Ocular betaxolol. A review of its pharmacological properties, and therapeutic efficacy in glaucoma and ocular hypertension

Different concentrations of betaxolol switch cell fate between necroptosis, apoptosis, and senescence in human corneal stromal cells

Betaxolol is commonly used to manage glaucoma in clinical practice. However, its long-term use may damage the cornea. Thus, the cytotoxicity and mechanisms of betaxolol in human corneal stromal cells (HCSCs) warrant further study. In this study, we used in vitro HCSCs and in vivo rabbit corneal models to investigate betaxolol cytotoxic effects and mechanism of action. At near-clinical concentrations (0.28% and 0.14%), betaxolol inhibited caspase-8 activity, activated receptor-interacting protein kinase (RIPK)1, RIPK3, and mixed-spectrum kinase-like domain (MLKL), and phosphorylated MLKL to induce necroptosis in HCSCs. Similarly, moderate concentrations of betaxolol (0.07%-0.0175%) activated caspase-8 to trigger the exogenous apoptotic pathway. Through the intrinsic apoptotic pathway, betaxolol upregulated the expression of Bcl-2 family apoptotic proteins Bax and Bad and downregulated that of anti-apoptotic proteins Bcl-2 and Bcl-xL. This subsequently disrupted the mitochondrial membrane potential and cytoplasmic transfer of cytochrome c and apoptosis-inducing factor, activated caspase-9, and induced apoptosis in HCSCs. Furthermore, continuous treatment with low betaxolol concentrations (0.00875%) for three generations of HCSCs prevented apoptosis by promoting the expression of Bcl-xL and suppressing that of Bax. However, its toxic effects initiated cellular senescence by increasing reactive oxygen species, leading to the disruption of energy metabolism and DNA damage. Finally, clinical concentrations of betaxolol had a pro-apoptotic effect on rabbit corneal stromal cells in vivo. These results suggest that betaxolol induces cytotoxicity in a concentration-dependent manner in HCSCs, and that caspase-8 and Bcl-2 family proteins may be critical switches in the conversion of different HCSC death mechanisms.

Pharmaceutical In Situ Gel for Glaucoma: Recent Trends and Development with an Update on Research and Patents

Glaucoma is a progressive visual polyneuropathy characterized by retinal ganglion cell atrophy and optic nerve head changes. It's generally triggered due to increased intraocular pressure compared with the healthy eye. Glaucoma is treated with various medications in traditional eye drops, such as prostaglandins, carbonic anhydrase inhibitors, beta-blockers, and others. Such treatments are difficult to use and produce lachrymal leakage and inadequate corneal permeability, resulting in lower availability. Ophthalmic in situ gels, introduced in past decades with tremendous effort, are among the finest various choices to solve the drawbacks of eye drops. Employing different polymers with pH-triggered, temperature-triggered, and ion-activated processes have been used to generate ophthalmic in situ gelling treatments. Once those preparations are delivered into the eye, they change phase from sol to gel, allowing the medicine to stay in the eye for longer. These formulations are known as smart gels as they turn into gelling fluids when administered into the eyes. The different mechanisms of in situ gel formulations are used for the management of glaucoma and are discussed in this review article.

Design, Characterization and Pharmacokinetic-Pharmacodynamic Evaluation of Poloxamer and Kappa-Carrageenan-Based Dual-Responsive In Situ Gel of Nebivolol for Treatment of Open-Angle Glaucoma

This study developed a dual-responsive in situ gel of nebivolol (NEB), a selective β-adrenergic antagonist. The gel could achieve sustained concentrations in the aqueous humor to effectively treat glaucoma. The gel was prepared using a combination of poloxamers (Poloxamer-407 (P407) and Poloxamer-188 (P188)) and kappa-carrageenan (κCRG) as thermo-responsive and ion-sensitive polymers, respectively. Box-Behnken design (BBD) was used to optimize the effect of three critical formulation factors (concentration of P407, P188 and κCRG) on two critical response variables (sol-to-gel transition temperature of 33-35 °C and minimum solution state viscosity) of the in situ gel. A desirability function was employed to find the optimal concentrations of P407, P188 and κCRG that yielded a gel with the desired sol-to-gel transition temperature and solution state viscosity. An NEB-loaded gel was prepared using the optimized conditions and evaluated for in vitro drug release properties and ex vivo ocular irritation studies. Furthermore, ocular pharmacokinetic and pharmacodynamics studies were conducted in rabbits for the optimized formulation. The optimized NEB-loaded gel containing P407, P188 and κCRG had a sol-to-gel transition temperature of 34 °C and exhibited minimum viscosity (212 ± 2 cP at 25 °C). The optimized NEB-loaded gel sustained drug release with 86% drug release at the end of 24 h. The optimized formulation was well tolerated in the eye. Ocular pharmacokinetic studies revealed that the optimized in situ gel resulted in higher concentrations of NEB in aqueous humor compared to the NEB suspension. The aqueous humor C_max of the optimized in situ gel (35.14 ± 2.25 ng/mL) was 1.2 fold higher than that of the NEB suspension (28.2 ± 3.1 ng/mL), while the AUC_0-∞ of the optimized in situ gel (381.8 ± 18.32 ng/mL*h) was 2 fold higher than that of the NEB suspension (194.9 ± 12.17 ng/mL*h). The systemic exposure of NEB was significantly reduced for the optimized in situ gel, with a 2.7-fold reduction in the plasma C_max and a 4.1-fold reduction in the plasma AUC_0-∞ compared with the NEB suspension. The optimized gel produced a higher and sustained reduction in the intra-ocular pressure compared with the NEB suspension. The optimized gel was more effective in treating glaucoma than the NEB suspension due to its mucoadhesive properties, sustained drug release and reduced drug loss. Lower systemic exposure of the optimized gel indicates that the systemic side effects can be significantly reduced compared to the NEB suspension, particularly in the long-term management of glaucoma.

Emerging drugs for the treatment of glaucoma: a review of phase II & III trials

INTRODUCTION

Glaucoma is a progressive optic neuropathy and the leading cause of irreversible vision loss. By 2040, the number of individuals with glaucoma is expected to nearly double. The only known modifiable risk factor for glaucoma is intraocular pressure. Topical medications are often used as first-line therapies. Although there are numerous available treatments, there continues to be a need for the development of new medical therapies due to variable response, intolerable side-effect profiles in some patients, and elevated intraocular pressure refractory to other treatments.

AREAS COVERED

This review will cover glaucoma medications currently undergoing phase II and III of drug development.

EXPERT OPINION

There are numerous drugs currently in development that have demonstrated significant and clinically relevant reduction of intraocular pressure. Differentiating factors include improved tolerability, novel mechanisms of action, multiple mechanisms of action, or superior IOP reduction. However, the availability of generic prostaglandin analogs may limit adoption of these novel compounds as first-line agents, except for certain subgroups of glaucoma patients. Use as adjuvant or second-line therapy appears more likely for the majority of glaucoma patients.

'Ab Ovo' Chiral Phases and Chiral Reagents for Liquid Chromatographic Separation and Isolation of Enantiomers

The de-novo approach of mixing chirally pure reagents or Cu(II)-L-amino acid complexes in the slurry of silica gel for preparing TLC plates was reported from author's laboratory and was successful for separation and isolation of enantiomers. Using high molar absorptivity molecules, e. g., 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, more than 38 new chiral derivatizing reagents were synthesized in our laboratory by straightforward nucleophilic substitution with simple chiral auxiliaries. Besides, (S)-naproxen, (S)-ketoprofen, and (S)-levofloxacin were used as chiral platforms. A conceptual approach using both achiral phases in chromatography for enantioseparation was also adopted. ¹ H NMR and DFT based software were used to explain structures of non-covalent and covalent diastereomeric pairs and determination of configuration and separation mechanism. The methods can be easily used to determine and control enantiomeric purity with advantages over a variety of commercial chiral phases.

Wettability and contact angle affect precorneal retention and pharmacodynamic behavior of microspheres

In the present study, we describe the development of betaxolol hydrochloride and montmorillonite with ion exchange in a single formulation to create a novel micro-interactive dual-functioning sustained-release delivery system (MIDFDS) for the treatment of glaucoma. Betaxolol hydrochloride molecule was loaded onto the montmorillonite by ion exchange and MIDFDS formation was confirmed by XPS data. MIDFDS showed similar physicochemical properties to those of Betoptic, such as particle size, pH, osmotic pressure, and rheological properties. Nevertheless, the microdialysis and intraocular pressure test revealed better in vivo performance of MIDFDS, such as pharmacokinetics and pharmacodynamics. With regards to wettability, MIDFDS had a larger contact angle (54.66 ± 5.35°) than Betoptic (36.68 ± 1.77°), enabling the MIDFDS (2.93 s) to spread slower on the cornea than Betoptic (2.50 s). Moderate spreading behavior and oppositely charged electrostatic micro-interactions had a comprehensive influence on micro-interactions with the tear film residue, resulting in a longer precorneal retention time. Furthermore, MIDFDS had a significant sustained-release effect, with complete release near the cornea. The dual-functioning sustained-release carrier together with prolonged pre-corneal retention time (80 min) provided sufficiently high drug concentrations in the aqueous humor to achieve a more stable and long-term IOP reduction for 10 h. In addition, cytotoxicity and hemolysis tests showed that MIDFDS had better biocompatibility than Betoptic. The dual-functioning microspheres presented in this study provide the possibility for improved compliance due to low cytotoxicity and hemolysis, which suggests promising clinical implications.

Systemic side effects of glaucoma medications

Glaucoma is a progressive loss of retinal ganglion cells leading to visual field loss. Lowering intraocular pressure is currently the only modifiable risk factor to slow glaucoma progression. Intraocular pressure-lowering options include topical and systemic medications, lasers, and surgical procedures. Glaucoma eye drops play a major role in treating this blinding disease. Similar to all medications, the glaucoma medications have their own adverse effects. The majority of glaucoma medications work by stimulating or inhibiting adrenergic, cholinergic, and prostaglandin receptors, which are distributed all over the body. Therefore, the glaucoma medications can affect organs other than the eye. This review will discuss the systemic adverse effects of carbonic anhydrase inhibitors, sympathomimetics, para-sympathomimetics, beta blockers, prostaglandin analogs, hyperosmotic agents, and novel glaucoma medications with a stress on pregnant patients, breastfeeding mothers, and paediatric patients.

Betaxolol: A comprehensive profile

Betaxolol is a relatively cardioselective β-adrenoceptor blocking drug, with no partial agonist (intrinsic sympathomimetic) activity and weak membrane-stabilizing (local anesthetic) activity. Betaxolol selectively and competitively binds to and blocks beta-1 (β1) adrenergic receptors in the heart, thereby decreasing cardiac contractility and rate. This leads to a reduction in cardiac output and lowers blood pressure. When applied topically in the eye, this agent reduces aqueous humor secretion and lowers the intraocular pressure (IOP). In addition, betaxolol prevents the release of renin, a hormone secreted by the kidneys that causes constriction of blood vessels. Betaxolol (S)-(-)-enantiomer shows higher pharmacological activity. This chapter provides a complete review of nomenclature, physiochemical properties, methods of preparation, identification techniques and various qualitative and quantitative analytical techniques as well as pharmacology of betaxolol. In addition, the chapter also includes review of several methods for enantiomeric separation betaxolol using chromatographic techniques.

Cardiovascular and respiratory considerations with pharmacotherapy of glaucoma and ocular hypertension

Glaucoma and ocular hypertension are highly prevalent conditions in individuals over the age of 40 and are commonly seen together in patients with cardiovascular disease. Many of the antiglaucoma medications, when systemically absorbed, affect the sympathetic and parasympathetic nervous systems of patients and can cause cardiovascular toxicity. Such adverse effects are frequently associated with the long-term use of potentially toxic agents in elderly people, who are most prone to chronic eye disease. Moreover, patients may not associate their symptoms with the topical eye medications, and consequently may not report adverse drug effects. Drug-drug interactions can also occur when patients are taking medications for both cardiovascular disease and glaucoma. In this review, the systemic toxicity of these agents is reviewed, along with possible drug-drug interactions. Mention is made of other antiglaucoma medications used alone and in combination with topical beta-blockers. Identification of genetic loci-a bold new step toward glaucoma treatment-is mentioned briefly at the end of the article.

Acute effects of glaucoma medications on rat intraocular pressure

The rat has been used increasingly in glaucoma research, but many aspects regarding the regulation of its intraocular pressure (IOP) are still unknown. For example, it is not clear whether glaucoma medications can lower IOP in the rat similarly to human. This information will be valuable in evaluating this animal model for its usefulness in predicting drug effects in patients. Hence, we tested the acute IOP effects of selected glaucoma drugs topical administered onto the rat eye. In these studies, IOP was measured using the Tono-Pen XL tonometer. After a correlation between the IOP reported by the Tono-Pen and actual IOP was established, IOP measurements were obtained in slightly sedated adult rats. Effects of glaucoma medications were tested in two groups of animals. One group (12 h/L) was housed in a 12-h/12-h light/dark cycle. The other (24 h/L) was housed under constant light. Exposure of the animals to constant light increased their basal IOP from 20.5+/-0.6 mmHg (mean+/-S.E.M., n=12) to 32.0+/-0.5 mmHg. At 3 h after topical administration, Betoptic S lowered IOP by 4.3+/-1.7 mmHg (n=6) and 3.7+/-0.3 mmHg (n=6) in the 12 and 24h/L rats, respectively. Pilocarpine did not affect rat IOP. Xalatan produced a biphasic response in the rat. At 3h after topical administration, it increased IOP by 7.9+/-1.4 and 7.0+/-1.0 mmHg in the 12 and 24 h/L rats, respectively. By the next day, it decreased IOP by 3.0+/-1.0 and 6.0+/-0.8 mmHg in the 12 and 24 h/L rats, respectively. The IOP-enhancing effect of Xalatan was dose-dependent. The present study indicates that IOP responses of the rat to different pharmacological agents are not identical to those of the human. In the rat, Betoptic S, but not pilocarpine, lowered IOP. Xalatan initially increased then decreased IOP.

Effects of commercial antiglaucoma drugs to glutamate-induced [Ca2+)]i increase in cultured neuroblastoma cells

Over releasing of glutamate and cellular calcium influx always results in neuronal death. In the present study, we investigated various commercial antiglaucoma drugs including timolol (0.58 microM to 58 microM), betaxolol (1.62 microM to 162 microM), carteolol (6.8 microM to 680 microM), pilocarpine (4.08 microM to 408 microM), latanoprost (0.01 microM to 1.1 microM), dorzolamide (6.16 microM to 616 microM), brinzolamide (2.6 microM to 260 microM), brimonidine (0.68 microM to 68 microM), dipivefrin (0.28 microM to 28 microM) and preservative benzalkonium chloride on their effects to inhibit glutamate-induced intracellular free Ca(2+) ([Ca(2+)](i)) increase in cultured N1E-115 neuroblastoma cells. These drugs were diluted from original concentrations to 1/100, 1/1000 and 1/10000. The [Ca(2+)](i) mobility was studied after loading with fura-2-AM and analyzed by spectrofluorometry. It was found that betaxolol, dipivefrin and brimonidine have remarkable effects not only to inhibit the glutamate-induced [Ca(2+)](i) increase but also to decrease the basal [Ca(2+)](i). In the case of other drugs, only high concentration of timolol (58 microM) exhibited significant effect to completely prevent glutamate-induced [Ca(2+)](i) increase. Moreover, benzalkonium chloride did not exhibit any inhibitive effect. These results indicate that betaxolol, dipivefrin and brimonidine may have neuroprotective effects to inhibit the glutamate-induced over Ca(2+) influx damage.

Cardiovascular considerations in using topical, oral, and intravenous drugs for the treatment of glaucoma and ocular hypertension: focus on beta-adrenergic blockade

Glaucoma and ocular hypertension are highly prevalent conditions in individuals over the age of 40 and are commonly seen together in patients with cardiovascular disease. Many of the antiglaucoma medications, when systemically absorbed, affect the sympathetic and parasympathetic nervous systems of patients and can cause cardiovascular toxicity. Such adverse effects are frequently associated with the long-term use of potentially toxic agents in elderly people, who are most prone to chronic eye disease. Moreover, patients may not associate their symptoms with the topical eye medications, and consequently may not report adverse drug effects. Drug-drug interactions can also occur when patients are taking medications for both cardiovascular disease and glaucoma. This review focuses on beta-adrenergic blockers as topical antiglaucoma medications and other topical antiglaucoma drugs. The systemic toxicity of these agents is reviewed, along with the possible drug interactions. Brief mention is also made of other antiglaucoma medications used alone and in combination with topical beta-blockers.

Assessment of systemic adverse reactions induced by ophthalmic beta-adrenergic receptor antagonists

To assess quantitatively the risks of ophthalmic beta-blocking agents for cardiovascular and respiratory adverse reactions, we analyzed the binding kinetics of beta-blocking agents to the beta-1 and beta-2 adrenoceptors. The relationship between the occupancies for beta-1 and beta-2 adrenoceptors and the effects on the exercise pulse rate or the forced expiratory volume in one second (FEV1) after topical administration of carteolol, befunolol, timolol and betaxolol was analyzed using a ternary complex model. The beta-1 and beta-2 receptor occupancies after ophthalmic administration were calculated to be quite high as well as those after oral administration. The maximum occupancies for beta-1 and beta-2 receptors after ordinary ophthalmic administration were 52% and 88% for carteolol, 52% and 61% for befunolol, 62% and 82% for timolol, and 44% and 3% for betaxolol, respectively. Concave relationships were obtained between a decrease in exercise pulse rate and the beta-1 receptor occupancy and between a decrease in FEV1 and beta-2 receptor occupancy, respectively. Nasolacrimal occlusion was estimated to decrease the exercise pulse rate and FEV1 by 65% and 50%, respectively. The beta-1 and beta-2 adrenoceptor occupancies were proved to be the most appropriate indicators for cardiac and pulmonary adverse reactions evoked by ophthalmic beta-blocking agents.

Betaxolol, a beta(1)-adrenoceptor antagonist, reduces Na(+) influx into cortical synaptosomes by direct interaction with Na(+) channels: comparison with other beta-adrenoceptor antagonists

Betaxolol, a beta(1)-adrenoceptor antagonist used for the treatment of glaucoma, is known to be neuroprotective in paradigms of ischaemia/excitotoxicity. In this study, we examined whether betaxolol and other beta-adrenoceptor antagonists interact directly with neurotoxin binding to sites 1 and 2 of the voltage-sensitive sodium channel (Na(+) channel) in rat cerebrocortical synaptosomes. Betaxolol inhibited specific [(3)H]-batrachotoxinin-A 20-alpha-benzoate ([(3)H]-BTX-B) binding to neurotoxin site 2 in a concentration-dependent manner with an IC(50) value of 9.8 microM. Comparison of all the beta-adrenoceptor antagonists tested revealed a potency order of propranolol>betaxolol approximately levobetaxolol>levobunolol approximately carteolol>/=timolol>atenolol. None of the drugs caused a significant inhibition of [(3)H]-saxitoxin binding to neurotoxin receptor site 1, even at concentrations as high as 250 microM. Saturation experiments showed that betaxolol increased the K(D) of [(3)H]-BTX-B binding but had no effect on the B(max). The association kinetics of [(3)H]-BTX-B were unaffected by betaxolol, but the drug significantly accelerated the dissociation rate of the radioligand. These findings argue for a competitive, indirect, allosteric mode of inhibition of [(3)H]-BTX-B binding by betaxolol. Betaxolol inhibited veratridine-stimulated Na(+) influx in rat cortical synaptosomes with an IC(50) value of 28. 3 microM. Carteolol, levobunolol, timolol and atenolol were significantly less effective than betaxolol at reducing veratridine-evoked Na(+) influx. The ability of betaxolol to interact with neurotoxin site 2 of the Na(+) channel and inhibit Na(+) influx may have a role in its neuroprotective action in paradigms of excitotoxicity/ischaemia and in its therapeutic effect in glaucoma.

Topically applied betaxolol attenuates NMDA-induced toxicity to ganglion cells and the effects of ischaemia to the retina

The present results show that topically applied Betoptic(R)(0.5% betaxolol) to the rabbit or rat eye reaches the retina and can counteract the detrimental effects caused by ischaemia/reperfusion or N -methyl- d -aspartate (NMDA)-induced insults to the retina. Betaxolol is a beta(1)-adrenergic blocker but its neuroprotective action is generally thought to be due to its calcium channel blocking properties. Support for this view comes from studies on cultures of cortical neurones where it was found that betaxolol attenuated the NMDA-induced influx of(45)Ca(2+)while beta-adrenoreceptor agonists were ineffective. Topically applied Betoptic(R)to the rabbit eye was observed to reach the retina in maximal amounts within 60 min. Some of the substance was also found in the contralateral retina of the untreated eye suggesting that the agent reaches the retina by local systemic and retinal circulation. Concurrent treatment with Latanoprost(R)did not result in a greater amount of betaxolol reaching the retina. An ophthalmodynamometric procedure, which raises the intraocular pressure, was used to apply an ischaemic insult to the rabbit retina. After three days of reperfusion the b-wave of the electroretinogram was reduced by an average of 59% and the choline acetyltransferase immunoreactivity in the retina was almost obliterated. However, when experiments were carried out on animals which had been treated with one drop of Betoptic(R) twice daily for 4 weeks before ischaemia and also during the reperfusion phase, the reductions in both the b-wave of the electroretinogram and retinal choline acetyltransferase immunoreactivity due to ischaemia/reperfusion were greatly attenuated. Intravitreal injection of NMDA into the rat eye caused a decrease in the immunostaining for Thy-1 antigen which is associated with ganglion cells. The Thy-1 mRNA level was also reduced as was the mRNA for the common subunit of the NMDA receptor, the NR1 subunit. However, in animals subjected to a topical Betoptic(R)regime, before and after intravitreal injection of NMDA, the decreases in the mRNA levels of Thy-1 and NR1 were significantly attenuated.

Ocular medications in children

Many ocular medications are used by pediatricians or ophthalmologists caring for pediatric patients. Topical antibiotics are commonly prescribed for bacterial conjunctivitis, nasolacrimal duct obstructions, and ophthalmia neonatorum. Many new antiallergy eye drops are now available for the treatment of seasonal (hay fever) conjunctivitis. Dilating eye drops and antiglaucoma medications are generally used or prescribed by ophthalmologists, but pediatricians must be aware of their potentially serious systemic side effects. Before initiating treatment, physicians should evaluate the risks and benefits of ophthalmic medications, establish minimum dosages necessary to achieve a therapeutic benefit, and monitor children for local and systemic side effects.

Comparison of the ocular beta-blockers

OBJECTIVE

To compare the similarities and differences among the ocular beta-blockers. Important considerations when comparing these agents are the differences in systemic adverse effects, local tolerability, and cost.

DATA SOURCE

Information was retrieved from a MEDLINE search of the English-language literature and bibliographic reviews of review articles. Index terms included beta-blockers, glaucoma, timolol, levobunolol, betaxolol, metipranolol, and carteolol.

STUDY SELECTION

Emphasis was placed on eyedrop studies, as well as properly designed and executed clinical trials that assessed dosage, dosing interval, therapeutic response, adverse effects, and cost.

DATA EXTRACTION

Data from several studies were evaluated according to the study design, therapeutic response, and adverse effects.

DATA SYNTHESIS

Timolol maleate, levobunolol, metipranolol, and carteolol have similar effectiveness in lowering intraocular pressure; however, levobunolol and timolol gel forming solution may have an advantage of once-daily dosing. Studies have not been published comparing the clinical efficacy of timolol hemihydrate with that of other ocular beta-blockers. Metipranolol is cost effective in treating primary open-angle glaucoma; however, it has been associated with more ocular burning, stinging, and granulomatous anterior uveitis than other agents. The intrinsic sympathomimetic activity of carteolol has not yet displayed a definite advantage over the other agents in terms of optic disk perfusion and systemic adverse effects. The control of intraocular pressure with betaxolol has not always been as good as with timolol; however, betaxolol has some advantages over timolol and the other topical beta-blockers in terms of systemic adverse effects.

CONCLUSIONS

Considering cost, efficacy, and safety, timolol maleate is the recommended formulary agent because the other agents cannot consistently show an outstanding advantage.

Topical ophthalmic beta-adrenergic blockade for the treatment of glaucoma and ocular hypertension

Since the late 1970s, topical beta-adrenergic blockers have been the drugs of choice in treating ocular hypertension and associated glaucoma. The currently available drugs are timolol, betaxolol, levobunolol, metipranolol, and carteolol. All reduce intraocular pressure by decreasing the production of aqueous humor. Although these drugs are applied locally in the eye, they may enter the general circulation and reach concentrations high enough to cause systemic effects, including alterations in heart rate and rhythm, bronchoconstriction, dyslipidemia, and central nervous system abnormalities. Interactions with other drugs may also occur. Ocular beta- blockers differ in beta 1-selectivity (betaxolol is beta 1-selective, whereas the other drugs are nonselective) and in intrinsic sympathomimetic activity (ISA) or partial agonist properties (only carteolol possesses ISA). These differences give betaxolol and carteolol potential advantages in minimizing certain side effects. The advantage of betaxolol vis-à-vis systemic side effects is more clearly established than that of carteolol. Further systematic study is needed to determine what advantages, if any, are conferred by the presence of ISA.

Beta 1- and beta 2-antagonist activity of topically applied betaxolol and timolol in the systemic circulation

The beta 1- and beta 2-antagonist activity of betaxolol and timolol in the systemic circulation was studied ex-vivo after their ocular administration in thirty patients during cataract surgery. The patients received 40 microliters of 0.5% betaxolol or 0.25% timolol into the lower cul-de-sacs of both eyes. Blood samples were collected up to four h after instillation of the doses. Plasma concentrations of betaxolol and timolol were analyzed using a radioreceptor assay. The ex-vivo-beta 1-and beta 2-receptor occupancies corresponding drug plasma levels were calculated using radioligand binding techniques. The extent of beta 1-receptor occupancy of betaxolol in the systemic circulation was less than 20% and its beta 2-receptor occupancy was negligible. The extent of beta 1-receptor occupancy of timolol was about 65% and its beta 2-receptor occupancy about 80%. Because receptor occupancy is the basis of antagonist activity of beta-blocking agents, this study shows that the beta 1-antagonist activity of betaxolol in the systemic circulation is much less than that of timolol, and that its beta 2-antagonist activity is negligible. The study suggests that the reported side effects of betaxolol in patients with obstructive pulmonary diseases are not mediated via its beta 2-receptor blocking properties.

Assessment of bronchial effects following topical administration of butylamino-phenoxy-propanol-acetate, an oculoselective beta-adrenoceptor blocker in asthmatic subjects

1. Butylamino-phenoxy-propanol-acetate (BPPA) is a new topical oculoselective beta-adrenoceptor blocker for the reduction of intraocular pressure (IOP) in man. Its potency on the airways of normal subjects was identical with that of placebo. A study was carried out to determine the potential of BPPA to cause bronchoconstriction in mild asthmatics (FEV1 greater than or equal to 60% predicted) with normal IOP. 2. Twelve nonsmoking outpatients who bronchoconstricted to 0.25 or 0.50% of timolol eye drops (fall in FEV1 23.33 +/- 1.20% (mean +/- s.e. mean), range 16-30) were investigated in this double-masked, randomized, 3-period, crossover study. On three different occasions six incremental concentrations of BPPA (range: 0.1-2%; maximum cumulative concentration 4%), timolol (0.1-1%; 2%), and placebo were administered bilaterally until bronchoconstriction (decrease in FEV1 greater than or equal to 20% and in specific airway conductance (sGaw) greater than or equal to 35% simultaneously) or the maximum cumulative concentration was reached. 3. Airway response was measured as change in FEV1 and sGaw and dose-response curves to timolol, BPPA and placebo were performed. IOP was measured 3 h after the highest concentration of each study day. 4. Timolol caused dose-dependent falls in FEV1 and sGaw as well as clinical symptoms of respiratory distress in all subjects. The median cumulative concentrations of timolol required to decrease FEV1 by 20% and sGaw by 35% were 0.98% and 1.53%. Neither placebo (P greater than 0.05) nor BPPA (P greater than 0.05) caused a significant change in sGaw. A fall in FEV1 by 20% not accompanied by a simultaneous fall in sGaw by 35% was found in four subjects following BPPA and in five subjects following placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-induced pulmonary disease

OBJECTIVE

To review some of the types of drug-induced pulmonary disease reported in Australia.

DATA SOURCES

Reports of pulmonary side effects made to the Australian Adverse Drug Reaction Advisory Committee between December 1972 and March 1991. Reports of drug-induced pulmonary disease from other countries are also reviewed.

STUDY SELECTION

Only reports involving large patient numbers are included in the review to limit the bias likely from limited patient numbers.

DATA EXTRACTION

The incidence of adverse responses to a range of commonly used drugs from other countries is compared with reports to the Australian Adverse Drug Reaction Advisory Committee in the last 19 years.

DATA SYNTHESIS

Of adverse drug reactions reported in Australia in the last 19 years 7.7% were of a pulmonary side effect and 55% of these involved a syndrome of airway dysfunction. Bronchospasm and cough were the two most common symptoms of airway dysfunction and beta-blocking drugs and radio contrast media were the drug groups most commonly reported to cause them. These figures are similar to data reported from other countries. Some of the more commonly occurring types of drug-induced disease affecting either the airways or the lung interstices are reviewed.

CONCLUSIONS

Medical practitioners should maintain a high index of clinical suspicion that any unexplained pulmonary disease could be caused by a drug. Most of these reactions are reversible if the drug is withdrawn in time and if additional appropriate measures are taken as required.

Ocular carteolol. A review of its pharmacological properties, and therapeutic use in glaucoma and ocular hypertension

Carteolol is a relatively potent nonselective beta-adrenoceptor antagonist with partial agonist activity. It is used topically to reduce elevated intraocular pressure (IOP) in patients with glaucoma or ocular hypertension. Twice-daily ocular administration of carteolol 1 or 2% lowers IOP by approximately 32% on average in patients with these conditions, an efficacy equivalent to that of timolol 0.25 or 0.5%. Carteolol eyedrops lack local anaesthetic activity, appear to cause less local irritation than timolol, and produce less pronounced decreases in heart rate or dyspnoea, possibly due to partial agonist activity. The latter activity may also improve retinal perfusion. Thus, although additional comparative trials are needed to accurately assess the precise place of carteolol in therapy, this drug offers a useful alternative to timolol in the management of conditions associated with a raised IOP, and may have advantages in older patients with regard to its tolerability profile, although careful monitoring is still wise.