulation was compared with a concomitant regimen that included dorzolamide 2% 3 times daily and timolol 0.5% twice daily the concomitant regimen was slightly more efficacious than the combined regimen at trough after 90 days: IOP was lowered by 3.6mm Hg in the combined group versus 4.1 mm Hg in the concomitant group. Dorzolamide/timolol has been compared with concomitant administration of timolol 0.5% and the IOP lowering miotic drug, pilocarpine 2.0%. This non-blind patient-preference study found that both regimens reduced IOP. However, the dorzolamide/timolol combination was preferred by the patients because of reduced frequency and severity of adverse effects and less frequent administration. Dorzolamide/timolol was well tolerated in clinical trials, the adverse effects reflected those of the individual components, and no additional tolerability issues were identified. However, the potential for timolol to cause cardiorespiratory effects must be considered when prescribing this combination. Furthermore, dorzolamide is a sulfonamide and can cause allergic reactions in those who are hypersensitive to this class of drug.

CONCLUSIONS

Dorzolamide/timolol is a well tolerated and effective fixed combination for lowering IOP in the treatment of open-angle glaucoma and is likely to be useful in those patients who do not respond adequately to first-line monotherapy. Compared with concomitant therapy with the same 2 drugs the primary advantage is convenience, which may lead to improved compliance. Studies of compliance and comparisons with other currently available combination therapies would be useful to fully define the value of the formulation. Nonetheless, dorzolamide combined with timolol in a single applicator system will be a useful addition to the treatment options for glaucoma, a leading cause of preventable blindness.

Carbonic anhydrase inhibitors: sulfonamides incorporating furan-, thiophene- and pyrrole-carboxamido groups possess strong topical intraocular pressure lowering properties as aqueous suspensions

Important physiological and physio-pathological functions are played by several carbonic anhydrase (CA, EC 4.2.1.1) isozymes, which are strongly inhibited by aromatic and heterocyclic sulfonamides. Here we report several new types of such sulfonamides, incorporating furan-, thiophene- and pyrrole-carboxamide moieties in their molecules. Some of these compounds showed very good CA II and CA IV inhibitory properties. with affinities for the enzymes in the low nanomolar range. Due to their relatively low water solubility, some of the most active CA II inhibitors reported here have been formulated as aqueous suspension for topical administration as antiglaucoma agents. in normotensive and glaucomatous rabbits. The derivatives incorporating furan- and pyrrole-carboxamide moieties (but not the corresponding thiophene-substituted derivatives), showed effective and long-lasting intraocular pressure (IOP) lowering both in normotensive as well as glaucomatous animals, with potencies superior to dorzolamide and brinzolamide, the two available topically acting sulfonamide drugs. This is the first example of non-water soluble sulfonamides that significantly lower IOP, being thus similar with the recently introduced drug brinzolamide, which belongs to a completely different chemical family of antiglaucoma sulfonamides.

Pharmaceutical management of the childhood glaucomas

Glaucoma in childhood is a diverse, blinding group of conditions, which presents a major therapeutic challenge. Treatment is primarily surgical with medical treatments used as an adjunct. None of these drugs has been granted approval by the regulatory agencies for use in children, but they are used on a compassionate basis. Issues of efficacy and safety of these medications in children are discussed. beta-adrenoceptor blockers have been employed as first line pharmaceutical therapy for many years. Recently three new classes of drugs have been developed for use in glaucoma in adults. beta-blockers remain first line therapy if there are no contraindications such as asthma. Topical carbonic anhydrase inhibitors (CAI) appear to be less effective than beta-blockers, but seem safe systemically, although associated with local irritation. They are useful as an adjunct to beta-blockers or as first line therapy when beta-blockers are contraindicated. Prostaglandins have not proved as effective in childhood glaucoma as in adult glaucoma, although it works well in some patients with juvenile open angle glaucoma (JOAG) and others with aphakic glaucoma. alpha-adrenergic agonists, although effective at least in the short-term, have serious, potential systemic side effects, which demand close observation when used in neonates and young infants.

Pharmacological and ocular hypotensive properties of topical carbonic anhydrase inhibitors

There was a time gap of over 40 years between the demonstrated oral effectiveness of acetazolamide in lowering the intraocular pressure (IOP) of glaucoma patients and the introduction of a topical carbonic anhydrase (CA) inhibitor. This is due to the fact that CA-II, the isoenzyme which most likely plays an important role in the production of aqueous humor in humans, must be essentially inhibited by 100% to elicit a pharmacological response. The lack of success with earlier attempts to obtain a topical agent stems from an inability to attain and maintain a sufficiently high intraocular concentration of drug to achieve the required inhibition of CA. Dorzolamide and brinzolamide are two topical CA inhibitors which are currently available to treat ocular hypertension and/or glaucoma. Dorzolamide is a very potent inhibitor of CA-II and its site of action is local within the eye. Like oral CA inhibitors, topically applied dorzolamide lowers IOP by decreasing the production of aqueous humor. The drug is used in monotherapy as a 2% solution administered three times daily. Its ocular hypotensive effect is comparable to that of timolol at peak but is somewhat less at trough. The IOP lowering effect of timolol is enhanced by the twice daily administration of 2% dorzolamide either concomitantly or in combination. Topically applied dorzolamide is generally well tolerated and had a low drop-out rate in clinical studies. The most frequent ocular adverse experience is burning and/or stinging. Corneal and lenticular problems have generally not been encountered with long-term therapy with dorzolamide. Topically applied dorzolamide penetrates directly to the posterior segment of the eye and its presence is consistent with the initial report that dorzolamide increases retinal blood flow velocity in patients with normal tension glaucoma. The most frequent systemic adverse experience is a transient bitter taste. Biochemical changes indicative of the systemic inhibition of CA have not been observed in monotherapy studies lasting up to 2 years. This is in harmony with the inability of dorzolamide at steady-state to saturate CA in the red blood cell and the failure to detect its presence in plasma. A 1% suspension of brinzolamide is comparable to 2% dorzolamide in lowering IOP, both drugs being administered three times daily. Although brinzolamide has a lower incidence of burning/ stinging, it elicits more blurred vision.

Dorzolamide, visual function and ocular hemodynamics in normal-tension glaucoma

The purpose of this study was to determine how a topical carbonic anhydrase inhibitor, dorzolamide, alters visual function and ocular blood flow in persons with normal-tension glaucoma. Eighteen normal tension glaucoma patients, after washout of other ocular medications, were treated for four weeks with 2% dorzolamide, three times daily. A control group of eleven other normal-tension glaucoma patients received placebo eye drops. Patients were studied before treatment, and after two and four weeks of treatment. Each study included assessment of central visual function (contrast sensitivity), intraocular pressure (IOP), and several aspects of ocular hemodynamics, including measures of retinal arteriovenous passage time, retinal arterial and venous diameters, and flow velocities in the ophthalmic, central retinal, and posterior ciliary arteries. Dorzolamide significantly reduced IOP at two and four weeks (each p<0.01), and at the same time increased contrast sensitivity at both three and six cycles per degree (each p<0.05). Neither of these variables changed significantly in the control group. Dorzolamide also accelerated retinal arteriovenous passage time of fluorescein dye, at constant retinal arterial and venous diameters (p<0.05), but failed to change flow velocities in any retrobulbar vessel. The ability of dorzolamide to improve contrast sensitivity in persons with normal-tension glaucoma may be related to either IOP reduction or altered ocular perfusion.

The ocular distribution of methazolamide after corneal and scleral administration: the effect of ionization state

The accession of methazolamide in ionized and unionized form to cornea, sclera, aqueous humor and ciliary process was studied 10 minutes following separate application to either sclera or cornea of a 1 mM solution. Cornea and ciliary process concentrations were 27.3 and 14.5 microM for unionized application to cornea and 10.1 and 7.1 microM for ionized application. Bulk aqueous humor concentrations were much lower, 3.1 and 1.1 microM, and cannot account for drug found in ciliary process on this time scale. Scleral application of drug, by contrast, gave undetectable ciliary process concentrations. These results are presented as a model for drug disposition following single drop topical sulfonamide therapy. The scleral pathway for drug delivery to ciliary process was further tested by application to sclera of 300 microL of either a 1 mM ionized or unionized solution for 30 minutes or as a 2% (85.5 mM) ionized solution for 30 minutes. In these series, red cell carbonic anhydrase was presaturated at -24 hours with drug to remove a possible route for loss of drug from sclera, that of the systemic circulation and the high concentration of carbonic anhydrase in red cells. After either ionized or unionized application, approximately 1 microM was detected in ciliary process, but all drug was attributable to the blood content of the tissue and the drug bound to red cell carbonic anhydrase. After 2% dosing, 4 microM was detected in ciliary process after allowance for drug in red cells. This concentration is below that necessary for inhibition of ciliary process carbonic anhydrase, suggesting that especially with regard to topical sulfonamide therapy, the corneal route of drug delivery to ciliary process predominates greatly over the scleral route.

Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV with N-hydroxysulfonamides--a novel class of intraocular pressure lowering agents

A series of N-hydroxy sulfonamides has been prepared by reaction of alkyl-, arylalkyl- and arylsulfonyl halides or sulfonic acid anhydrides with hydroxylamine. Structurally related inhibitors were also obtained from acyl chlorides and hydroxylamine, as well as by reaction of tosyl isocyanate with hydroxylamine, sulfamic acid and sulfamide. Inhibition of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human; b = bovine) with the prepared compounds has been investigated. Good inhibitors, as well as compounds with moderate activity against these isozymes were detected, depending on the R group to which the SO2NHOH or CONHOH moieties were attached. Susceptibility to inhibition was generally: hCA II > bCA IV >> hCA I. Some of the new inhibitors showed very good antiglaucoma action when administered directly into the eye in experimental animals, acting as more efficient intraocular pressure lowering agents as compared to the clinical drug dorzolamide. This constitutes an encouraging result for obtaining novel antiglaucoma drugs from this class of CA inhibitors.

Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV with heterocyclic mercaptans, sulfenamides, sulfonamides and their metal complexes

A series of sulfenamides, sulfonamides and sulfonamide metal complexes have been prepared starting from 4,5-disubstituted-3-mercapto-1,2,4-triazole derivatives. The heterocyclic mercaptans were oxidized to the corresponding sulfenamides by hypochlorite in the presence of ammonia. The sulfonamides were obtained by oxidation of sulfenamides with potassium permanganate. The Zn(II) and Cu(II) complexes of the new heterocyclic sulfonamides have been prepared via the sodium salt of the ligand. Inhibition of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human, b = bovine) with the prepared compounds has been investigated. Mercaptans were generally less inhibitory than sulfenamides, which in turn behaved as weaker inhibitors than the sulfonamides. The strongest inhibitors were the Zn(II) and Cu(II) complexes of the heterocyclic sulfonamides. Susceptibility to inhibition was generally: hCA II > bCA IV > hCA I. Although none of the obtained simple inhibitors (mercaptans, sulfenamides, sulfonamides) possessed antiglaucoma action when administered directly into the eye in experimental animals, the Zn(II) and Cu(II) complexes of some sulfonamides acted as more efficient intraocular pressure lowering agents as compared to the clinical drug dorzolamide. This constitutes an encouraging result for obtaining novel antiglaucoma drugs from this class of CA inhibitors.

Dorzolamide. A review of its pharmacology and therapeutic potential in the management of glaucoma and ocular hypertension

Dorzolamide (dorzolamide hydrochloride), the first topical carbonic anhydrase (CA) inhibitor to become available for clinical use, lowers intraocular pressure (IOP) by reducing aqueous humour formation. It is formulated as a 2% eyedrop for use in the management of glaucoma and ocular hypertension. When administered 3 times daily, dorzolamide is effective in lowering IOP in patients with open-angle glaucoma or ocular hypertension. Mean IOP was reduced by approximately 4 to 6 mm Hg at peak (2 hours postdose) and 3 to 4.5 mm Hg at trough (8 hours postdose) in clinical trails. A 1-year comparative study showed that the ocular hypotensive efficacy of dorzolamine 2% 3 times daily was similar to that of betaxolol 0.5% twice daily, but slightly inferior to that of timolol 0.5% twice daily. Dorzolamide has additive ocular hypotensive effects when used in conjunction with topical beta-adrenergic antagonists and was as effective as pilocarpine 2% 4 times daily as adjunctive therapy in patients receiving timolol. Dorzolamide does not appear to produce the acid-base or electrolyte disturbances and severe systemic adverse events associated with oral CA inhibitors, and unlike beta-adrenergic antagonists, it is not contraindicated in patients with asthma, reactive airways disease or heart disease. Furthermore, as CA inhibitors do not cause miosis, they may cause less interference with vision than pilocarpine or epinephrine (adrenaline). The most common adverse effects associated with dorzolamide are bitter taste and transient local burning or stinging. Conjunctivitis was the most common reason for discontinuation of dorzolamide in one large study. Thus, available data suggest that dorzolamide has potential as an alternative therapy option in patients with glaucoma or ocular hypertension who are intolerant of, or unable to receive, ophthalmic beta-adrenergic antagonists and as adjunctive therapy in patients already receiving these agents. Further efficacy and tolerability data are needed to determine the place of dorzolamide in therapy.