Systemic side effects from ophthalmic timolol and their prevention

An Evaluation of the Efficacy and Safety of Timolol Maleate 0.5% Microdrops Administered with the Nanodropper

PURPOSE

To examine if 12.5 μl timolol maleate 0.5% microdrops dispensed with the Nanodropper Adaptor provide noninferior intraocular pressure (IOP) reduction compared with conventional 28 μl drops in patients with open-angle glaucoma (OAG) and ocular hypertension (OHT).

DESIGN

Prospective, noninferiority, parallel, multicenter, single-masked, active-controlled, randomized trial.

PARTICIPANTS

Treatment-naïve subjects who were recently diagnosed with OAG and OHT at the Aravind Eye Care System.

METHODS

Both eyes of subjects received 1 commercially available drop or both eyes of subjects received 1 microdrop of timolol maleate 0.5%. We measured IOP, resting heart rate (HR), and blood pressure (BP) at baseline and 1, 2, 5, and 8 hours after timolol administration.

MAIN OUTCOME MEASURES

The IOP was the primary outcome measure. Secondary outcomes were resting HR, systolic BP (sBP), and diastolic BP (dBP).

RESULTS

Adaptor-mediated microdrops and conventional drops of timolol significantly decreased IOP compared with baseline at all timepoints. Noninferiority was established at 3 of 4 timepoints. Heart rate decreases with Nanodropper were approximately 3 beats per minute (bpm) less than with conventional drops.

CONCLUSIONS

Timolol microdrops appear to be as effective in ocular hypotensive action as conventional drops with a slightly attenuated effect on resting HR and BP.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Effects of Topic Delivery of an Inhibitor of Serine Racemase on Laser-Induced Choroidal Vasculopathy

Purpose

Intravitreal injection of anti-VEGF antibodies remains the primary therapy for exudative age-related macular degeneration (exAMD), although its efficacy is limited. Previous research has demonstrated that both a loss-of-function mutation of srr and the intravenous injection of a serine racemase inhibitor, L-aspartic acid β-hydroxamate (L-ABH), significantly inhibit laser-induced choroidal neovascularization (CNV) in mice. Given that L-ABH is a small molecule, this study investigated the effects of L-ABH administered via eye drops on CNV, aiming to develop a noninvasive treatment strategy for exAMD.

Methods

CNV models in mice and rhesus macaques were established through laser photocoagulation. Seven monkeys were randomly assigned to receive either saline solution or L-ABH eye drops. Intraperitoneal or intravenous injection of fluorescein characterized CNV in both mice and monkeys. Fluorescein fundus angiography was used to assess leakage, whereas optical coherence tomography measured retinal thickness in the monkeys.

Results

L-ABH eye drops significantly reduced fluorescein leakage in laser-injured mice (P < 0.001 compared to saline). In laser-injured rhesus macaques, the average percent changes in leakage areas treated with L-ABH were 2.5% ± 25.8% (P = 0.004) and 1.5% ± 75.7% (P = 0.023 compared to saline solution) on day 14 and day 28, respectively. However, L-ABH eye drops did not significantly affect the number of grade IV laser spots or retinal thickness, whereas bevacizumab did.

Conclusions

This study demonstrates the potential efficacy of an SRR inhibitor in two animal models of laser-induced CNV.

Translational Relevance

This represents the first investigation into the effects of topical delivery of an SRR inhibitor on CNV.

Cationic-motif-modified exosomes for mRNA delivery to retinal photoreceptors

Topical treatment of vitreoretinal diseases remains a challenge due to slow corneal uptake and systemic clearance. Exosomes are emerging nanocarriers for drug delivery due to biocompatibility and cellular targeting properties. To apply them for retinal targeting via the topical route, exosomes must traverse various ocular barriers including the cornea, lens, vitreous humor (VH), and the retina itself. Here we engineered high-purity milk-derived exosomes by anchoring arginine-rich cationic motifs via PEG2000 lipid insertion on their surface. Modification enabled exosomes to use weak-reversible electrostatic interactions with anionic glycosaminoglycan (GAG) and water content of the tissue to enhance their transport rate and retention. Addition of cationic motifs neutralized the anionic surface charge of exosomes (-24 to -2 mV) without impacting size or morphology. Cationic-motif-modified exosomes exhibited two-fold faster steady state diffusivity through bovine corneas compared to unmodified exosomes. Fluorescence recovery after photobleaching confirmed that cationic-motif-modified exosomes can diffuse through VH without steric hindrance. In healthy VH, cationic-motif-modified exosomes demonstrated stronger binding resulting in three-fold lower average diffusivity that enhanced by six-fold in 50% GAG-depleted VH recapitulating advanced liquefaction. Cationic-motif-modified exosomes penetrated through the full-thickness of porcine retinal explants resulting in ten-fold higher uptake in photoreceptors and three-fold greater transfection with encapsulated eGFP mRNA compared to unmodified exosomes. Cationic-motif-modified exosomes are safe to use as they did not adversely affect the mechanical swelling properties of the cornea or lens nor impact retinal cell viability. Cationic-motif-modified exosomes, therefore, offer themselves as a cell-free nanocarrier platform for gene delivery to retinal photoreceptors potentially via the topical route.

Topical Drug Delivery to the Posterior Segment of the Eye

Topical drug delivery to the posterior segment of the eye is a very complex challenge. However, topical delivery is highly desired, to achieve an easy-to-use treatment option for retinal diseases. In this review, we focus on the drug characteristics that are relevant to succeed in this challenge. An overview on the ocular barriers that need to be overcome and some relevant animal models to study ocular pharmacokinetics are given. Furthermore, a summary of substances that were able to reach the posterior segment after eye drop application is provided, as well as an outline of investigated delivery systems to improve ocular drug delivery. Some promising results of substances delivered to the retina suggest that topical treatment of retinal diseases might be possible in the future, which warrants further research.

The Emerging Role of Topical Ocular Drugs to Target the Posterior Eye

The prevalence of chronic fundus diseases is increasing with the aging of the general population. The treatment of these intraocular diseases relies on invasive drug delivery because of the globular structure and multiple barriers of the eye. Frequent intraocular injections bring heavy burdens to the medical care system and patients. The use of topical drugs to treat retinal diseases has always been an attractive solution. The fast development of new materials and technologies brings the possibility to develop innovative topical formulations. This article reviews anatomical and physiological barriers of the eye which affect the bioavailability of topical drugs. In addition, we summarize innovative topical formulations which enhance the permeability of drugs through the ocular surface and/or extend the drug retention time in the eye. This article also reviews the differences of eyes between different laboratory animals to address the translational challenges of preclinical models. The fast development of in vitro eye models may provide more tools to increase the clinical translationality of topical formulations for intraocular diseases. Clinical successes of topical formulations rely on continuous and collaborative efforts between different disciplines.

Numerical modeling of therapeutic lens drug delivery in the anterior human eye for the treatment of primary open-angle glaucoma

A numerical model of drug delivery from a therapeutic lens in the anterior portion of the human eye has been developed for a more effective treatment plan of primary open-angle glaucoma. The numerical model takes into account the drug diffusion through the therapeutic lens along with heat transfer and aqueous humor flow in different orientations of the human eye (supine (two-dimensional) as well as standing (three-dimensional)). Results illustrate that the drug diffuses through the therapeutic lens to the cornea and is convected into the anterior chamber of the eye due to the temperature gradient across the eye. In addition, eye orientation significantly affects drug delivery with supine orientation providing better and uniform drug exposure in different target regions of the eye as compared to standing in the case of the therapeutic lens. Furthermore, a comparison of the therapeutic efficacy of the therapeutic lens has been done with topical administration and the drug uptake results from both the drug delivery modes have been validated with the experimental data reported in the literature. The developed model may help ophthalmologists to comprehend the transport and retention of different drugs in different domains and orientations of the human eye when administered through a therapeutic lens.

Improving eye-drop administration skills of patients - A multicenter parallel-group cluster-randomized controlled trial

Background

Eye-drop administration errors occur in the majority of patients and increase the risk for treatment failure or systemic adverse events. While lacking knowledge is the principal error cause, most patients overestimate their skills and are unaware of often substantial knowledge gaps. Therefore, the impact of including motivational patient education on long-term eye-drop administration skills of patients was investigated.

Methods

This is a cluster-randomized controlled trial in German community pharmacies. Patient education in both groups comprised observation of the patient during eye-drop administration to identify individual errors, pharmaceutical counseling, and teach-back evaluation of the training. In the intervention group, motivational communication techniques were included to increase error awareness and readiness for patient education. In addition, intervention patients were trained on repeated errors until administration was performed correctly. In contrast, patients in the control group only received feedback on erroneous administration steps without another assessment and reinforced training.

Results

In total, 152 adult patients were eligible to the study and 91 patients (intervention group N = 46) agreed to participate in a 1-month, 6-month, and 12-month follow-up. Patient education significantly increased the proportion of patients correctly administering eye-drops from 6% (7 out of 56 intervention patients, 1 out of 82 control patients) at baseline to 35% (12 out of 30 intervention patients, 12 out of 39 control patients, p ≤ 0.001) at the 1-month follow-up, and 64% (11 out of 15 intervention patients, 17 out of 29 control patients, p ≤ 0.001) at the 6-month follow-up irrespective of group allocation. In some patients previously resolved errors recurred during follow-up visits. This emphasizes the need for periodical reevaluation of patient administration skills and the provision of prevention strategies besides education.

Conclusion

Patient education that included demonstration of administration skills and verbal and written counseling on observed errors improved eye-drop administration skills irrespective of the communication technique applied. Whereof, high drop-out rates limited the power to detect a difference between groups. In particular, periodic demonstration of administration skills seemed important for sustainable improvement of administration skills. However, further error prevention strategies such as additional education materials or support by a caregiver may be necessary in some patients.

Extended Release of Timolol from Ethyl Cellulose Microparticles Laden Hydrogel Contact Lenses

Glaucoma is a second leading cause of blindness globally after cataract, which is managed through eye drops, which are highly inefficient due to a low bioavailability of less than 1-5%. Frequent administration of eye drops leads to incompliance in patients, so there is a great need for medical device such as contact lenses to treat glaucoma. The objective of research was to provide sustained ocular delivery of timolol via prototype poly (hydroxyethyl methacrylate) hydrogel contact lenses which may improve bioavailability due to increase in ocular residence time of drug. The present work was to encapsulate drug in ethylcellulose microparticles, and to entrap these microparticles in the hydrogel. Microparticles were prepared by spray drying method using different ratios of drug to ethylcellulose. The solid state characterization studies of drug loaded microparticles revealed the transformation of drug to an amorphous state. The hydrogels were characterized by studying their optical and physical properties to determine their suitability as extended wear contact lenses. Microparticles laden hydrogels were compared with direct drug loaded hydrogels. The study of microparticles laden hydrogels showed reduction in optical and physical properties and the impact was proportional to the amount of microparticles in hydrogels. The results suggest the application of optimization and nanotechnology. In vitro drug release study revealed that direct loading batch delivers drug for 22 hours with high drug loading of 150 µg, while microparticles laden hydrogel deliver drug up to 48 hours (zero order kinetics) with low drug loading of 50 µg. The hydrogels appeared safe in the cytotoxicity study. The study demonstrated the promising potential of loading the ethyl cellulose microparticles into hydrogels to serve as a good platform for sustained ophthalmic drug delivery.

Extended release of timolol from nanoparticle-loaded fornix insert for glaucoma therapy

We have developed a cylindrical insert that can be inserted in the fornix for extended release of glaucoma drug timolol. The insert is prepared by incorporating timolol-loaded nanoparticles into a poly hydroxyl ethyl methacrylate (p-HEMA) matrix. A 1-mm diameter, 7.5-mm long insert with 25% (w/w) particles can release timolol for about 10 days at an average rate of about 15 μg/day, which may be therapeutically effective. The increase in particle fraction increases drug loading, but also increases the release duration. The net effect of increasing the particle fraction is a significant increase in release duration, but a decrease in daily drug release rates, in the first few weeks. The release duration increases to about 1 and 3 months on increasing the particle fraction to 50% and 75%, respectively. The average daily release rates in the first 3 weeks are 15, 9, and 3 μg/day for the inserts with 50%, 75%, and 100% (w/w) particles, respectively. The mechanism of release is hydrolysis of the ester bond that links timolol to the propoxylated glyceryl triacrylate matrix, and thus the release profiles fit a first order reaction model. The water content of the inserts decreases from 31% to almost zero on increasing the particle loading from 25% to 100%. The rate constant for the hydrolysis decreases with an increase in particle loading in the insert most likely due to the reduction in the water content. The inserts can be packaged in wet conditions and stored in a refrigerator, but the inserts will exhibit a burst release caused by release of the drug from the particles into the p-HEMA matrix during the shelf life. Also, the magnitude of drug release after the initial burst is reduced due to the storage. The burst effect could potentially be avoided by packaging the inserts in a dry state, with hydration before insertion.

Glaucoma Medications

As with many diseases, glaucoma increases in frequency in older populations, and is very often encountered in patients taking multiple medications. While the exact mechanism of glaucomatous optic neuropathy (GON) is not known, intraocular pressure (IOP) is thought to be central to the process, and reducing IOP is the only known effective treatment. The newer definition of glaucoma is an IOP-sensitive optic neuropathy. While large, controlled studies have indicated that reducing IOP will slow the progression of disease, the contributions of other conditions and medications have not been adequately studied. As the adverse effect profiles of medical therapies for glaucoma have improved, use of these agents has increased greatly. This has resulted in a large number of older patients taking glaucoma medications. Since topical medications can easily be overlooked in a medical history, and are for the most part well tolerated, systemic complications from these agents can be missed. In addition to being a common disease requiring treatment, glaucoma is also a model system for other degenerative diseases, and many of the concepts originally developed in relation to neurodegenerative diseases such as Alzheimer's disease are under investigation for glaucoma. These include approaches targeted towards neuroprotection and excitotoxicity.

Reducing intraocular pressure: is surgery better than drugs?

Reducing IOP is presently the evidence based, most accepted and most practised therapeutical approach for glaucoma patients. Currently topical ocular hypotensive medications, with its different classes, as well as filtering surgery (trabeculectomy and non-penetrating glaucoma surgery) are in the forefront of therapeutic modalities for IOP reduction. This article looks at the potential advantages and disadvantages of topical medications versus filtering surgery. It does not directly address the question of initial treatment of glaucoma, or what is the better treatment of glaucoma, as other review articles had, but rather looks in a more specific on the pros and the cons of each in relation to IOP reduction. In other words this article deals with the situation once the decision has been made to reduce IOP.

Determinants of eye drop size

Ophthalmic solutions are available for multidose or single-dose administration in a wide variety of glass and plastic dropper bottles which deliver drops with a volume between 25 and 70 microl. From a biopharmaceutical and economic point of view, however, smaller volumes of 5 to 15 microl should be instilled. In this review, the technical, pharmaceutical, and therapeutic aspects of eye drop formation and delivery are presented. The different types of containers are described and the determinants of eye drop size are discussed, such as the design and physical characteristics of the dropper tip and bottle, the physico-chemical properties of the solution, and the manner in which the patient dispenses the drops. Preferred and alternative instillation techniques and aids to facilitate the administration of eye drops by elderly patients are described.

Influence of emulsion droplet surface charge on indomethacin ocular tissue distribution

The aim of this study was to compare the corneal penetration of indomethacin from Indocollyre [a marketed hydro-poly(ethylene glycol) (PEG) ocular solution] to that of a negatively and a positively charged submicron emulsion. Male albino rabbits were separated randomly into three groups and each group (N = 15) was treated with either one drop of radiolabeled 0.1% Indocollyre, or 0.1% indomethacin positively or negatively charged submicron emulsion, respectively. The rabbits were sacrificed at selected time points and the eyes were enucleated. The eyes were dissected into the different tissues: cornea, conjunctiva, aqueous humor, iris, lens, vitreous, sclera, and retina. The samples were weighed before radioactivity counting. Regardless of the preparation instilled, the highest concentration of indomethacin was achieved in the cornea followed by conjunctiva, sclera retina, and aqueous humor. However, the positively charged emulsion provided significantly higher drug levels than the control solution and negatively charged emulsion only in the aqueous humor and sclera-retina. Furthermore, the spreading coefficient of the positively charged emulsion on cornea is four times higher than that of the negatively charged emulsion. It was therefore deduced that the positively charged submicron emulsions have better wettability properties on the cornea compared to either saline or the negatively charged emulsion. The positive charge may prolong the residence time of the drop on the epithelial layer of the cornea and thus enable better drug penetration through the cornea to the internal tissues of the eye, as confirmed by the animal studies.

Efficacy and tolerability of timolol maleate ophthalmic gel-forming solution versus timolol ophthalmic solution in adults with open-angle glaucoma or ocular hypertension: a six-month, double-masked, multicenter study

BACKGROUND

Timolol has been formulated in a highly purified gellan gum to improve its duration of action. The efficacy of this formulation in short-term studies using once-daily dosing has been reported.

OBJECTIVE

The purpose of this study was to evaluate the efficacy and tolerability of 0.5% timolol maleate ophthalmic gel-forming solution (timolol GS) given once daily versus 0.5% timolol solution given twice daily in a long-term trial.

METHODS

This was a multicenter, double-masked, 6-month trial. After a washout of ocular hypotensive medication, 286 patients with open-angle glaucoma or ocular hypertension were randomly assigned in a 2:1 ratio to receive 0.5% timolol GS in both eyes once daily or 0.5% timolol solution in both eyes twice daily. All patients received a morning (9 AM) and evening (9 PM) dose. For patients in the timolol GS group, the evening dose consisted of a vehicle only, whereas for patients in the timolol solution group, both doses consisted of active drug. Intraocular pressure (IOP) was measured at trough (before morning instillation) and peak (2 hours after instillation) at follow-up examinations at weeks 2, 4, 8, 12, and 24. Adverse events were monitored using patient reports.

RESULTS

Of the 286 patients randomized, 191 received timolol GS and 95 received timolol solution. Ninety-three percent of patients (265/286) completed the study. At the end of the treatment interval (week 24), the mean decrease in IOP at trough ranged from 5.6 to 5.9 mm Hg in the timolol GS group and from 6.3 to 6.6 mm Hg in the timolol solution group. Similar efficacy was observed at 11 AM (peak). At week 24, the difference in mean IOP between treatments was -0.61 mm Hg (95% CI -1.44 to 0.22) at trough and -0.79 mm Hg (95% CI -1.77 to 0.20) at peak, indicating no significant difference between the 2 timolol formulations. The number of reports of blurred vision and tearing was significantly higher in the timolol GS group than in the timolol solution group (P = 0.04), whereas burning/stinging was reported more frequently in the timolol solution group than in the timolol GS group (P = 0.04). At week 12, the decrease in mean heart rate at trough (hour 0) was significantly less for patients in the timolol GS group than for those in the timolol solution group (-1.1 vs -4.2 bpm; P = 0.024). At week 24 (hour 0), the decrease in mean heart rate was less for patients treated with timolol GS by 2.5 bpm (P = 0.051). The heart rate data at peak (hour 2) was similar to that observed at trough at week 12 (-2.7 vs -5.7 bpm; P = 0.006) and week 24 (-3.1 vs -4.7 bpm; P = 0.063). The mean change in blood pressure was not significantly different between treatments. There were no clinically significant differences between the groups in visual acuity, biomicroscopy and ophthalmoscopy results, or visual fields.

CONCLUSIONS

Timolol 0.5% GS administered once daily was shown to be as effective in lowering IOP as the equivalent concentration of timolol 0.5% solution administered twice daily in patients with ocular hypertension or open-angle glaucoma.

The evolving pharmacotherapeutic profile of brimonidine, an alpha 2-adrenergic agonist, after four years of continuous use

Since its introduction in 1996, use of brimonidine tartrate 0.2% ophthalmic solution (Alphagan, Allergan), a highly selective alpha 2-adrenergic agonist, has become increasingly popular for the initial and long-term management of ocular hypertension and glaucoma. Recently, ongoing clinical comparison trials of up to three years in length have reported sustained intraocular pressure (IOP) lowering efficacy with brimonidine 0.2% b.i.d., which was comparable with timolol 0.5% (Timoptic; Merck & Co.), accompanied by a favourable tolerability and safety profile. Also, many post-market studies have demonstrated the utility of brimonidine 0.2% b.i.d. as mono- and adjunctive therapy. Furthermore, major inroads have been made in the study of other possible pharmacotherapeutic benefits of brimonidine treatment, namely the potential for neuroprotection. This review will present a brief developmental history and examine key pharmacotherapeutic characteristics of brimonidine, including its receptor selectivity, IOP-lowering mechanism of action and potential neuroprotective activities. Moreover, the literature on brimonidine's efficacy and safety profiles in the treatment of ocular hypertension and glaucoma will be perused, and new four-year data from an ongoing double-masked clinical study comparing brimonidine tartrate 0.2% with timolol 0.5%, b.i.d. will be introduced. Brimonidine 0.2% b.i.d. provided sustained IOP-lowering efficacy comparable to timolol 0.5% b.i.d., with no significant differences at trough or peak during year four of continuous use. Visual fields were well preserved in both treatment groups with 93% of brimonidine patients and 91% of timolol patients showing no change or improvement. Brimonidine continued to appear safe and well-tolerated, with no clinically significant effects on mean heart rate or blood pressure, and no serious drug-related adverse events (AEs). Two out of 36 brimonidine patients developed ocular allergy; both were resolved without sequelae. Overall post-market surveillance found no reports of unexpected or serious drug-related AEs. These long-term results, in conjunction with those reported in the literature, suggest that brimonidine 0.2% b.i.d. is a highly appropriate first- and second-line therapy for long-term management of glaucoma and ocular hypertension. Potential neuroprotective effects of brimonidine therapy, which might provide additional vision sparing benefit, although supported by compelling animal studies, await clinical verification.

Antiglaucoma medications: a review of safety and tolerability issues related to their use

BACKGROUND

Much experience has been gained with the use of older classes of antiglaucoma agents--topical beta-adrenergic-receptor antagonists, nonselective adrenergic-receptor agonists, oral carbonic anhydrase inhibitors, and cholinergic agents. In the past decade, new drugs and classes of drugs used to treat glaucoma have become available, including topical carbonic anhydrase inhibitors, prostaglandin analogues, and alpha2-adrenergic-receptor agonists. Extensive community-based use of antiglaucoma medications has led to an increased understanding of the acute and long-term safety and tolerability issues associated with their use.

OBJECTIVE

This paper reviews the side effects associated with the various classes of topical antiglaucoma drugs, with a particular focus on long-term safety issues.

Systemic effects of topical ophthalmic beta-adrenoceptor antagonists

Topical ophthalmic beta-adrenoceptor antagonists (beta-blockers) are generally recognized as the treatment of choice in glaucoma management due to favourable efficacy, safety and tolerability. Despite topical ocular administration, beta-blockers are systemically absorbed, in relatively small amounts, through the nasolacrimal drainage system and can adversely affect cardiovascular and pulmonary function. While cardioselective beta-blockers, such as betaxolol, possibly confer an advantage with respect to clinical safety through their receptor affinity, systemic effects are also influenced by other pharmacological factors, including the rate and extent of systemic absorption and the extent of plasma protein binding. These factors are reviewed to distinguish the various ophthalmic beta-blockers and to explain the observed clinical differences in the safety profiles of these medications.

The influence of penetration enhancers on the volume instilled of eye drops

The influence of the physicochemical properties of various penetration enhancers on the weight of drops dispensed from flexible plastic dropper bottles was examined. Two dropper tips with a different design were compared and the dropper bottle was held in the upright position (90 degrees angle) or at a 45 degrees angle. These two angles were chosen to simulate the manipulation of an eye dropper bottle by the patient. The surface tension of the penetration enhancer solutions was determined using the dynamic drop volume method. The dynamic surface tension values ranged from 65 to 30 mN/m. The lower the surface tension of the solution, the lower the weight of the drop delivered. Both the design of the dropper tip and the manipulation technique of the dropper bottle had a moderate to important influence on the drop weight. The relationship between the surface tension of the penetration enhancer solution instilled and the comfort of the patient was evaluated by an acceptability test based on answering a questionnaire. Penetration enhancers can be used to reduce the drop size of conventional ophthalmic solutions on condition that they do not elicit local irritation.

Randomised, controlled trial of spirometric changes in elderly people receiving timolol or betaxolol as initial treatment for glaucoma

AIM

To investigate respiratory and cardiovascular side effects in elderly people in the first 12 months after commencing topical beta antagonists.

METHODS

40 patients (mean age 74 years) were recruited to a randomised, masked study. Spirometry, pulse, and blood pressure were recorded before, 1 month, and 12 months after starting topical therapy with either timolol 0.5% twice daily or betaxolol 0.5% twice daily.

RESULTS

After 1 month five of 20 patients allocated timolol and three of 20 given betaxolol had discontinued it for respiratory reasons, not always accompanied by symptoms. There were no significant differences in changes in mean values of spirometry, pulse, or blood pressure between groups. No further changes were made in therapy for respiratory reasons in the following year. One patient suffered a hypotensive stroke within 2 days of starting timolol.

CONCLUSIONS

By performing spirometry before starting topical beta antagonist therapy and repeating it after 1 month most patients at risk of respiratory impairment can be identified.

Cardiac failure aggravated by timolol eye drops: preoperative improvement by changing to pilocarpine

A 73-year-old woman with cardiac dysfunction had several episodes of severe bradycardia and pulmonary oedema when waiting for peripheral vascular surgery. She used timolol eye drops for primary open-angle glaucoma. The first episode of pulmonary oedema occurred two weeks prior to and the second on the day before the planned surgery. There were another two episodes of pulmonary oedema before she was transferred to the Department of Internal Medicine where she had a further two episodes of cardiac failure. After changing timolol to pilocarpine eye drops, the patient's condition was stabilized, and two weeks later surgery and postoperative recovery were uneventful.

Minimizing systemic absorption of topically administered ophthalmic drugs

Due to absorption several ocularly applied medications give rise to systemic side-effects. The problem of systemic drug absorption should be taken into account in designing ocular drug and dosage forms so that oculospecificity of the medications is optimized. In this review we summarize the current knowledge about the systemic absorption of ocularly applied topical drugs. Special emphasis is directed to the methods that can be used to minimize systemic absorption and increase the oculospecificity of drugs, e.g., reducing volume and increasing viscosity of eyedrops, controlling drug release from depot preparations, prodrug-derivatization, and addition of vasoconstrictive agents.

Cardiac effects of different eyedrop preparations of timolol in rabbits

Coadministration of phenylephrine and increasing solution viscosity can decrease systemic timolol absorption after eyedrop application. In this study, changes in the heart rate of rabbits after non-viscous (1 cP) and viscous timolol-phenylephrine (330 cP) solution were compared with those after control timolol eyedrops. The resting heart rate of rabbits was not influenced by control timolol eyedrops (0.6 mg/ml, 25 microliters in both eyes). In contrast, control timolol eyedrops antagonized greatly isoproterenol-induced tachycardia for 120 min. Timolol (0.6 mg/ml)-phenylephrine (0.8 mg/ml) eyedrops (25 microliters in both eyes) antagonized the chronotropic effect of isoproterenol less than control timolol eyedrops for the first 10 min. Compared to control timolol eyedrops, administration of viscous timolol (0.3 mg/ml)-phenylephrine (0.8 mg/ml) solution (25 microliters in both eyes) lowered systemic beta-blocking activity of timolol for 120 min. Previously we have shown that compared to non-viscous (1 cP) timolol (5.0 mg/ml) eyedrop (25 microliters), viscous (330 cP) timolol (2.5 mg/ml)-phenylephrine (0.8 mg/ml) solution (25 microliters) results in equal or increased timolol concentrations in the ocular tissues. All three timolol eyedrops antagonized the isoproterenol-induced tachycardia more than buffer solution but the onset of significant beta-blocking effect induced by eyedrops varied from 3 min (control eyedrop) to 40 min (viscous eyedrop). Our results indicate that possible cardiac effects of ophthalmic timolol can be diminished by phenylephrine coadministration and increased solution viscosity.

Development of D-timolol for the treatment of glaucoma and ocular hypertension

It has been found that D-timolol is equipotent or slightly less potent than L-timolol to lower the intraocular pressure (IOP) in normotensive rabbits, water loaded ocular hypertensive rabbits, alpha-chymotrypsin induced glaucoma rabbits, hypertonic saline infused IOP recovery model of rabbits, normotensive human volunteers, glaucoma patients and ocular hypertensive human individuals. Although L-timolol has been used widely for the treatment of glaucoma and ocular hypertension, it produces numerous side effects including cardiovascular disturbances, asthmatic attack, psychological depression, etc. Since D-timolol has much weaker affinity toward beta-adrenergic receptors, it was found to have 1/80-1/300 the beta-adrenergic blocking potency of L-timolol to block beta-adrenergic receptors in guinea pig tracheal preparations and 1/90 of L-timolol to block beta-adrenergic receptors in guinea pig atrial preparations. As a result, D-timolol showed no subjective nor objective side effects on pupil size, conjunctiva, cornea, blood pressure and pulse rate. Further, D-timolol was reported to increase retinal and choroid blood flow in rabbits without affecting overall ocular blood flow. On the contrary, L-timolol was found to significantly reduce the overall ocular blood flow and retinal and choroid blood flows in rabbits, although it might slightly increase the retinal blood flow in normotensive individuals. D-Timolol was well absorbed across the cornea as L-timolol and produced the duration of action as long as L-timolol. These results indicate that D-timolol could be a better agent than L-timolol for the treatment of glaucoma and ocular hypertension.

Effects of D-timolol and L-timolol on ocular blood flow and intraocular pressure

Effects of D-timolol and L-timolol on IOP were compared with two rabbit models. When the drug solution was injected into vortex vein, 1% D-timolol produced ocular hypotension just like 0.5% L-timolol except D-timolol was less potent than L-timolol to lower the IOP. On the other hand, when 0.5% of D-timolol and L-timolol were instilled into the rabbit eye on IOP recovery model both agents showed equipotency to delayed the IOP recovery. Effects of D-timolol and L-timolol on ocular blood flow were also studied with two rabbit models. D-Timolol at 0.5% did not affect the ocular pulsatile blood flow measured with Langham's pneumatonometer whereas 0.5% L-timolol significantly suppressed it. D-Timolol (0.5%) was found to increase retinal and choroidal blood flows measured with laser Doppler method whereas L-timolol suppressed it. These results indicate that D-timolol though less potent than L-timolol to lower IOP, is superior over L-timolol to improve the blood flow in retina and choroid.

Levobunolol and betaxolol. A double-masked controlled comparison of efficacy and safety in patients with elevated intraocular pressure

In a double-masked, randomized, controlled clinical trial, the authors evaluated the ocular hypotensive efficacy of twice-daily treatment with levobunolol (0.25 and 0.5%) and betaxolol (0.5%) in 85 patients with open-angle glaucoma or ocular hypertension. During the 3-month study, intraocular pressure (IOP) reductions in the two levobunolol groups were significantly greater than in the betaxolol group. From a mean baseline IOP of approximately 25 mmHg, overall mean reductions were 6.2 and 6.0 mmHg for the 0.25 and 0.5% levobunolol groups, respectively, and 3.7 mmHg for the betaxolol group. No clinically or statistically significant among-group differences were noted in the systemic safety variables evaluated. These data suggest that although all three treatments are effective, levobunolol provides a greater reduction in IOP than betaxolol.