Physicochemical attributes and dissolution testing of ophthalmic ointments

Recent updates on ocular disease management with ophthalmic ointments

Ophthalmic diseases can result in permanent vision loss and blindness. Convenient topical and systemic treatments are preferred to address these sight-threatening conditions. However, the unique anatomy of the eye presents challenges for drug delivery. Various ophthalmic ointment formulations have been developed to enhance bioavailability in the eye to prolong residence time and improve corneal permeability. This article explores a wide range of ocular diseases affecting individuals globally and how ointments are used to manage them. From eye to ocular barriers, this review focuses on published scientific research and formulation strategies for severe ocular complications using conventional topical ointments. Additionally, it delves through patented technologies and marketed formulations supporting the use of ointments in ocular drug delivery.

Impact of active pharmaceutical ingredient variables and oleaginous base on the in vitro drug release from ophthalmic ointments: An investigation using dexamethasone as a model drug

The present study systematically investigates the impact of active pharmaceutical ingredient (API) variables and oleaginous base characteristics on the in vitro release (IVR) performance of ophthalmic ointments, utilizing dexamethasone as a model drug. The interplay between selected attributes (i.e., particle size distribution, crystallinity, and polymorphic form for API, and rheological factors for compendial-grade white petrolatum) and IVR performance was investigated. APIs from different vendors exhibited variations in crystallinity and polymorphism. Ointments containing amorphous dexamethasone presented higher release amounts/rates compared to crystalline counterparts, emphasizing the role of physical state in release kinetics. Variations in particle size of this lipophilic API (5.4 - 21.2 µm) did not appear to impact IVR performance significantly. In contrast, white petrolatum's rheological attributes, which varied substantially within USP-grade petrolatum, were found to critically affect the drug release rate and extent of the ointment. The study's comprehensive analysis establishes a coherent connection between the quality attributes of both API and petrolatum and IVR, delineating their intricate interdependent effects on ophthalmic ointment performance. These findings provide reference to formulation design, quality control, and regulatory considerations within the pharmaceutical industry, fostering a robust foundational understanding of commonly overlooked quality attributes in ophthalmic ointments.

Applications and Recent Developments of Hydrogels in Ophthalmology

Hydrogels are a type of functional polymer material with a three-dimensional network structure composed of physically or chemically cross-linked polymers. All hydrogels have two common features: first, their structure contains a large number of hydrophilic groups; therefore, they have a high water content and can swell in water. Second, they have good regulation, and the physical and chemical properties of their cross-linked network can be changed by environmental factors and deliberate modification methods. In recent years, the application of hydrogels in ophthalmology has gradually attracted attention. By selecting an appropriate composition and cross-linking mode, hydrogels can be used in different fields for various applications, such as gel eye drops, in situ gel preparation, intravitreal injection, and corneal contact lenses. This Review provides a detailed introduction to the classification of hydrogels and their applications in glaucoma, vitreous substitutes, fundus diseases, corneal contact lenses, corneal diseases, and cataract surgery.

Impact of Apparatus and Adapter on In vitro Drug Release of Ophthalmic Semisolid Drug Products

PURPOSE

In vitro release testing (IVRT) is a widely used tool for evaluating the quality and performance of drug products. However, standardized sample adaptors or drug release apparatus setups for IVRT studies are still lacking for ophthalmic ointments. The aim of this study was to provide a better understanding of the impact of apparatus and sample adaptor setups on IVRT of ophthalmic ointments.

METHODS

Dexamethasone (DEX), a steroidal ingredient commonly used in ophthalmic drug products, was selected as a model drug. Ointments were prepared by mixing DEX in white petrolatum using a high shear mixer. A novel two-sided adapter was developed to increase the drug release surface area. DEX ointment was placed in one-sided or two-sided release adaptors coupled with 1.2 μm polyethersulfone membrane, and the drug release was studied in different USP apparatuses (I, II, and IV).

RESULTS

The sample adaptor setups had a minimal impact on cumulative drug release amount per area or release rate while USP IV apparatus with agitated flow enhanced drug release rates. The USP apparatus I with a two-sided semisolid adapter, which uses membranes on both sides, showed dramatically higher cumulative drug release and discriminative release profiles when evaluating ophthalmic formulations.

CONCLUSIONS

USP apparatuses and sample adaptors are critical considerations for IVRT. Two-sided semisolid adapter provides higher cumulative release, facilitating the discrimination between low drug content ophthalmic ointment formulations with good sensitivity and repeatability without affecting the drug release rate.

Long-Acting Injectable Aqueous Suspensions-Summary From an AAPS Workshop

Through many years of clinical application of long-acting injectables, there is clear proof that this type of formulation does not just provide the patient with convenience, but more importantly a more effective treatment of the medication provided. The formulation approach therefore contains huge untapped potential to improve the quality of life of many patients with a variety of different diseases. This review provides a summary of some of the central talks provided at the workshop with focus on aqueous suspensions and their use as a long-acting injectable. Elements as formulation, manufacturing, in vitro dissolution methods, in vitro and in vivo correlation, in silico modelling provide an insight into some of the current understandings, learnings, and not least gaps in the field.

Advances in in-vitro bioequivalence testing methods for complex ophthalmic generic products

The United States Food and Drug Administration (USFDA) demands that the generic industry prove topical ocular products' pharmaceutical and bioequivalence (BE). In contrast to generic oral drugs, topical ocular product BE testing has proved difficult. New generic versions are compared to an authorized drug product known as a Reference Listed Drug (RLD) to demonstrate their bioequivalence. If the excellent in-vitro results may support the presumption of equivalence in-vivo performance and the only clinically significant difference between the generic and RLD is in its physicochemical qualities and drug release rate, then in-vivo BE studies may be waived. Proving BE through dissolution tests is a golden standard for most conventional dosage forms. However, due to the limited number of biorelevant in-vitro drug release testing (IVRT) approaches capable of differentiating their performance based on product quality and physicochemical properties, the development of generic ophthalmic products has been slow and time-consuming. Often, BE of topical ophthalmic formulations cannot be proved using a single in-vitro test; therefore, an elaborated discussion on various IVRT methods performed to demonstrate bioequivalence of complex generis like ophthalmic emulsions, suspensions, ointments, and gels is necessary. This manuscript aims to review the status of biowaiver criteria for complex ophthalmic products concerning the product-specific FDA guidance to the generic industry.

In vitro release testing method development for long-acting injectable suspensions

Long-acting injectable (LAI) suspensions are complex parenterals intended to control drug release over a duration of weeks to months. Any unpredictive drug release behavior may cause serious side effects. Therefore, it is important to understand the in vitro and in vivo performance, as well as the in vitro-in vivo correlation (IVIVC) of these products. There are some US FDA recommended in vitro release testing methods for LAI suspensions. However, the release duration of all the recommended methods is less than two days which may not be appropriate for the establishment of IVIVCs for LAIs considering that their in vivo efficacies range from weeks to months. To develop in vitro release testing methods that may better correlate with in vivo release with longer durations, three compositionally equivalent medroxyprogesterone acetate suspensions were prepared with different particle size, using Depo-SubQ Provera 104® as the reference listed drug (RLD). Four different methods based on USP apparatus 2 (with dialysis sacs, enhancer cells or in-house designed devices) and USP apparatus 4 (with semisolid adapters) were utilized. USP apparatus 2 with enhancer cells and USP apparatus 4 with semisolid adapters showed the best discriminatory ability and reproducibility for the LAI suspensions investigated.

Enhanced drug loading of in situ forming gels for oral mucositis pain control

Localized delivery to oral mucositis ulcerations requires specialized dosage forms, (e.g. in situ forming gels) delivered to the site in relatively low volumes. However, this is challenging for drugs with low solubility such as Bupivacaine γ-Linoleate (Bup-γL). The objective of this study is to develop an in situ forming gel with enhanced loading of Bup-γL for oral mucositis pain control. Two co-solvents (PEG400 and ethanol) and eight solubilizers (Tween 80, sodium lauryl sulfate, Cremophor® RH40, Cremophor® EL, Kolliphor® HS 15, Soluplus®, PEG 3350 and PEG8000) were screened for their capability to solubilize Bup-γL. Among all tested solubilizers, sodium lauryl sulfate (SLS) showed the highest solubilizing capacity (8.83 ± 0.94 mg/mL). This was considered to be a consequence of the similarity between the structure of SLS and Bup-γL. On the addition of SLS to the in situ forming gels, the drug loading was enhanced from ~6.5 to ~10.5 mg/ml. The formulations were characterized for their gelation temperature, rheological properties, in vitro drug release and short-term storage stability. The gelation temperatures of the in situ forming gel formulations were significantly reduced with enhanced drug loading. The in vitro drug release profiles showed good fit to both the first order and the Higuchi models. Formulations with SLS demonstrated sustained drug release (time to plateau ~7 h) compared with formulations without SLS (time to plateau ~3.5 h). This study offers an effective strategy to enhance drug loading of in situ forming gels. The enhanced drug loading will reduce the dosing volume and as such is expected to reduce any unwanted numbing of the healthy mucosa.

Impact of Membranes on In Vitro Release Assessment: a Case Study Using Dexamethasone

In vitro release studies are commonly used to assess the product performance of topical dosage forms. In such studies, the mass transport of drugs through synthetic membranes into a receiving chamber filled with a release medium is measured. The release medium is also passed through filtration membranes prior to chromatographic analysis. There are no official guidelines directing membrane selection for in vitro release studies or for filtration. Considering the diversity in membrane materials and their physical properties, the aim of this study was to investigate membrane-drug binding and the effect of various membranes on the release performance of a model drug dexamethasone (DEX) using USP dissolution apparatus IV. Seven membranes of different pore sizes (0.45 and 1.2 μm) and materials (cellulose acetate, polyethersulfone, and nylon) were assessed. Two different methods, syringe filter and 24-h incubation, were used for the determination of membrane-drug binding effects at low drug concentrations and saturated concentration conditions. Cellulose acetate and nylon membranes showed significant drug binding after 24-h incubations at both drug concentrations. DEX diffusion through membranes was significantly slowed down in all the tested membranes when compared with DEX solution without membranes. The extent of the retardation varied due to the differences in membrane structures. In conclusion, materials and sources of membranes affected drug dissolution profiles and the results showed membrane-drug binding effects. Proper selection of membranes with low drug binding ability and low diffusion resistance is essential to ensure appropriate and reproducible in vitro release assessments and filtration studies. Graphical Abstract.

Influence of Concentration on Release and Permeation Process of Model Peptide Substance-Corticotropin-From Semisolid Formulations

The transdermal route of administration of drug substances allows clinicians to obtain a therapeutic effect bypassing the gastrointestinal tract, where the active substance could be inactivated. The hormonal substance used in the study-corticotropin (ACTH)-shows systemic effects. Therefore, the study of the effect of the type of ointment base and drug concentration on the release rate and also permeation rate in in vivo simulated conditions may be a valuable source of information for clinical trials to effectively optimize corticotropin treatment. This goal was achieved by preparation ointment formulation selecting the appropriate ointment base and determining the effect of ACTH concentration on the release and permeation studies of the ACTH. Semi-solid preparations containing ACTH were prepared using Unguator CITO e/s. The release study of ACTH was tested using a modified USP apparatus 2 with Enhancer cells. The permeation study was conducted with vertical Franz cells. Rheograms of hydrogels were made with the use of a universal rotational rheometer. The dependence of the amount of released and permeated hormone on the ointment concentration was found. Based on the test of ACTH release from semi-solid formulations and evaluation of rheological parameters, it was found that glycerol ointment is the most favourable base for ACTH. The ACTH release and permeation process depends on both viscosity and ACTH concentration. The higher the hormone concentration, the higher the amount of released ACTH but it reduces the amount of ACTH penetrating through porcine skin.

In Situ Gelling Ophthalmic Drug Delivery System for the Optimization of Diagnostic and Preoperative Mydriasis: In Vitro Drug Release, Cytotoxicity and Mydriasis Pharmacodynamics

Mydriasis is required prior to many eye examinations and ophthalmic surgeries. Nowadays, phenylephrine hydrochloride (PHE) and tropicamide (TPC) are extensively used to induce mydriasis. Several pharmaceutic dosage forms of these two active ingredients have been described. However, no optimal therapeutic strategy has reached the market. The present work focuses on the formulation and evaluation of a mucoadhesive ion-activated in situ gelling delivery system based on gellan gum and hydroxyethylcellulose (HEC) for the delivery of phenylephrine and tropicamide. First, in vitro drug release was studied to assess appropriate sustained drug delivery on the ocular surface region. Drug release mechanisms were explored and explained using mathematical modeling. Then, in situ gelling delivery systems were visualized using scanning electron microscopy illustrating the drug release phenomena involved. Afterward, cytotoxicity of the developed formulations was studied and compared with those of commercially available eye drops. Human epithelial corneal cells were used. Finally, mydriasis intensity and kinetic was investigated in vivo. Mydriasis pharmacodynamics was studied by non-invasive optical imaging on vigilant rabbits, allowing eye blinking and nasolacrimal drainage to occur physiologically. In situ gelling delivery systems mydriasis profiles exhibited a significant increase of intensity and duration compared with those of conventional eye drops. Efficient mydriasis was achieved following the administration of a single drop of in situ gel reducing the required amount of administered active ingredients by four- to eight-fold compared with classic eye drop regimen.

Impact of product design parameters on in vitro release from intrauterine systems

Polydimethylsiloxane (PDMS)-based levonorgestrel intrauterine systems (LNG-IUSs) contain a large amount of potent LNG, and therefore it is important to understand the impact of product design parameters on the in vitro and in vivo performance to ensure safety and efficacy, as well as to avoid serious side effects resulting from dose dumping. LNG-IUS is a complex drug-device combination product, and its formulation design, requires consideration of additional factors such as device configuration and dimensions, in addition to formulation and processing parameters. In this study, ten qualitatively (Q1) and quantitatively (Q2) equivalent LNG-IUSs were manufactured with differences in source (supplier) and dimensions (i.e., thickness) of the outer membrane, drug particle size, dimensions of the drug reservoir (i.e., inner diameter), as well as configuration of the entire IUS. A real-time in vitro release testing method was developed for the LNG-IUSs. In addition, an accelerated release testing method was developed using hydro-alcoholic media in order to reduce the time associated with formulation design. Source variations and thickness of their outer membranes had a great impact on the in vitro drug release from the LNG-IUSs. It was demonstrated that the thicker the outer membrane, the slower the drug release rate. The physicochemical properties of the outer membranes obtained from different sources were characterized to understand their impact on the in vitro drug release of the LNG-IUSs. The composition and mechanical strength may play a role in differences in drug release. The LNG-IUS formulation prepared with the larger drug particle size showed a slightly slower daily release rate. The drug release rates from the compositionally equivalent LNG-IUSs linearly correlated to the surface area of the corresponding drug reservoirs. Another factor that affected the drug release rate was the configuration of the entire IUS. It was shown that the placement of the outer membrane was significant, i.e. whether the ends of the drug reservoir were covered or not. It is important to note that real-time release showed zero-order release kinetics over the test period of approximately 900 days. The current study provides a comprehensive understanding of the impact of product design parameters on the in vitro drug release of LNG-IUSs. In addition, the developed real-time and accelerated release testing methods showed good discriminatory ability for compositionally equivalent LNG-IUSs prepared using different product design parameters.

Hydrogel Biomaterials for Application in Ocular Drug Delivery

There are many challenges involved in ocular drug delivery. These are a result of the many tissue barriers and defense mechanisms that are present with the eye; such as the cornea, conjunctiva, the blinking reflex, and nasolacrimal drainage system. This leads to many of the conventional ophthalmic preparations, such as eye drops, having low bioavailability profiles, rapid removal from the administration site, and thus ineffective delivery of drugs. Hydrogels have been investigated as a delivery system which is able to overcome some of these challenges. These have been formulated as standalone systems or with the incorporation of other technologies such as nanoparticles. Hydrogels are able to be formulated in such a way that they are able to change from a liquid to gel as a response to a stimulus; known as "smart" or stimuli-responsive biotechnology platforms. Various different stimuli-responsive hydrogel systems are discussed in this article. Hydrogel drug delivery systems are able to be formulated from both synthetic and natural polymers, known as biopolymers. This review focuses on the formulations which incorporate biopolymers. These polymers have a number of benefits such as the fact that they are biodegradable, biocompatible, and non-cytotoxic. The biocompatibility of the polymers is essential for ocular drug delivery systems because the eye is an extremely sensitive organ which is known as an immune privileged site.

Drug release testing of long-acting intrauterine systems

Performance evaluation of polydimethylsiloxane (PDMS) based long-acting (e.g. 3-5 years) levonorgestrel (LNG) intrauterine systems (IUSs), such as Mirena®, is challenging due to their complex formulation, locally-acting feature, and extremely long duration of drug release. To achieve such long-term release, a large amount of drug (up to 52 mg in Mirena®) must be incorporated as a drug reservoir in the IUS. Consequently, dose dumping or unanticipated changes in the LNG-IUS in vivo release characteristics may give rise to adverse product safety and efficacy. Therefore, it is crucial to understand, and have appropriate control over, the physicochemical properties and in vitro release characteristics of these products. This requires an understanding of the LNG-IUSs drug release mechanism and the development of a sensitive yet robust in vitro release testing method. There have been no previous reports on in vitro drug release and the release mechanism from LNG-IUSs. This is probably a consequence of the extremely slow drug release rate of LNG-IUSs under real-time in-use conditions (e.g., 3-5 years) and therefore it is impractical to obtain complete release profiles (e.g. there is only 60% release in 5 years for Mirena®). Therefore, the development of appropriate accelerated in vitro release methods is imperative. Following preparation of LNG-IUSs, similar to Mirena®, real-time release was tested in (0.9% w/v NaCl) media in a water shaker bath at 37 °C for over 2 years. Addition of surfactant (sodium dodecyl sulfate (SDS)), elevation of temperature, addition of organic solvents (ethanol (EtOH), isopropanol (IPA), tert-butanol (TBA) and tetrahydrofuran (THF)) and a combination thereof were utilized as release media to accelerate drug release for LNG-IUSs. Complete drug release was achieved in 32 and 672 days in THF and TBA hydro-organic media, respectively. The release profile in THF was considered too fast as it may result in change of release mechanism, whereas the release profile in TBA was deemed suitable following model fitting. Model fitting was performed to understand the release characteristics as well as the release mechanisms. The release rate in the hydro-alcoholic media was linearly proportional to the swelling ratio of the PDMS in the corresponding organic solvents. Zero-order, first-order and two-phase models were utilized to fit the release profiles obtained under the different release conditions. The data analysis was comparable using the parameters from different models given the high R² values. However, the two-phase model was better in terms of the release mechanism of the LNG-IUSs considering the full drug release profile. The present study will facilitate the process of granting of biowaivers through an in vitro approach, thus reducing the necessity for clinical studies. In addition, it will help reduce the regulatory burden without sacrificing product quality of LNG-IUS products.

Novel in situ gelling ophthalmic drug delivery system based on gellan gum and hydroxyethylcellulose: Innovative rheological characterization, in vitro and in vivo evidence of a sustained precorneal retention time

Achieving drug delivery at the ocular level encounters many challenges and obstacles. In situ gelling delivery systems are now widely used for topical ocular administration and recognized as a promising strategy to improve the treatment of a wide range of ocular diseases. The present work describes the formulation and evaluation of a mucoadhesive and ion-activated in situ gelling delivery system based on gellan gum and hydroxyethylcellulose for the delivery of phenylephrine and tropicamide. First, physico-chemical characteristics were assessed to ensure suitable properties regarding ocular administration. Then, rheological properties such as viscosity and gelation capacity were determined. Gelation capacity of the formulations and the effect of hydroxyethylcellulose on viscosity were demonstrated. A new rheological method was developed to assess the gel resistance under simulated eye blinking. Afterward, mucoadhesion was evaluated using tensile strength test and rheological synergism method in both rotational and oscillatory mode allowing mucoadhesive properties of hydroxyethylcellulose to be point out. Finally, residence time on the ocular surface was investigated in vivo, using cyanine 5.5 dye as a fluorescent marker entrapped in the in situ gelling delivery systems. Residence performance was studied by non-invasive optical imaging on vigilant rabbits, allowing eye blinking and nasolacrimal drainage to occur physiologically. Fluorescence intensity profiles pointed out a prolonged residence time on the ocular surface region for the developed formulations compared to conventional eye drops, suggesting in vitro / in vivo correlations between rheological properties and in vivo residence performances.

Advances in Biodegradable Nano-Sized Polymer-Based Ocular Drug Delivery

The effective delivery of drugs to the eye remains a challenge. The eye has a myriad of defense systems and physiological barriers that leaves ocular drug delivery systems with low bioavailability profiles. This is mainly due to poor permeability through the epithelia and rapid clearance from the eye following administration. However, recent advances in both polymeric drug delivery and biomedical nanotechnology have allowed for improvements to be made in the treatment of ocular conditions. The employment of biodegradable polymers in ocular formulations has led to improved retention time, greater bioavailability and controlled release through mucoadhesion to the epithelia in the eye, amongst other beneficial properties. Nanotechnology has been largely investigated for uses in the medical field, ranging from diagnosis of disease to treatment. The nanoscale of these developing drug delivery systems has helped to improve the penetration of drugs through the various ocular barriers, thus improving bioavailability. This review will highlight the physiological barriers encountered in the eye, current conventional treatment methods as well as how polymeric drug delivery and nanotechnology can be employed to optimize drug penetration to both the anterior and posterior segment of the eye.

Innovation for Generic Drugs: Science and Research Under the Generic Drug User Fee Amendments of 2012

Regulatory science is science and research intended to improve decision making in a regulatory framework. Improvements in decision making can be in both accuracy (making better decisions) and in efficiency (making faster decisions). Science and research supported by the Generic Drug User Fee Amendments of 2012 (GDUFA) have focused on two innovative methodologies that work together to enable new approaches to development and review of generic drugs: quantitative models and advanced in vitro product characterization. Quantitative models faithfully represent current scientific understanding. They are tools pharmaceutical scientists and clinical pharmacologists use for making better and faster product development decisions. Advances in the in vitro product comparisons provide the measurements of product differences that are the critical input into the models. This paper outlines four areas where science and research funded by GDUFA support synergistic use of models and characterization at critical decision points during generic drug product development and review.

Tobramycin/dexamethasone eye drops as a better choice for lacrimal duct probing in persistent congenital nasolacrimal duct obstruction: A consort study

BACKGROUND

Congenital nasolacrimal duct obstruction (CNLDO) is common and. lacrimal duct probing is the major treatment. But persistent CNLDO in older children makes the success rate rapidly decreased due to long-term chronic inflammation. To improve the success rate, probing combined with tobramycin/dexamethasone ointment is considered effective. But in practice, we found a lot of problems in using the ointment. So we tried tobramycin/dexamethasone eye drops as a replacement. The results is surprising, so we hope to do some further research in order to prove it is worth to clinical application.

OBJECTIVE

To evaluate the effect of lacrimal duct probing combined with tobramycin/dexamethasone eye drops or ointment on persistent CNLDO in children older than 1-year-old.

METHODS

This randomized controlled study included 409 subjects (496 eyes) older than 1-year-old with persistent CNLDO in southwest China, and classified into 3 groups: 96 cases (123 eyes) were the tobramycin/dexamethasone eye drops group (drops group), 88 cases (104 eyes) were the tobramycin/dexamethasone ointment group (ointment group), and 225 cases (269 eyes) were control group which probing with normal saline (NS group). The data of age, sex, and laterality were analyzed through pairwise comparison. Then the 3 groups were divided into 2 subgroups by age, 12 to 24 months and 25 to 36 months. The surgical findings and success rate in two subgroups were compared.

RESULTS

The success rates in the tobramycin/dexamethasone eye drops group in both 2 age subgroups were significantly higher than that in the ointment group and NS group (P < .05).

CONCLUSIONS

Probing combined with tobramycin/dexamethasone eye drops was effective and easy-to-perform in the clinic, and it may be a better choice for persistent CNLDO.

Perspectives on Physicochemical and In Vitro Profiling of Ophthalmic Ointments

Ophthalmic ointments are unique in that they combine features of topical drug delivery, the ophthalmic route and ointment (semisolid) formulations. Accordingly, these complex formulations are challenging to develop and evaluate and therefore it is critically important to understand their physicochemical properties as well as their in vitro drug release characteristics. Previous reports on the characterization of ophthalmic ointments are very limited. Although there are FDA guidance documents and USP monographs covering some aspects of semisolid formulations, there are no FDA guidance documents nor any USP monographs for ophthalmic ointments. This review summarizes the physicochemical and in vitro profiling methods that have been previously reported for ophthalmic ointments. Specifically, insight is provided into physicochemical characterization (rheological parameters, drug content and content uniformity, and particle size of the API in the finished ointments) as well as important considerations (membranes, release media, method comparison, release kinetics and discriminatory ability) in in vitro release testing (IVRT) method development for ophthalmic ointments. Graphical Abstract Summary of the physicochemcial profiling and in vitro drug release testing (IVRT) for ophthalmic ointments.

Formulation characteristics and in vitro release testing of cyclosporine ophthalmic ointments

The aim of the present study was to investigate the relationship between formulation/process variables versus the critical quality attributes (CQAs) of cyclosporine ophthalmic ointments and to explore the feasibility of using an in vitro approach to assess product sameness. A definitive screening design (DSD) was used to evaluate the impact of formulation and process variables. The formulation variables included drug percentage, percentage of corn oil and lanolin alcohol. The process variables studied were mixing temperature, mixing time and the method of mixing. The quality and performance attributes examined included drug assay, content uniformity, image analysis, rheology (storage modulus, shear viscosity) and in vitro drug release. Of the formulation variables evaluated, the percentage of the drug substance and the percentage of corn oil in the matrix were the most influential factors with respect to in vitro drug release. Conversely, the process parameters tested were observed to have minimal impact. An evaluation of the release mechanism of cyclosporine from the ointment revealed an interplay between formulation (e.g. physicochemical properties of the drug and ointment matrix type) and the release medium. These data provide a scientific basis to guide method development for in vitro drug release testing of ointment dosage forms. These results demonstrate that the in vitro methods used in this investigation were fit-for-purpose for detecting formulation and process changes and therefore amenable to assessment of product sameness.

In vitro and ex vivo correlation of drug release from ophthalmic ointments

In vitro drug release testing and ex vivo transcorneal drug permeation can provide valuable information on the performance of the Q1/Q2 equivalent ointments prior to any animal studies. Good correlation between in vitro and ex vivo drug release may be indicative of good in vitro and in vivo correlation. Accordingly, it is important to investigate in vitro as well as ex vivo drug release from Q1/Q2 equivalent ophthalmic ointments and evaluate whether a correlation between these release profiles can be established. Four Q1/Q2 equivalent loteprednol etabonate ointments were prepared using different processing methods and excipient sources. The rheological parameters (crossover modulus and K value) of the four formulations were determined. The in vitro drug release testing of the four ointment formulations were performed using three different apparati (Franz diffusion cells, USP apparatus 2 with enhancer cells and USP apparatus 4 with semisolid adapters). Three models (zero order, logarithmic and the Higuchi model) were used to study the release kinetics of the ointment formulations. The transcorneal (rabbit corneas) permeation studies were performed using spherical joint Franz diffusion cells. The USP apparatus 4 method demonstrated better discriminatory ability compared to the USP apparatus 2 and the Franz diffusion cell methods. The in vitro release profiles of the four Q1/Q2 equivalent ointments with manufacturing differences showed a better fit using the Higuchi model (R² > 0.98) for all three release testing methods, compared to the other two models. Ex vivo drug release through the rabbit corneas displayed zero order release kinetics. A logarithmic correlation between rheological parameters (crossover and K value) and transcorneal flux were established. In addition, a plot of the in vitro release rate against the ex vivo release flux of the four ointment formulations, yielded a straight line (R² > 0.98) for all three release methods. Accordingly, the rheological parameters may be useful in predicting in vitro as well as ex vivo release properties.

In vitro release testing method development for ophthalmic ointments

It is essential as well as challenging to develop a reliable in vitro release testing method for determining whether differences in release profiles exist between qualitatively and quantitatively equivalent ophthalmic ointment formulations. There is a lack of regulatory guidance on in vitro release testing methods for ophthalmic formulations. Three different in vitro release testing methods 1) USP apparatus 4 with semisolid adapters; 2) USP apparatus 2 with enhancer cells; and 3) Franz diffusion cells were investigated. Qualitatively and quantitatively equivalent ointments were prepared via hot melting and simple mixing methods using four different sources of excipients (i.e. white petrolatum). The ointment formulations were characterized for content uniformity, particle size, and rheological parameters. All the formulations showed adequate content uniformity and similar particle size. The ointments prepared via the hot melting processes showed higher rheological parameters, as did the ointments prepared using 'white' petrolatum that exhibited a yellowish color. The three in vitro release testing methods were compared and evaluated for reproducibility, discriminatory capability, and correlation with the rheological parameters. Compared with the compendial methods, the non-compendial method (Franz diffusion cells) showed poorer reproducibility. All three methods possessed the ability to discriminate between the ophthalmic ointments with manufacturing differences. However, the USP apparatus 4 method displayed the largest margin of discrimination between the release profiles of the different ophthalmic ointments. In addition, the in vitro release rate obtained using the USP apparatus 4 method showed the strongest logarithmic linear correlation with the rheological parameters (Power law consistency index (K value) and crossover modulus) compared to the other two methods.