Controlled ocular timolol delivery: systemic absorption and intraocular pressure effects in humans

Short-term Efficacy and Safety of Topical β-Blockers (Timolol Maleate Ophthalmic Solution, 0.5%) in Acute Migraine: A Randomized Crossover Trial

Importance

Oral β-blockers used for the prevention of migraine headache are not effective for the treatment of acute pain. Small case series have suggested that topically applied β-blockers may be useful in the management of acute migraine pain, warranting evaluation with randomized clinical trials.

Objective

To evaluate the short-term efficacy and safety of topically applied timolol maleate ophthalmic solution, 0.5%, compared with topically applied placebo eyedrops in the treatment of acute migraine attacks.

Design, Setting, and Participants

In this randomized, masked placebo-controlled crossover trial conducted from May 27, 2015, to August 28, 2017, 50 patients with migraine were randomized to receive either timolol eyedrops, 0.5%, or a placebo eyedrop (carboxymethyl cellulose, 0.5%). After a 3-month treatment period, patients completed a 1-month washout period and were crossed over to receive the opposite treatment for a final 3 months. Analysis was performed on a modified intent-to-treat basis.

Intervention

After random assignment, patients were instructed to use 1 drop of the assigned medication in each eye at the earliest onset of migraine.

Main Outcomes and Measures

The main outcome measure was reduction in pain score with treatment. The primary end point was reduction of pain score by 4 points, or to zero, 20 minutes after instillation of the eyedrop.

Results

Of the 50 patients, 42 (84%) were females and the mean (SD) age was 27.3 (11.3) years. Of a total of 619 migraine attacks, 284 (46%) were treated with timolol, 271 (44%) were treated with the placebo, and 64 (10%) occurred during the washout period when no study medications were used. Seven patients (14%) withdrew after randomization. A total of 233 of the timolol-treated migraine attacks (82%) were associated with a reduction in pain score by 4 points, or to zero, at 20 minutes compared with 38 of the placebo-treated attacks (14%), with a difference of 68 percentage points (95% CI, 62-74 percentage points). A generalized estimating equation analysis revealed that pain score reduction at 20 minutes was greater in the timolol group compared with the placebo group by a mean (SE) of 4.63 points (0.34) (P < .001).

Conclusions and Relevance

This randomized crossover trial supports consideration of timolol eyedrops in the acute treatment of migraine. Further research is warranted to determine if the improvements observed are sustained for a longer follow-up and with larger groups.

Trial Registration

CTRI/2015/05/005829, UTN: U1111-1167-6439.

Biosafety, Functionalities, and Applications of Biomedical Micro/nanomotors

Due to their unique ability to actively move, micro/nanomotors offer the possibility of breaking through the limitations of traditional passive drug delivery systems for the treatment of many diseases, and have attracted the increasing attention of researchers. However, at present, the realization of many advantages of micro/nanomotors in disease treatment in vivo is still in its infancy, because of the complexity and particularity of diseases in different parts of human body. In this Minireview, we first focus on the biosafety and functionality of micro/nanomotors as a biomedical treatment system. Then, we address the treatment difficulties of various diseases in vivo (such as ophthalmic disease, orthopedic disease, gastrointestinal disease, cardiovascular disease, and cancer), and then review the research progress of biomedical micro/nanomotors in the past 20 years, Finally, we propose the challenges in this field and possible future development directions.

Challenges and strategies for the delivery of biologics to the cornea

Biologics, like peptides, proteins and nucleic acids, have proven to be promising drugs for the treatment of numerous diseases. However, besides the off label use of the monoclonal antibody bevacizumab for the treatment of corneal neovascularization, to date no other biologics for corneal diseases have reached the market. Indeed, delivering biologics in the eye remains a challenge, especially at the level of the cornea. While it appears to be a rather accessible tissue for the administration of drugs, the cornea in fact presents several anatomical barriers to delivery. In addition, also intracellular delivery barriers need to be overcome to achieve a promising therapeutic outcome with biologics. This review outlines efforts that have been reported to successfully deliver biologics into the cornea. Biochemical and physical methods for achieving delivery of biologics in the cornea are discussed, with a critical view on their efficacy in overcoming corneal barriers.

A Case of Recurrent Painful Ophthalmoplegic Neuropathy Successfully Treated with Beta-blocker Eye Drop Instillation

Recurrent painful ophthalmoplegic neuropathy (RPON) is a rare disorder, which typically occurs in children, and causes headaches and unilateral oculomotor palsy. Early high-dose corticosteroid therapy is recommended to rapidly resolve acute episodes. However, the pathophysiology and therapeutic options for this disorder remain to be fully elucidated. We report a case with typical clinical features of RPON successfully treated with beta-blocker eye drop instillation after the effects of high-dose corticosteroid and other therapies were not sufficient. We propose that beta-blocker eye drop instillation should be considered for patients with corticosteroid-resistant RPON.

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.

Overcoming the Anatomical and Physiological Barriers in Topical Eye Surface Medication Using a Peptide-Decorated Polymeric Micelle

The sealed anatomical features of the eye and its physiological activity that rapidly removes drugs are called anatomical and physiological barriers, which are the cause of more than 90% of drug loss. This aspect remains a critical issue in eye surface medication. Thus, promoting tissue permeability of drugs as well as prolonging their retention on the eye surface can improve their bioavailability and enhance their therapeutic effects. Thanks to the existence of a negatively charged mucin layer on the eye surface, several peptide-decorated polymeric micelles were prepared to enhance the interaction between the micelle and eye surface, thus prolonging the drug retention on the eye surface and promoting its tissue permeability. Tacrolimus (also known as FK506) is a hydrophobic macrolide immunosuppressant used to treat dry eye syndrome and other eye diseases. However, its hydrophobic nature makes its delivery as a topical eye surface medication difficult, with the risk of side effects due to overdoses. Therefore, the aim of this work is to evaluate the ability of FK506 micelles in promoting their permeability on the eye surface. Our results showed that the positively charged nanomicelles could significantly prolong FK506 retention on the eye surface and enhance its corneal permeability in ex vivo and in vivo conditions. FK506 nanomicelles exhibited superior curing effects against dry eye diseases than the FK506 suspension and a commercial FK506 formula. It exerted better inhibitory effects on eye surface inflammation and corneal epithelium apoptosis when examined by a slip lamp and a transferase-mediated dUTP nick end labeling assay, respectively. Further assays revealed the higher suppressive effects on the expression of several inflammation-related factors at an mRNA and protein level. Hence, our results suggested that these positively charged nanomicelles might be a good drug delivery system for ocular surface medication.

Corneal and conjunctival drug permeability: Systematic comparison and pharmacokinetic impact in the eye

On the surface of the eye, both the cornea and conjunctiva are restricting ocular absorption of topically applied drugs, but barrier contributions of these two membranes have not been systemically compared. Herein, we studied permeability of 32 small molecular drug compounds across an isolated porcine cornea and built a quantitative structure-property relationship (QSPR) model for the permeability. Corneal drug permeability (data obtained for 25 drug molecules) showed a 52-fold range in permeability (0.09-4.70 × 10^-6 cm/s) and the most important molecular descriptors in predicting the permeability were hydrogen bond donor, polar surface area and halogen ratio. Corneal permeability values were compared to their conjunctival drug permeability values. Ocular drug bioavailability and systemic absorption via conjunctiva were predicted for this drug set with pharmacokinetic calculations. Drug bioavailability in the aqueous humour was simulated to be <5% and trans-conjunctival systemic absorption was 34-79% of the dose. Loss of drug across the conjunctiva to the blood circulation restricts significantly ocular drug bioavailability and, therefore, ocular absorption does not increase proportionally with the increasing corneal drug permeability.

Glaucoma: Biological Trabecular and Neuroretinal Pathology with Perspectives of Therapy Innovation and Preventive Diagnosis

Glaucoma is a common degenerative disease affecting retinal ganglion cells (RGC) and optic nerve axons, with progressive and chronic course. It is one of the most important reasons of social blindness in industrialized countries. Glaucoma can lead to the development of irreversible visual field loss, if not treated. Diagnosis may be difficult due to lack of symptoms in early stages of disease. In many cases, when patients arrive at clinical evaluation, a severe neuronal damage may have already occurred. In recent years, newer perspective in glaucoma treatment have emerged. The current research is focusing on finding newer drugs and associations or better delivery systems in order to improve the pharmacological treatment and patient compliance. Moreover, the application of various stem cell types with restorative and neuroprotective intent may be found appealing (intravitreal autologous cellular therapy). Advances are made also in terms of parasurgical treatment, characterized by various laser types and techniques. Moreover, recent research has led to the development of central and peripheral retinal rehabilitation (featuring residing cells reactivation and replacement of defective elements), as well as innovations in diagnosis through more specific and refined methods and inexpensive tests.

Impact of Chemical Structure on Conjunctival Drug Permeability: Adopting Porcine Conjunctiva and Cassette Dosing for Construction of In Silico Model

Conjunctiva occupies most of the ocular surface area, and conjunctival permeability affects ocular and systemic drug absorption of topical ocular medications. Therefore, the aim of this study was to obtain a computational in silico model for structure-based prediction of conjunctival drug permeability. This was done by employing cassette dosing and quantitative structure-property relationship (QSPR) approach. Permeability studies were performed ex vivo across fresh porcine conjunctiva and simultaneous dosing of a cassette mixture composed of 32 clinically relevant drug molecules with wide chemical space. The apparent permeability values were obtained using drug concentrations that were quantified with liquid chromatography tandem-mass spectrometry. The experimental data were utilized for building a QSPR model for conjunctival permeability predictions. The conjunctival permeability values presented a 17-fold range (0.63-10.74 × 10^-6 cm/s). The final QSPR had a Q² value of 0.62 and predicted the external test set with a mean fold error of 1.34. The polar surface area, hydrogen bond donor, and halogen ratio were the most relevant descriptors for defining conjunctival permeability. This work presents for the first time a predictive QSPR model of conjunctival drug permeability and a comprehensive description on conjunctival isolation from the porcine eye. The model can be used for developing new ocular drugs.

Topical medication instillation techniques for glaucoma

BACKGROUND

Glaucoma is a leading cause of irreversible blindness worldwide and the second most common cause of blindness after cataracts. The primary treatment for glaucoma aims to lower intraocular pressure (IOP) with the use of topical medicines. Topical medication instillation techniques, such as eyelid closure and nasolacrimal occlusion when instilling drops, have been proposed as potential methods to increase ocular absorption and decrease systemic absorption of the drops.

OBJECTIVES

To investigate the effectiveness of topical medication instillation techniques compared with usual care or another method of instillation of topical medication in the management of glaucoma or ocular hypertension.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2016, Issue 12), MEDLINE Ovid (1946 to 8 December 2016), Embase Ovid (1947 to 8 December 2016), PubMed (1948 to 8 December 2016), LILACS (Latin American and Caribbean Health Sciences Literature Database) (1982 to 8 December 2016), International Pharmaceutical Abstracts Database (1970 to 8 December 2016), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com) (last searched 13 May 2013), ClinicalTrials.gov (www.clinicaltrials.gov) (searched 8 December 2016) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en) (searched 8 December 2016). We did not use any date or language restrictions in the electronic searches for trials.

SELECTION CRITERIA

We included randomized controlled trials which had compared any topical medication instillation technique with usual care or a different method of instillation of topical medication.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened records from the searches for eligibility, assessed the risk of bias, and extracted data. We followed methods recommended by Cochrane.

MAIN RESULTS

We identified two trials (122 eyes of 61 participants) that had evaluated a topical medication instillation technique. We also identified two ongoing trials. Both included trials used a within-person design and administered prostaglandin monotherapy for glaucoma or ocular hypertension. Because the trials evaluated different instillation techniques and assessed different outcomes, we performed no meta-analysis.One trial, conducted in the US, evaluated the effect of eyelid closure (one and three minutes) versus no eyelid closure on lowering IOP. At one to two weeks' follow-up, reduction in IOP was similar in the eyelid closure group and the no eyelid closure group (mean difference (MD) -0.33 mmHg, 95% confidence interval (CI) -0.8 to 1.5; 51 participants; moderate-certainty evidence).The second trial, conducted in Italy, evaluated the effect of using an absorbent cloth to wipe excess fluid after instillation (fluid removal) versus not using an absorbent cloth (no removal) on reducing dermatologic adverse events. At four months' follow-up, eyelashes were shorter among eyes in the fluid removal group compared with the no fluid removal group (MD -1.70 mm, 95% CI -3.46 to 0.06; 10 participants; low-certainty evidence). Fewer eyes showed skin hyperpigmentation in the eyelid region towards the nose in the fluid removal group compared with the no removal group (RR 0.07, 95% CI 0.01 to 0.84; 10 participants; low-certainty evidence); however, the difference was uncertain in the eyelid region towards the temples (RR 0.44, 95% CI 0.07 to 2.66; 10 participants; low-certainty evidence). The effect hypertrichosis (excessive hair growth) was uncertain between groups (RR 1.00, 95% CI 0.17 to 5.98; 10 participants; low-certainty evidence).Neither trial reported other outcomes specified for this review, including the proportion of participants with IOP less than 21 mmHg; participant-reported outcomes related to the ease, convenience, and comfort of instillation techniques; physiologic measurements of systemic absorption; escalation of therapy; mean change in visual fields; optic nerve progression; mean change in best-corrected visual acuity; proportion in whom glaucoma developed; quality of life outcomes; or cost-effectiveness outcomes. Neither trial reported data at follow-up times of more than four months.

AUTHORS' CONCLUSIONS

Evidence to evaluate the effectiveness of topical medication instillation techniques for treatment of glaucoma is lacking. It is unclear what, if any, effects instillation techniques have on topical medical therapy for glaucoma.

Pharmacotherapy and Adherence Issues in Treating Elderly Patients with Glaucoma

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

Tower microneedle via reverse drawing lithography for innocuous intravitreal drug delivery

The "tower microneedle" (TM) via reverse drawing lithography for intravitreal injection by fabricating a long hollow microneedle on the blunt hypodermic needle: The hollow hole between the microneedle and hypodermic needle is aligned concentrically, and fifteen degree bevel angle is introduced to TM by laser cutting to achieve intravitreal injection with minimal damage to eye tissue.

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.

A review of implantable intravitreal drug delivery technologies for the treatment of posterior segment eye diseases

Intravitreal implantable device technology utilizes engineered materials or devices that could revolutionize the treatment of posterior segment eye diseases by affording localized drug delivery, responding to and interacting with target sites to induce physiological responses while minimizing side-effects. Conventional ophthalmic drug delivery systems such as topical eye-drops, systemic drug administration or direct intravitreal injections do not provide adequate therapeutic drug concentrations that are essential for efficient recovery in posterior segment eye disease, due to limitations posed by the restrictive blood-ocular barriers. This review focuses on various aspects of intravitreal drug delivery such as the impediment of the blood-ocular barriers, the potential sites or intraocular drug delivery device implantation, the various approaches employed for ophthalmic drug delivery and includes a concise critical incursion into specialized intravitreal implantable technologies for the treatment of anterior and posterior segment eye disease. In addition, pertinent future challenges and opportunities in the development of intravitreal implantable devices is discussed and explores their application in clinical ophthalmic science to develop innovative therapeutic modalities for the treatment of various posterior segment eye diseases. The inherent structural and functional properties, the potential for providing rate-modulated drug delivery to the posterior segment of the eye and specific development issues relating to various intravitreal implantable drug delivery devices are also expressed in this review.

Challenges and obstacles of ocular pharmacokinetics and drug delivery

Modern biological research has produced increasing number of promising therapeutic possibilities for medical treatment. These include for example growth factors, monoclonal antibodies, gene knockdown methods, gene therapy, surgical transplantations and tissue engineering. Ocular application of these possibilities involves drug delivery in many forms. Ocular drug delivery is hampered by the barriers protecting the eye. This review presents an overview of the essential factors in ocular pharmacokinetics and selected pharmacological future challenges in ophthalmology.

Local delivery of antineoplastic agents by controlled-release polymers for the treatment of malignant brain tumours

Recent advances in the treatment of malignant brain tumours have focused on the development of targeted local delivery of therapeutic agents, which combine various antineoplastic strategies that include cytotoxic, anti-angiogenic and immunomodulatory mechanisms, among others. The introduction of local delivery devices for sustained administration of antineoplastic agents represents a new opportunity to effectively treat these malignancies by facilitating the intracranial administration of safe and clinically efficacious doses for prolonged periods of time in a controlled fashion. This technology circumvents the need for high systemic doses with potentially harmful toxicities, bypasses the blood-brain barrier and can be tailored to deliver new agents with complex pharmacological properties. Based on local delivery strategies, new delivery systems, including convection-enhanced delivery and microchips, have been developed. As a result, recent advances in tumour biology have been adopted as potentially translatable treatments and are undergoing preclinical and clinical evaluation at present. These novel approaches could improve the prognosis of patients with these tumours.

Systemic adverse effects of topical ocular treatments

Some eyedrops, gels or ointments may cause adverse effects as serious as those observed with systemic therapies. Because of their relatively poor penetration into eye tissue, ophthalmic drugs usually contain high concentrations of their active ingredient. Asking patients about these drugs to prevent interactions is useful when prescribing a new systemic treatment. Conversely, it is advisable to ask about ophthalmic drugs during the etiological investigation of possible iatrogenic effects.

Cardiovascular effects of timolol maleate, brimonidine or brimonidine/timolol maleate in concomitant therapy

PURPOSE

To examine the influence on maximal exercise performance in young healthy volunteers of timolol 0.5%, brimonidine 0.2% or placebo versus brimonidine 0.2% and timolol 0.5% used concomitantly.

METHODS

The subjects in this prospective, double-masked, crossover comparison were dosed 15 min prior to treadmill testing. A period of 1 week was allowed between tests.

RESULTS

The 20 subjects who completed the trials (average age 24.5 +/- 7.4) had a mean maximum exercise heart rate of 196 +/- 12 bpm for placebo, 182 +/- 13 bpm for timolol, 187 +/- 10 bpm for brimonidine, and 186 +/- 11 bpm for timolol/brimonidine concomitant therapy (p < 0.005). During recovery, the placebo group demonstrated a statistically higher systolic blood pressure (min 6) and pulse (mins 2 and 4) (p < 0.01). In addition, subjects treated with timolol/brimonidine demonstrated more premature contractions (atrial or ventricular) overall during exercise and recovery (p = 0.01). The brimonidine and concomitant treatment groups showed the greatest number of adverse events per subject, the most common of which were dizziness and fatigue (p = 0.031).

CONCLUSION

This study suggests that both timolol and brimonidine, used alone and concomitantly, cause cardiovascular effects consistent with their pharmacology.

Ocular preparations: the formulation approach

The main aim of pharmacotherapeutics is the attainment of an effective drug concentration at the intended site of action for a sufficient period of time to elicit the response. A major problem being faced in ocular therapeutics is the attainment of an optimal concentration at the site of action. Poor bioavailability of drugs from ocular dosage forms is mainly due to the tear production, non-productive absorption, transient residence time, and impermeability of corneal epithelium. This article reviews: (1) the barriers that decrease the bioavailability of an ophthalmic drug; (2) the objectives to be considered in producing optimal formulations; and (3) the approaches being used to improve the corneal penetration of a drug molecule and delay its elimination from the eye. The focus of this review is on the recent developments in topical ocular drug delivery systems, the rationale for their use, their drug release mechanism, and the characteristic advantages and limitations of each system. In addition, the review attempts to give various analytical procedures including the animal models and other models required for bioavailability and pharmacokinetic studies. The latter can aid in the design and predictive evaluation of newer delivery systems. The dosage forms are divided into the ones which affect the precorneal parameters, and those that provide a controlled and continuous delivery to the pre- and intraocular tissues. The systems discussed include: (a) the commonly used dosage forms such as gels, viscosity imparting agents, ointments, and aqueous suspensions; (b) the newer concept of penetration enhancers, phase transition systems, use of cyclodextrins to increase solubility of various drugs, vesicular systems, and chemical delivery systems such as the prodrugs; (c) the developed and under-development controlled/continuous drug delivery systems including ocular inserts, collagen shields, ocular films, disposable contact lenses, and other new ophthalmic drug delivery systems; and (d) the newer trends directed towards a combination of drug delivery technologies for improving the therapeutic response of a non-efficacious drug. The fruitful resolution of the above-mentioned technological suggestions can result in a superior dosage form for both topical and intraocular ophthalmic application.

Effect of timolol 0.5% gel and solution on pulmonary function in older glaucoma patients

PURPOSE

To evaluate the effect of timolol maleate solution or gel forming solution versus placebo on pulmonary function in patients with primary open-angle glaucoma or ocular hypertension without reactive airway disease.

METHODS

After a screening visit, each patient was randomized by a Latin square technique to receive placebo twice daily, 0.5% timolol solution twice daily, or 0.5% timolol gel once a day (placebo given as second dose) to each eye for 2 weeks. Subjects then were crossed over to the two other treatments for 2-week treatment intervals. At each visit, patients were received a dose 15 minutes before pulmonary function testing.

RESULTS

This study began with 25 patients, and 20 finished the trial. There was no difference between treatment groups for the forced expiratory volume at one second (FEV1), forced vital capacity (FVC), FEV1/FVC ratio (P > 0.1). The mean FEV1 for timolol solution, timolol gel, and placebo was 2.42 L, 2.45 L, and 2.50 L, respectively. The mean FVC for timolol solution, timolol gel, and placebo was 3.33 L, 3.38 L, and 3.44 L, respectively. No difference in intraocular pressure was observed between the timolol solution (17.1 +/- 3.3 mm Hg) and timolol gel (17.1 +/- 3.6 mm Hg) between the treatment periods (P > 0.1). No difference in side effects was observed between treatment groups (P > 0.05).

CONCLUSIONS

In older patients with primary open-angle glaucoma or ocular hypertension without reactive airway disease, nonselective beta-blockers should not worsen pulmonary function.

Pharmacokinetics of topical beta-adrenergic antagonists in rabbit aqueous humor evaluated with the microdialysis method

The microdialysis method was used to evaluate the pharmacokinetics of the beta-adrenergic antagonists carteolol and timolol and the new ophthalmic solution WP-934 in rabbit aqueous humor, following instillation. A probe with a microdialysis membrane (length, 5 mm; diameter, 0.2 mm) was implanted in the anterior chamber of the pigmented rabbit and perfused with Ringer's solution. Twenty microliters of 0.5% timolol maleate (0.5% Timoptol(R)), 2% carteolol hydrochloride (2% Mikelan(R)), or a novel preparation of 0.5% timolol maleate (WP-934) that gels after instillation were then instilled. The concentrations of these drugs in dialysates were measured using high-performance liquid chromatography and an electrochemical detection system. In vitro relative recovery of the membrane with timolol and carteolol was approximately 17.5% and 21. 6%, respectively. Timolol and carteolol levels in aqueous humor increased rapidly after instillation of Timoptol and Mikelan and reached maximal levels (Cmax) within 60 minutes. The Cmax of carteolol (4.25 microg ml-1) was lower than that of timolol (5.52 microg ml-1), suggesting that the corneal permeability of timolol is higher than that of carteolol. After instillation of WP-934, the Cmax of timolol (12.32 microg ml-1) was 2.2-fold higher than that after instillation of Timoptol. However, t1/2 values of beta-adrenergic antagonists after instillation of the three preparations were not significantly different. These data suggest that the microdialysis technique is useful for continuous monitoring of aqueous levels of beta-blockers and for analysis of their pharmacokinetic parameters while requiring much fewer animals than conventional sampling with paracentesis.

Preparation of silicone microspheres by emulsion polymerization: application to the encapsulation of a hydrophilic drug

The objective of this work was to evaluate the ability of appropriate silicone elastomers to encapsulate hydrophilic compounds in microspheres prepared according to a multiphase emulsion-polymerization process. The particle size of the microspheres can be modified by controlling the usual emulsification parameters, such as the viscosity of the different phases, shear rates and surface activity properties of additives. The encapsulation efficiencies of a hydrophilic drug, propranolol hydrochloride, were very high but its release rates were very slow. Osmotic agents such as glycerol and propylene glycol did not enhance the release rate, whereas it was slightly increased by both sodium chloride addition and higher drug loading.

Ophthalmic drug delivery systems--recent advances

Eye-drops are the conventional dosage forms that account for 90% of currently accessible ophthalmic formulations. Despite the excellent acceptance by patients, one of the major problems encountered is rapid precorneal drug loss. To improve ocular drug bioavailability, there is a significant effort directed towards new drug delivery systems for ophthalmic administration. This chapter will focus on three representative areas of ophthalmic drug delivery systems: polymeric gels, colloidal systems, cyclodextrins and collagen shields. Hydrogels generally offer a moderate improvement of ocular drug bioavailability with the disadvantage of blurring of vision. In situ activated gel-forming systems are preferred as they can be delivered in drop form with sustained release properties. Colloidal systems including liposomes and nanoparticles have the convenience of a drop, which is able to maintain drug activity at its site of action and is suitable for poorly water-soluble drugs. Among the new therapeutic approaches in ophthalmology, cyclodextrins represent an alternative approach to increase the solubility of the drug in solution and to increase corneal permeability. Finally, collagen shields have been developed as a new continuous-delivery system for drugs that provide high and sustained levels of drugs to the cornea, despite a problem of tolerance. It seems that new tendency of research in ophthalmic drug delivery systems is directed towards a combination of several drug delivery technologies. There is a tendency to develop systems which not only prolong the contact time of the vehicle at the ocular surface, but which at the same time slow down the elimination of the drug. Combination of drug delivery systems could open a new directive for improving results and the therapeutic response of non-efficacious systems.

Ocular mini-tablets for controlled release of timolol: evaluation in rabbits

Topical delivery of timolol by inserts or similar controlled-release devices may offer distinct advantages over administration by eyedrops. The purpose of this investigation was the evaluation in rabbits of ophthalmic inserts (denominated mini-tablets, MT) for sustained/controlled release of timolol maleate (TiM). The MTs (diameter 3.5 mm, thickness 1.5 mm, average TiM content 0.34 or 0.68 mg) were prepared by compressing appropriate mixtures of powders with a standard tabletting machine. A thin, rate-controlling membrane was applied over the devices by spraying aqueous dispersions of acrylic copolymers. A first series of different (uncoated and coated) MTs were tested for release of TiM to the lacrimal fluid, using commercial eyedrops (Timoptol 0.5%) as a reference standard. Two MTs (one of which was coated) and the same reference solution were then selected for an ocular absorption study. Analysis of TiM in the aqueous humor indicated that the coated MT was capable of maintaining low and steady levels of TiM for at least 19 h, while the other device, identical but uncoated, produced a prolonged-pulse effect lasting about 8 h. The apparent mean residence time (MRT) of TiM in the aqueous humor was 1.3 h for the reference solution, 3.2 h for the uncoated MT, and 5.7 h for the coated one. The present preliminary results point to the potential validity of coated mini-tablets as simple systems for controlled ocular delivery of timolol.