A comparison of the efficacy and duration of action of topically applied proxymetacaine using a novel ophthalmic delivery system versus eye drops in healthy young volunteers

A review of topically administered mini-tablets for drug delivery to the anterior segment of the eye

OBJECTIVES

The human eye is a unique and intricate structure which has made drug delivery to the eye a formidable undertaking. Anterior-segment eye diseases are ubiquitous, especially among elderly patients, and conventional eye drops, although a first-choice dosage form, are not always an efficient treatment option. The development of novel drug delivery systems for improved treatment is therefore imperative.

KEY FINDINGS

In an attempt to circumvent the obstacles presented by the structure of the eye, advanced systems such as ocular mini-tablets have been developed. In this review, a concerted effort has been made to provide a detailed overview of topically administered ocular mini-tablets and other solid devices for drug delivery to the anterior segment of the eye. These mini-tablets have been shown in vitro and in vivo to have significant advantages in comparison with liquid preparations. This is a step toward attaining better patient convenience and compliance, which are critical factors.

SUMMARY

Solid ophthalmic dosage forms have several advantages that can contribute to assisting with patient compliance and, ultimately, effective disease treatment. In addition to the challenges associated with topical ocular drug delivery, the shortcomings of conventional eye drops, advantages of mini-tablets, and improvements to date to these systems are discussed. The requirement for further advancements in the ocular field is also emphasized.

Randomised controlled single-blind study of conventional versus depot mydriatic drug delivery prior to cataract surgery

BACKGROUND

A prerequisite for safe cataract surgery is an adequately dilated pupil. The authors conducted a trial to assess the efficacy (in terms of pupil diameter) of a depot method of pre-operative pupil dilatation, as compared with repeated instillations of drops (which is time-consuming for the nursing staff and uncomfortable for the patient).

METHODS

A prospective randomised masked trial was conducted comprising 130 patients with no significant ocular history undergoing elective clear corneal phacoemulsification. 65 patients had mydriatic drops (Tropicamide 1%, Phenylephrine 2.5%, Diclofenac sodium 0.1%) instilled prior to surgery, 65 had a wick soaked in the same drop mixture placed in the inferior fornix. Horizontal pupil diameters were recorded on a millimetre scale immediately prior to surgery.

RESULTS

There was no significant difference in pupil size between the two groups (p = 0.255, Student's t-test).

CONCLUSION

There was no significant difference between the mydriasis obtained with the depot system compared with conventional drop application. Use of a depot mydriatic delivery system appears to be a safe and efficient method of drug delivery.

TRIAL REGISTRATION

International Standard Randomised Controlled Trial Number Register ISRCTN78047760.

Efficacy and safety of three ophthalmic inserts for topical anaesthesia of the cornea. An exploratory comparative dose-ranging, double-blind, randomized trial in healthy volunteers

BACKGROUND

Cataract surgery requires prolonged anaesthesia, concomitant with permanent hydration and lubrication of the cornea, in order to provide a clear view of the operation area.

AIMS

The primary objective of the study was to assess several formulae of a soluble ophthalmic insert: TOPICSERT [bupivacaine (Bupi) + hyaluronic acid (HA) or sodium hyaluronate] in terms of complete and long-lasting anaesthesia of the cornea. The hydration properties of HA were not assessed in this study.

METHODS

In a prospective double-blind, cross-over, randomized study, with latin-square allocation of treatments, 16 healthy volunteers received a single dose of each formula (A, 1 mg Bupi and 0.1 mg HA; B, 0.5 mg Bupi and 0.1 mg HA; C, 1 mg Bupi and 0 mg HA, and D acting as a placebo) via the ocular route with 1 week of wash-out between each period. Corneal anaesthesia was measured using a Cochet-Bonnet esthesiometer.

RESULTS

There was a statistically significant difference between treatments with regard to the main criterion (complete anaesthesia lasting at least 20 min) when general association statistics were used (Mantel-Haenzel test, P < 0.0001): 68.75% (n = 11) of subjects receiving treatment A, 37.5% (n = 6) receiving treatment B, and 87.5% (n = 14) on treatment C reached complete and satisfactory anaesthesia, while this was not achieved in any of the subjects receiving placebo. Ninety-five percent confidence intervals of the difference between treatments were as follows: treatment A vs. B (-0.03, 0.66), treatment A vs. C (-0.47, 0.10), treatment B vs. C (-0.84, - 0.16). Only the difference between B and C was statistically significant (adjusted probability by the method of Bonferroni, P < 0.001). When complete anaesthesia was reached, mean (+/-SD) duration of anaesthesia was as follows: 20.7 (+/-6.5), 15.3 (+/-11.4) and 24.7 (+/-7.6) min for treatments A, B, C, respectively.

CONCLUSIONS

Bupivacaine 1 mg seems to be the efficient and safe dose. The value of hyaluronic acid as a corneal hydration agent and used in association with bupivacaine will be the subject of further studies.

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.

Insoluble ionic complexes of polyacrylic acid with a cationic drug for use as a mucoadhesive, ophthalmic drug delivery system

We have developed a new mucoadhesive drug delivery formulation based on an ionic complex of partially neutralized poly(acrylic acid) (PAA) and a highly potent beta blocker drug, levobetaxolol x hydrochloride (LB x HCl), for use in the treatment of glaucoma. PAA was neutralized with sodium hydroxide to varying degrees of neutralization. Aqueous solutions containing concentrations of LB x HCl equivalent to the degree of PAA neutralization were added to the PAA solutions and formed insoluble complexes, which were isolated. The complex formation was followed by turbidimetric titration, and the complexes were characterized by IR and 1H NMR spectroscopy. Complexes were prepared with varying degrees of drug loading, such that the same PAA chain would have free -COOH groups for mucoadhesion along with ionic complexes of LB x H+ with COO- groups. Thin films of the complexes dissociated to release the drug by ion exchange with synthetic tear fluid. The films shrunk continuously during release of the drug and dissolved completely in 1 h. Solid inserts of these films could be useful as a mucoadhesive ophthalmic drug delivery system.

Corneal sensation after topical anesthesia

PURPOSE

To compare the topical effects of tetracaine, lidocaine, and bupivacaine on corneal sensitivity in normal eyes.

METHODS

Corneal touch sensitivity was measured with a Cochet-Bonnet anesthesiometer before and at 2.5-minute intervals after instillation of the anesthetic agent, until baseline levels had been reestablished. Seventeen healthy volunteers were randomized into five groups. Group 1 included 0.5% tetracaine (n = 6); group 2, 4% lidocaine (n = 8); group 3, 0.75% bupivacaine (n = 8); group 4, 0.5% tetracaine + 4% lidocaine (n = 5); and group 5, 0.5% tetracaine + 0.75% bupivacaine (n = 7).

RESULTS

The duration of anesthesia showed no differences between groups 1, 3, and 5. Although there was no difference between groups 2 and 4, both groups demonstrated significantly longer effects than groups 1, 3, and 5 (p < 0.005).

CONCLUSION

The application of 4% lidocaine results in a significantly prolonged topical anesthetic effect when compared with tetracaine and bupivacaine.

The formulation of drug for ocular administration

The different barriers that slow the penetration of active ingredients administered by the ocular route are described, and some novel dosage forms designed for this route are discussed. Both precorneal and corneal factors considerably restrict ocular penetration. The low bioavailability of classical ophthalmic dosage forms can be improved by several approaches, particularly by increasing the time the active ingredients remain in contact with the eye tissues. The new dosage forms are reviewed according to their type and their drug release mechanisms. The characteristics, advantages, and limitations of each are outlined. The potential of these dosage forms can be expected to enhance development. They offer prolonged effectiveness, reproducibility, fewer unwanted side effects, and improved tolerance.

Touch sensitivity of the eyelid margin and palpebral conjunctiva

Using a slit-lamp biomicroscope mounted Cochet-Bonnet aesthesiometer, the touch sensitivity of the eyelid margin and palpebral conjunctiva was determined for both upper and lower lids in 30 subjects. Thresholds for the occlusal surface of the lid, the marginal angle and the middle of the tarsus were measured centrally. A significantly higher touch sensitivity was found for the marginal zone compared with the occlusal surface, and tarsal conjunctival sensitivity was substantially the lowest. The occlusal and marginal zones of the lower lid displayed a significantly higher touch sensitivity than the upper lid but the tarsal sensitivity of the two lids was similar. The sharp peaking of sensitivity at the leading edge of each eyelid provides a mechanism for the detection of superficial foreign bodies and presumably augments the protective role of the cornea. A large inter-subject variation in marginal touch sensitivity was found which may explain individual variation in contact lens adaptation.