Conjunctival tissue pharmacokinetic properties of topical azithromycin 1% and moxifloxacin 0.5% ophthalmic solutions: a single-dose, randomized, open-label, active-controlled trial in healthy adult volunteers

A Bioequivalence Study With Pharmacokinetic Endpoints for Azithromycin Eye Drops

Azithromycin eye drops with a bioadhesive ocular drug-delivery system can offer a simplified dosing regimen. In this study, we compared the pharmacokinetic properties and assessed the bioequivalence of a newly developed generic azithromycin eye drop with a branded formulation. This open-label, single-dose, randomized, crossover, sparse-sampling ocular bioequivalence study was conducted on 48 healthy Chinese volunteers. Tear samples were collected for up to 36 hours, and each participant was randomly allocated to one of the prespecified sampling times. Tear drug concentrations were determined using a validated liquid chromatography-tandem mass spectrometry method. The pharmacokinetic parameters were calculated via noncompartmental analysis. A nonparametric bootstrap method was used to obtain 90% confidence intervals (CIs) for the ratios of the test and reference drugs. Tolerability was evaluated for adverse events (AEs). After bootstrapping (1000 iterations), the 90%CIs for the log-transformed ratios of Cmax , AUC0-t , and AUC0-∞ were within the acceptable bioequivalence range (80%-125%). No moderate-to-severe AEs were reported for either formulation. Bioequivalence was demonstrated between the two formulations. The sparse-sampling design with the bootstrapping technique is promising for bioequivalence studies of topical ophthalmic drugs.

Strategies to prolong the residence time of drug delivery systems on ocular surface

Ocular diseases may be treated via different routes of administration, such as topical, intracameral, intravitreal, oral and parenteral. Among them the topical route is most accepted by patients, although it provides in many cases the lowest bioavailability. Indeed, when a topical formulation reaches the precorneal area, i.e., the drug absorption and/or action site, it is rapidly eliminated due to eye protection mechanisms such as blinking, basal and reflex tearing, and naso-lacrimal draining. To avoid this and to reduce the frequency of dosing, various strategies have been developed to prolong drug residence time after topical administration. These strategies include the use of viscosity increasing and mucoadhesive excipients as well as combinations thereof. From the drug delivery system point of view, liquid and semisolid formulations are preferred over solid formulations such as ocular inserts and contact lenses. Furthermore, liquid and semisolid formulations can contain nano- and microcarrier systems that contribute to a prolonged residence time. Within this review an overview about the different types of excipients and formulations as well as their performance in valid animal models and clinical trials is provided.

Population Pharmacokinetic Modeling of Azithromycin Eyedrops in Tears Following Single-Dose Topical Administration in Healthy Volunteers

BACKGROUND AND OBJECTIVES

The disposition of azithromycin in the human eye following topical administration has not been fully explored. Population pharmacokinetic (PopPK) modeling can allow useful conclusions to be drawn based on limited tear sampling data. The aim of this study was therefore to develop and evaluate a PopPK model of azithromycin eyedrops in tears, investigate typical model parameters, and identify potential covariates following single-dose ocular instillation.

METHODS

A total of 84 tear samples were obtained from 42 healthy volunteers at seven time points over 24 h following topical administration of azithromycin eyedrops (2.5 mL/25 mg). Azithromycin concentrations in the tears were determined using a validated LC-MS/MS assay. PopPK analysis was performed using nonlinear mixed-effects modeling. Intraocular pressure, tear secretion measurement, age, and gender were evaluated as possible covariates. Bootstrap and visual predictive checks were used simultaneously to evaluate the PopPK model. The dosage regimen was further estimated based on Monte Carlo simulation and the area under the curve/minimal inhibitory concentration.

RESULTS

A linear two-compartment first-order elimination model was found to best describe the pharmacokinetic profile of azithromycin in tears. None of the covariates had a significant influence on the typical model parameters. The final PopPK model was demonstrated to be suitable and effective according to bootstrap and visual predictive checks. Twice-daily instillation of azithromycin eyedrops would appear to provide the required antibacterial activity.

CONCLUSION

A proposed linear two-compartment PopPK model of azithromycin eyedrops was found to be effective at describing the disposition of azithromycin in tears after ocular instillation.

Ocular Drug Distribution After Topical Administration: Population Pharmacokinetic Model in Rabbits

BACKGROUND AND OBJECTIVE

When eye diseases are treated by topical administration, the success of treatment lies in the effective drug concentration in the target tissue. This is why the drug's pharmacokinetic, in the different substructures of the eye, needs to be explored more accurately during drug development. The aim of the present analysis was to describe by rabbit model, the distribution of a drug after ocular instillation in the selected eye tissues and fluids.

METHODS

By a top-down population approach, we developed and validated a population pharmacokinetics (PopPK) model, using tissue concentrations (tear, naso-lacrymal duct, cornea and aqueous humor) of a new src tyrosine kinase inhibitor (FV-60165) in each anterior segment's tissue and fluid of the rabbit eye. Inter-individual variability was estimated and the impact of the formulation (solution or nanosuspension) was evaluated.

RESULTS

The model structure selected for the eye is a 4-compartment model with the formulation as a significant covariate on the first-order rate constant between tears and the naso-lacrymal duct. The model showed a good predictive performance and may be used to estimate the concentration-time profiles after single or repeated administration, in each substructure of the eye for each animal included in the analysis.

CONCLUSIONS

This analysis allowed describing the distribution of a drug in the different selected tissues and fluids in the rabbit's eyes after instillation of the prodrug as a solution or nanosuspension.

Gender analysis of moxifloxacin clinical trials

PURPOSE

To determine the inclusion of women and the sex-stratification of results in moxifloxacin Clinical Trials (CTs), and to establish whether these CTs considered issues that specifically affect women, such as pregnancy and use of hormonal therapies. Previous publications about women's inclusion in CTs have not specifically studied therapeutic drugs. Although this type of drug is taken by men and women at a similar rate, adverse effects occur more frequently in the latter.

METHODS

We reviewed 158 published moxifloxacin trials on humans, retrieved from MedLine and the Cochrane Library (1998-2010), to determine whether they complied with the gender recommendations published by U.S. Food and Drug Administration Guideline.

RESULTS

Of a total of 80,417 subjects included in the moxifloxacin CTs, only 33.7% were women in phase I, in contrast to phase II, where women accounted for 45%, phase III, where they represented 38.3% and phase IV, where 51.3% were women. About 40.9% (n=52) of trials were stratified by sex and 15.3% (n=13) and 9% (n=7) provided data by sex on efficacy and adverse effects, respectively. We found little information about the influence of issues that specifically affect women. Only 3 of the 59 journals that published the moxifloxacin CTs stated that authors should stratify their results by sex.

CONCLUSIONS

Women are under-represented in the published moxifloxacin trials, and this trend is more marked in phase I, as they comprise a higher proportion in the other phases. Data by sex on efficacy and adverse effects are scarce in moxifloxacin trials. These facts, together with the lack of data on women-specific issues, suggest that the therapeutic drug moxifloxacin is only a partially evidence-based medicine.

Review of Azithromycin Ophthalmic 1% Solution (AzaSite(®)) for the Treatment of Ocular Infections

AzaSite(®) (azithromomycin 1.0%) ophthalmic solution was approved in 2007 by the US Food and Drug Administration (FDA) as the first commercially available formulation of ophthalmic azithromycin for the treatment of bacterial conjunctivitis. AzaSite(®) utilizes a vehicle delivery system called DuraSite(®), which stabilizes and sustains the release of azithromycin to the ocular surface, leading to a longer drug residence time, less frequent dosing, and an increase in patient compliance. AzaSite(®) is a broad spectrum antibiotic, effective against Gram-positive, Gram-negative, and atypical bacteria. AzaSite(®) has been studied for the treatment of ocular conditions beyond its clinical indication. A number of clinical studies have evaluated its efficacy and safety in the management of ocular conditions such as bacterial conjunctivitis and blepharitis on both the pediatric and adult populations. This article aims to evaluate the peer-reviewed published literature on the use of azithromycin 1.0% ophthalmic for current and possible future ophthalmic uses.

Update and critical appraisal of the use of topical azithromycin ophthalmic 1% (AzaSite) solution in the treatment of ocular infections

Azithromycin is an azalide that acts by binding to the 50S ribosomal subunit of susceptible microorganisms and interfering with microbial protein synthesis. Azithromycin is also noted by anti-inflammatory and immunomodulatory activity. AzaSite^® (Inspire Pharmaceuticals, Inc, Durham, NC) is azithromycin ophthalmic solution, 1% formulated in polycarbophil (the aqueous mucoadhesive polymer contained in DuraSite^®) that delivers high and prolonged azithromycin concentrations in a variety of ocular tissues, including the conjunctiva, cornea and particularly the eyelid. AzaSite was approved by the Food and Drug Administration (FDA) in the US in 2007, for the treatment of bacterial conjunctivitis caused by susceptible isolates. This article aims to evaluate the peer-reviewed published scientific literature and to define well-established uses of AzaSite eye drops in the field of ocular infections.

Pharmacokinetics of azithromycin and moxifloxacin in human conjunctiva and aqueous humor during and after the approved dosing regimens

PURPOSE

To evaluate the ocular pharmacokinetics of azithromycin and moxifloxacin in human conjunctiva and aqueous humor in subjects undergoing cataract surgery.

DESIGN

Multicenter, open-label, randomized study.

METHODS

Subjects scheduled for routine cataract surgery and with normal-appearing conjunctiva were eligible. One conjunctival biopsy sample and 1 aqueous humor sample were obtained from subjects randomly assigned to 1 of 10 prespecified time points (1 to 312 hours) after treatment initiation of azithromycin ophthalmic solution 1% or moxifloxacin ophthalmic solution 0.5%. Samples were assayed using liquid chromatography tandem mass spectrometry.

RESULTS

Azithromycin 1% provided high concentrations (peak level, 559.7 μg/g) in human conjunctiva that were sustained at levels 1 to 2 orders of magnitude higher than those of moxifloxacin 0.5% throughout the 7-day dosing period and for at least 7 days thereafter. Azithromycin also showed an extended half-life (65.7 hours) in conjunctiva relative to that of moxifloxacin (28.6 hours). Accordingly, the concentration of azithromycin was maintained well above the minimum inhibitory concentration required for inhibition of growth of 90% of tested bacterial isolates for at least 7 days, whereas moxifloxacin conjunctival levels fell to levels at or less than the minimum inhibitory concentration required for inhibition of growth of 90% of tested bacterial isolates approximately 24 hours after the last dose. Peak aqueous humor concentration of moxifloxacin was higher (0.77 μg/mL) than that of azithromycin (0.053 μg/mL). No clinically relevant safety findings were observed.

CONCLUSIONS

Azithromycin 1% demonstrated high, therapeutic levels in the conjunctiva that were maintained up to 7 days after completion of a 1-week dosing regimen. Aqueous humor levels, however, were subtherapeutic with this dosing regimen. In comparison, moxifloxacin achieved lower conjunctival tissue levels, but higher aqueous humor levels.

Azithromycin in DuraSite for the treatment of blepharitis

Blepharitis is a common inflammatory disease of the eyelid. Posterior blepharitis affects the posterior lamella of the eyelid and involves inflammation of the meibomian glands, whereas anterior blepharitis affects the anterior lamella of the eyelid and the eyelashes; either version can be inflammatory or infectious in nature. Each of these conditions can incite or propagate the other; anterior blepharitis, if not treated, can lead to meibomian gland disease, and vice versa. Blepharitis is typically chronic, and can be associated with a variety of systemic diseases such as dermatitis, as well as ocular diseases such as dry eye, conjunctivitis, or keratitis. The standard treatment regimen historically consists of lid hygiene with warm compresses and eyelid scrubs, although these treatment modalities may have limited efficacy for many patients, especially those with more severe disease. Adjunctive treatment includes systemic and topical antibiotics, topical corticosteroids, and tear replacement therapy. Topical antibiotics are recommended to decrease the bacterial load, and topical corticosteroids may help in cases of severe inflammation. Azithromycin ophthalmic solution 1% in DuraSite^® (AzaSite^®; Inspire Pharmaceuticals, Durham, North Carolina, USA) has been proposed as a novel treatment for posterior blepharitis, based on its well-known anti-infective profile, its anti-inflammatory properties, its excellent tissue penetration, and its regulatory approval for the treatment of bacterial conjunctivitis. This review focuses on an off-label indication for topical azithromycin 1% in DuraSite for the treatment of blepharitis.

Concentrations of besifloxacin, gatifloxacin, and moxifloxacin in human conjunctiva after topical ocular administration

PURPOSE

To evaluate the pharmacokinetic properties of besifloxacin, gatifloxacin, and moxifloxacin in the conjunctival tissue of healthy volunteers after topical application.

METHODS

One-hundred eight (108) subjects were randomly assigned to receive one drop of besifloxacin (0.6% suspension), gatifloxacin (0.3% solution), or moxifloxacin (0.5% solution) ophthalmic formulations in one eye prior to conjunctival biopsy. Conjunctival samples were taken from subjects at either 15 minutes, 30 minutes, 2 hours, 6 hours, 12 hours, or 24 hours after dosing.

RESULTS

All three fluoroquinolones reached a peak mean concentration 15 minutes after dosing. The mean concentrations of besifloxacin, gatifloxacin, and moxifloxacin at 15 minutes were 2.30 +/- 1.42 mug/g, 4.03 +/- 3.84 mug/g, and 10.7 +/- 5.89 mug/g, respectively. Concentrations decreased with each subsequent time point. At 24 hours after dosing, concentrations of besifloxacin were measurable in 4 of 6 subjects, compared with 3 of 6 subjects for gatifloxacin and 2 of 6 subjects for moxifloxacin. Besifloxacin had the greatest mean residence time (4.7 hours) in the conjunctival tissue. With regard to methicillin-resistant strains of Staphylococcus aureus and Staphylococcus epidermidis, besifloxacin had the greatest area-under-the-curve (AUC) to MIC(90) ratio. Nine percent (9%) of study subjects (N = 7) experienced a transient reduction in visual acuity.

CONCLUSION

All three fluoroquinolones were well tolerated and reached levels in the conjunctiva above the MIC(90)s of methicillin-sensitive S. aureus and S. epidermidis for at least 2 hours.