Therapeutic potential of prostaglandin analogues in glaucoma

Glaucoma: Current treatment and impact of advanced drug delivery systems

The human eye being a complex and a very sensitive organ makes the drug delivery task challenging. An increase in the intra-ocular pressure at the aqueous humour leads to glaucoma which is not only indecipherable but can also be the reason of blindness for many. The presently available marketed formulations using anti-glaucoma drugs have issues of either difficulty in crossing the blood- retinal barrier or lower systemic bioavailability. Hence, the drugs having lower therapeutic index would need to be administered frequently, which eventually lead to deposition of concentrated solutions at ocular site, producing toxic effects and cellular damage to the eye. To overcome these drawbacks the novel drug delivery systems like In-situ gels, liposomes, niosomes, hydrogel, dendrimers, nanoparticles, solid lipid nanoparticles, Microneedles or ocular inserts play an important role to enhance the therapeutic efficacy of the anti-glaucomic drugs. The present review briefs the current treatments in terms of drugs used and in detail the impact of utilizing the above mentioned novel drug delivery systems in the treatment of glaucoma.

Conjunctival changes and inflammatory aspects in rabbits' conjunctivas induced by fixed combinations of prostaglandin analogues and timolol maleate

Background

The purpose of this research is to compare the histological and immunohistochemical changes induced by fixed combinations of timolol maleate and prostaglandin analogues in the rabbit conjunctiva. Thirty left eyes of rabbits, divided into three groups, were treated for 30 days with the following combinations of drugs: bimatoprost 0.03% + timolol 0.5%, travoprost 0.004% + timolol 0.5% and latanoprost 0.005 + timolol 0.5%. The right eyes served as controls and received no medication. At the end of the experiment, after enucleation, the conjunctivas were assessed through histomorphometry (number of inflammatory and goblet cells, epithelial thickness) and immunohistochemistry (anti-actin antibody to assess the degree of fibrosis).

Results

Histomorphometrically, there was infiltration of inflammatory cells in all the treated eyes. An increased number of goblet cells was observed with the use of all fixed combinations of prostaglandin analogues associated with timolol maleate in comparison with the control group. The combination travoprost + timolol resulted in more intense fibrosis. The effect of bimatoprost + timolol caused an intermediate reaction pattern among the other drugs, fostering higher numbers of goblet cells in the conjunctival epithelium, more than the other fixed combinations in this study. There was a difference in the comparison of goblet cells of eyes treated with bimatoprost + timolol (16.11 ± 2.42) and of those treated with latanoprost + timolol (13.18 ± 1.60) (P = 0.016).

Conclusion

It was found that all fixed combinations of prostaglandins analogues + timolol induce a reaction in the conjunctiva, increasing the inflammatory infiltrate.

Novel drug delivery systems for glaucoma

Reduction of intraocular pressure (IOP) by pharmaceutical or surgical means has long been the standard treatment for glaucoma. A number of excellent drugs are available that are effective in reducing IOP. These drugs are typically applied as eye drops. However, patient adherence can be poor, thus reducing the clinical efficacy of the drugs. Several novel delivery systems designed to address the issue of adherence and to ensure consistent reduction of IOP are currently under development. These delivery systems include contact lenses-releasing glaucoma medications, injectables such as biodegradable micro- and nanoparticles, and surgically implanted systems. These new technologies are aimed at increasing clinical efficacy by offering multiple delivery options and are capable of managing IOP for several months. There is also a desire to have complementary neuroprotective approaches for those who continue to show progression, despite IOP reduction. Many potential neuroprotective agents are not suitable for traditional oral or drop formulations. Their potential is dependent on developing suitable delivery systems that can provide the drugs in a sustained, local manner to the retina and optic nerve. Drug delivery systems have the potential to improve patient adherence, reduce side effects, increase efficacy, and ultimately, preserve sight for glaucoma patients. In this review, we discuss benefits and limitations of the current systems of delivery and application, as well as those on the horizon.

Travoprost compared with other prostaglandin analogues or timolol in patients with open-angle glaucoma or ocular hypertension: meta-analysis of randomized controlled trials

BACKGROUND

It is still uncertain whether travoprost has comparable or better efficacy compared with other prostaglandin analogues or timolol in patients with open-angle glaucoma or ocular hypertension. The authors performed a meta-analysis of randomized controlled trials to evaluate the incidence of reported side-effects and intraocular pressure (IOP)-lowering effect of travoprost versus other prostaglandin analogues (latanaprost, bimatoprost, unoprostone) or timolol.

METHODS

Systematic literature retrieval was conducted in Pubmed, EMBASE, Chinese Bio-medicine Database and Cochrane Controlled Trials Register to identify the potentially relevant randomized controlled trials. The statistical analysis was performed by RevMan 4.1 software that was provided by the Cochrane Collaboration. The outcome measures were the incidence of reported side-effects (hyperaemia, iris pigmentation, eyelash changes) and mean IOP pooled over treatment visits.

RESULTS

In total, 12 articles involving 3048 patients with open-angle glaucoma or ocular hypertension were included in this meta-analysis. The combined results showed that travoprost 0.004% was more effective than timolol or travoprost 0.0015% in lowering IOP, but not more effective than bimatoprost or latanoprost. Travoprost 0.004% caused a higher percentage of hyperaemia than timolol, latanoprost, or travoprost 0.0015%. There was an increased incidence of pigmentation with travoprost than timolol. Travoprost 0.004% caused a higher percentage of eyelash changes than timolol, latanoprost, or travoprost 0.0015%.

CONCLUSION

According to data available, travoprost is more effective than timolol in lowering IOP in patients with open-angle glaucoma or ocular hypertension. Compared with other prostaglandin analogues, travoprost appears to be equivalent to bimatoprost and latanoprost. Although a limited number of local side-effects were reported, no serious treatment-related side-effects were reported.

Cellular and molecular effects of unoprostone as a BK channel activator

Effects of unoprostone isopropyl (unoprostone), a prostaglandin metabolite analog; latanoprost, a PGF(2alpha) analog; and PGF(2alpha) were examined in HCN-1A cells, a model system for studies of large conductance Ca(2+) activated K(+)(BK) channel activator-based neuroprotective agents. Unoprostone and latanoprost, both used as anti-glaucoma agents, have been suggested to act through FP receptors and have neuroprotective effects. Ion channel activation, plasma membrane polarization, [Ca(2+)](i) changes and protection against long-term irreversible glutamate-induced [Ca(2+)](i) increases were studied. Unoprostone activated iberiotoxin (IbTX)-sensitive BK channels in HCN-1A cells with an EC(50) of 0.6+/-0.2 nM and had no effect on Cl(-) currents. Unoprostone caused IbTX-sensitive plasma membrane hyperpolarization that was insensitive to AL8810, an FP receptor antagonist. In contrast, latanoprost and PGF(2alpha) activated a Cl(-) current sensitive to [Ca(2+)](i) chelation, tamoxifen and AL8810, and caused IbTX-insensitive, AL8810-sensitive membrane depolarization consistent with FP receptor-mediated Ca(2+) signaling Cl(-) current activation. Latanoprost and PGF(2alpha), but not unoprostone, increased [Ca(2+)](i). Unoprostone, PGF(2alpha) only partially, but not latanoprost protected HCN-1A cells against glutamate-induced Ca(2+) deregulation. These findings show that unoprostone has a distinctly different mechanism of action from latanoprost and PGF(2alpha). Whether unoprostone affects the BK channel directly or an unidentified signaling mechanism has not been determined.

The effects of prostaglandin analogues on the blood aqueous barrier and corneal thickness of phakic patients with primary open-angle glaucoma and ocular hypertension

PURPOSE

To evaluate the effects of topical latanoprost, travoprost, and bimatoprost on the blood-aqueous barrier and central corneal thickness (CCT) of patients with primary open-angle glaucoma (POAG) and ocular hypertension (OHT).

DESIGN

Prospective, randomized, masked-observer, crossover clinical trial.

METHODS

A total of 34 phakic patients with POAG or OHT with no previous history of intraocular surgery or uveitis completed the study. Patients were randomized to use latanoprost 0.005%, travoprost 0.004%, or bimatoprost 0.03% once daily (2000 hours) for 1 month, followed by a washout period of 4 weeks between each drug. Aqueous flare was measured with a laser flare metre. CCT was calculated as the average of five measurements using ultrasound pachymetry. All measurements were performed by a masked observer (1000 h).

RESULTS

There were no statistically significant differences between baseline mean IOP, mean CCT, and mean flare values among the groups. There was no statistically significant increase in mean flare values from baseline in all groups (P>0.05). There were no statistically significant differences between mean flare values among the groups (P>0.05). All medications significantly reduced the mean IOP from baseline (P<0.0001). IOP reduction obtained with travoprost (7.3+/-3.8 mmHg) was significantly higher than that obtained with latanoprost (4.7+/-4.2 mmHg) (P=0.01). A statistically significant reduction in mean CCT (0.6+/-1.3%) from baseline was observed when patients instilled bimatoprost (P=0.01).

CONCLUSIONS

Latanoprost, travoprost, and bimatoprost had no statistically significant effect on the blood-aqueous barrier of phakic patients with POAG or OHT. Bimatoprost may be associated with a clinically irrelevant reduction in mean CCT.

Advances in glaucoma therapeutics

Glaucoma is a major cause of irreversible blindness in the world. The prevalence of glaucomatous loss in vision will continue to grow as our populations age. Ocular hypertension is a major risk factor for the development of glaucoma and current glaucoma therapy is directed at lowering intraocular pressure. Several new ocular hypotensive agents have been introduced in the past several years providing a variety of treatment options. In addition, various classes of neuroprotective agents demonstrating activity in a wide variety of animal models have been proposed as potential new glaucoma therapeutics. Although these approaches will slow the progression of vision loss, they do not directly intervene in the disease process(es). Advances have been made attempting to understand the pathogenic pathways involved in glaucomatous damage to the eye and in methods to clinically measure glaucoma damage. An increased understanding of the pathophysiology of glaucoma will lead to the development of new therapeutic agents that intervene and perhaps even reverse glaucomatous damage to the eye. There also is a need to develop new methods to clinically measure glaucoma damage because, currently, considerable damage occurs before glaucoma is diagnosed and glaucoma remains underdiagnosed in the general population.

Nonsteroidal anti-inflammatory drugs in veterinary ophthalmology

Uveitis is a common sequela to many ocular diseases. Primary treatment goals for uveitis should be to halt inflammation, prevent or control complications caused by inflammation, relieve pain, and preserve vision. Systemic and topical NSAIDs are essential components of the pharmaceutic armamentarium currently employed in the management of ocular inflammation by general practitioners and veterinary ophthalmologists worldwide. NSAIDs effectively prevent intraoperative miosis; control postoperative pain and inflammation after intraocular procedures, thus optimizing surgical outcome; control symptoms of allergic conjunctivitis;alleviate pain from various causes of uveitis; and circumvent some of the unwanted side effects that occur with corticosteroid treatment. Systemic NSAID therapy is necessary to treat posterior uveitis, because therapeutic concentrations cannot be attained in the retina and choroid with topical administration alone, and is warranted when diseases, such as diabetes mellitus or systemic infection, preclude the use of systemic corticosteroids. Risk factors have been identified with systemic and topical administration of NSAIDs. In general, ophthalmic NSAIDs may be used safely with other ophthalmic pharmaceutics; however, concurrent use of drugs known to affect the corneal epithelium adversely, such as gentamicin, may lead to increased corneal penetration of the NSAID. The concurrent use of NSAIDs with topical corticosteroids in the face of significant preexisting corneal inflammation has been identified as a risk factor in precipitating corneal erosions and melts in people and should be undertaken with caution[8]. Clinicians should remain vigilant in their screening of ophthalmic and systemic complications secondary to drug therapy and educate owners accordingly. If a sudden increase in patient ocular pain (as manifested by an increase in blepharospasm, photophobia, ocular discharge, or rubbing)is noted, owners should be instructed to contact their veterinarian promptly.

Latanoprost : an update of its use in glaucoma and ocular hypertension

Latanoprost (Xalatan) is an ester analogue of prostaglandin F2alpha that reduces intraocular pressure (IOP) by increasing uveoscleral outflow. The IOP-lowering efficacy of latanoprost 0.005% lasts for up to 24 hours after a single topical dose, which allows for a once-daily dosage regimen. In patients with ocular hypertension or open-angle glaucoma, a single drop of latanoprost 0.005% solution (about 1.5 microg) administered topically once daily reduced diurnal IOP by 22 to 39% over 1 to 12 months' treatment in well-controlled trials; efficacy was maintained during treatment periods of up to 2 years. At this dosage, latanoprost was significantly more effective than timolol 0.5% twice daily in 3 of 4 large, double-blind, randomised studies, was generally as effective as bimatoprost or travoprost, and was significantly more effective than dorzolamide, brimonidine or unoprostone. Furthermore, in patients whose IOP was poorly controlled with timolol, switching to latanoprost monotherapy was at least as effective at lowering IOP as adding dorzolamide or pilocarpine to the regimen. Latanoprost has also shown significant additive effects when used in combination with one or more other glaucoma medications. The fixed combination of latanoprost plus timolol was significantly more effective than either of its individual components in two double-blind randomised studies and more effective than the fixed combination of dorzolamide and timolol in a 3-month, evaluator-masked study. Data in patients with angle-closure glaucoma are limited, but in patients with elevated IOP after undergoing iridotomy, latanoprost 0.005% once daily was significantly more effective than timolol 0.5% twice daily at reducing IOP over 12 weeks of treatment in a large double-blind, randomised study. Latanoprost is generally well tolerated and, unlike timolol, induces minimal systemic adverse events. In well-controlled, 6-month trials, the most commonly occurring drug-related ocular events in latanoprost recipients were mild to moderate conjunctival hyperaemia (3 to 15%) and iris colour change (2 to 9%); these seldom required patient withdrawal although the latter may be permanent. Latanoprost 0.005% as a single daily drop has shown good IOP-lowering efficacy in patients with open-angle glaucoma or ocular hypertension and does not produce the cardiopulmonary adverse effects associated with beta-blockers. Thus, latanoprost is a valuable addition to the first-line treatment options for patients with open-angle glaucoma or ocular hypertension. In addition, adjunctive treatment with latanoprost in patients who are refractory to beta-blocker therapy is a viable, second-line treatment option. Although preliminary findings are promising, wider clinical experience is required to define the place of latanoprost in the treatment of angle-closure glaucoma.

Trends in Glaucoma Surgery before and after the Introduction of New Topical Glaucoma Pharmacotherapies

OBJECTIVE

Recent advances in pharmacotherapy that have improved the ability to effect sustained reductions in intraocular pressure may delay or obviate the need for surgery for open-angle glaucoma. This analysis explored this possibility by evaluating the frequency of surgeries for open-angle glaucoma in the US Medicare population before and after the 1996 introduction of latanoprost, a topical prostaglandin analogue with potent ocular antihypertensive efficacy and a better safety profile than older topical glaucoma medications.

METHODS

Data from the Medicare 5% Standard Analytical File were used to develop national estimates of the frequency of glaucoma surgeries in the US yearly from 1994 through 1999.

RESULTS

While the number of US Medicare patients with a diagnosis of glaucoma remained constant from 1994 through 1999, the number of inpatient and outpatient glaucoma surgeries declined with a particularly sharp drop between 1996 and 1997. In 1999 relative to 1994, the number of annual glaucoma surgeries among unique patients with a diagnosis of glaucoma was reduced by 72% for inpatient procedures and 42% for outpatient procedures.

CONCLUSIONS

The number of glaucoma surgeries among US Medicare patients markedly decreased from 1994 to 1999, during which time the prevalence of glaucoma remained stable in this population. The decrease in surgeries coincided with the introduction of improved topical pharmacotherapies for the management of glaucoma. Although the ability to infer a causal relationship between introduction of new pharmacotherapy and the decrease in surgeries is limited, the consistency of these data with those of several other studies renders the findings compelling.

Comparative effects of latanoprost (Xalatan) and unoprostone (Rescula) in patients with open-angle glaucoma and suspected glaucoma

PURPOSE

To compare, in paired eyes of open-angle glaucoma patients and glaucoma suspects, hydrodynamic and visual changes after 1 month of topical latanoprost in one eye and unoprostone in the other.

DESIGN

Single-center, institutional randomized clinical trial.

METHODS

After completing a washout period off all topical medication, 25 adults (mean age 54 +/- SEM 2 years) with bilateral open-angle glaucoma or glaucoma suspect status underwent morning (8 to 10 AM) and afternoon (1 to 3 PM) measurements of intraocular pressure (IOP), pulsatile ocular blood flow (POBF), contrast, sensitivity, frequency doubling technology, and Humphrey 10-2 perimetry (HVFA II) in both eyes. Each then started unoprostone 0.15% (Rescula) in one randomly assigned eye and latanoprost 0.005% (Xalatan) in the other. Unoprostone was administered at 8 AM and 8 PM and latanoprost at 8 PM with placebo at 8 AM, both from masked bottles. After 28 days, differences were determined for each measured variable by two-tailed paired t test.

RESULTS

Starting from similar baseline IOP levels, after 1 month of treatment, the mean morning IOP values differed according to the topical agent received (16.2 +/- SEM 0.6 mm Hg for latanoprost vs 17.9 +/- 0.7 mm Hg for unoprostone; P =.001). These morning pressures were 2.6 mm Hg lower than baseline in the eyes receiving latanoprost (P <.0001), and 1.6 mm Hg lower in unoprostone-treated eyes (P =.02). Afternoon values were 3.1 +/- SEM 0.6 lower than corresponding baseline in eyes receiving latanoprost, and 2.4 +/- SEM 0.6 mm Hg in unoprostone-treated eyes (P <.0001 from baseline for both medications; interdrug mean IOP difference; P =.04). Eyes receiving unoprostone showed a 1.7-db improvement in frequency doubling mean deviation (P =.03), the only significant visual function change observed. Pulsatile ocular blood flow increased 30% relative to baseline in eyes receiving latanoprost, (P <.0001) and 16% in eyes receiving unoprostone (P =.05) by the morning of day 28. That afternoon, mean POBF had increased 30% (P <.0001) relative to afternoon baseline values among eyes receiving latanoprost and 18% (P =.03) among those receiving unoprostone (interdrug change difference, P =.05). Humphrey perimetry and contrast sensitivity remained stable with both prostanoids.

CONCLUSIONS

Both latanoprost and unoprostone produced significant reductions in IOP and increases in POBF, with stable central and perimacular visual function. Latanoprost once daily produced IOP reduction and POBF increases nearly twofold greater than those obtained with unoprostone twice daily. These differences in IOP and POBF change between unoprostone and latanoprost were statistically significant.