Pluronic F127-based ocular delivery system containing biodegradable polyisobutylcyanoacrylate nanocapsules of pilocarpine

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.

A Critical Sojourn of Polymeric Micelles: Technological Concepts, Recent Advances, and Future Prospects

Poorly soluble drug molecules/phytoconstituents are still a growing concern for biopharmaceutical delivery in the body. Polymeric micelles are the amphiphilic block copolymers and have been widely investigated as targeted nanocarriers for the treatment of various ailments. The versatility of nanocarriers is the self-assembling properties in the aqueous medium and forms a stable isotropic system in vivo. The hydrophobic core-hydrophilic shell configuration of the polymers used to the mixed micelles makes easy encapsulation of hydrophobic and hydrophilic drugs into the core. Polymeric micelles can also be combined with targeting ligands that increase their uptake by specific cells, decreasing off-target effects, and provide enhanced therapeutic effect. In the present review, we primarily focused on a critical appraisal of Polymeric micelles along with the method of preparation, mechanism of micelle formulation, and the ongoing formulations under clinical trials. In addition, the biological applications of this isotropic nanocarrier have been duly presented in each route of administration along with suitable case studies.

A Review on Newer Ocular Drug Delivery Systems with an Emphasis on Glaucoma

Glaucoma is an irreversible condition resulting from the increase in intraocular pressure (IOP); which leads to permanent loss of vision with the destruction of retinal ganglion cells (RGCs). The IOP elevations are controlled in normal by the physiological flow of aqueous humour. A population with age above 40 is more susceptible to glaucoma. Other factors like gender, genetics, race etc. plays major roles in the development of the disease. Current treatment methods available for the disease includes drugs come under the classes of beta receptor blockers, carbonic anhydrase inhibitors, cholinergic agonists, prostaglandins etc. N-methyl-D-aspartate (NMDA) antagonists, inducible nitric oxide synthase (iNOS) inhibition, cytoskeletal agents, Rho-kinase inhibitors etc are few novel targets sites which are in research focus for the treatment of the disease. Developments in nanomedicine are also being evaluated for their potential in treating the growing glaucomatous population. Nanosystems are suggested to avoid the difficulties in tackling the various ocular barriers to a limit, help to decrease the instillation frequency of topical medication and can provide drug delivery in a sustained or controlled manner. This review focuses on the current and emerging treatment methods for glaucoma along with some of the nanoformulations for ocular drug delivery.

Cyclosporine Lipid Nanocapsules as Thermoresponsive Gel for Dry Eye Management: Promising Corneal Mucoadhesion, Biodistribution and Preclinical Efficacy in Rabbits

An ophthalmic cyclosporine (CsA) formulation based on Lipid nanocapsules (LNC) was developed for dry eye management, aiming to provide targeting to ocular tissues with long-term drug levels and maximum tolerability. CsA-LNC were of small particle size (41.9 ± 4.0 nm), narrow size distribution (PdI ≤ 0.1), and high entrapment efficiency (above 98%). Chitosan (C) was added to impart positive charge. CsA-LNC were prepared as in-situ gels using poloxamer 407 (P). Ex vivo mucoadhesive strength was evaluated using bovine cornea, while in vivo corneal biodistribution (using fluorescent DiI), efficacy in dry eye using Schirmer tear test (STT), and ocular irritation using Draize test were studied in rabbits compared to marketed ophthalmic CsA nanoemulsion (CsA-NE) and CsA in castor oil. LNC incorporation in in-situ gels resulted in an increase in mucoadhesion, and stronger fluorescence in corneal layers seen by confocal microscopy, compared to the other tested formulations. Rate of recovery (days required to restore corneal baseline hydration level) assessed over 10 days, showed that CsA-LNC formulations produced complete recovery by day 7 comparable to CsA-NE. No Ocular irritation was observed by visual and histopathological examination. Based on data generated, CsA-LNC-CP in-situ gel proved to be a promising effective nonirritant CsA ophthalmic formulation for dry eye management.

Evaluation of His6-Metal Assemblies as a Drug Delivery Vehicle in the Treatment of Anterior Segment Disease Using a Corneal Inflammation Model

Keratitis is a common ophthalmological disease and also a common cause of blindness (second only to cataracts). This disease is routinely treated by topical administration of dexamethasone sodium phosphate (Dexp). However, due to the presence of anatomical and physiological barriers, frequent administration is needed, often resulting in poor patient compliance and diverse side effects. In this work, Dexp was in situ encapsulated into a His₆-metal assembly (HmA) to generate Dexp@HmA, which was utilized in the ocular delivery of Dexp. The physicochemical properties of HmA and Dexp@HmA particles were characterized in detail using various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV-vis spectroscopy. Compared to commercial Eudragi and reported PLGA nanoparticles, HmA showed higher encapsulation efficiency (EE%) and higher loading capacity (LC wt %) of Dexp. Dexp@HmA displayed pH-dependent release; after 33 days at pH 5.8, 6.5, and 7.2, 100%, 65%, and 42% of Dexp, respectively, had been released. In addition, HmA and Dexp@HmA showed low cytotoxicity to macrophages and to all common ocular cell types tested. The effect of Dexp@HmA on corneal inflammation was evaluated using in vitro and in vivo models. Our results demonstrate that Dexp@HmA is much superior to free Dexp in both in vitro and in vivo models. These positive results suggest that HmA may represent a promising candidate nanocarrier for the treatment of various diseases of the anterior segment of the eye.

Exploring the mucoadhesive behavior of sucrose acetate isobutyrate: a novel excipient for oral delivery of biopharmaceuticals

Oral drug delivery is an attractive noninvasive alternative to injectables. However, oral delivery of biopharmaceuticals is highly challenging due to low stability during transit in the gastrointestinal tract (GIT), resulting in low systemic bioavailability. Thus, novel formulation strategies are essential to overcome this challenge. An interesting approach is increasing retention in the GIT by utilizing mucoadhesive biomaterials as excipients. Here, we explored the potential of the GRAS excipient sucrose acetate isobutyrate (SAIB) to obtain mucoadhesion in vivo. Mucoadhesive properties of a 90% SAIB/10% EtOH (w/w) drug delivery system (DDS) were assessed using a biosimilar mucus model and evaluation of rheological behavior after immersion in biosimilar intestinal fluid. To ease readability of this manuscript, we will refer to this as SAIB DDS. The effect of SAIB DDS on cell viability and epithelial membrane integrity was tested in vitro prior to in vivo studies that were conducted using SPECT/CT imaging in rats. When combining SAIB DDS with biosimilar mucus, increased viscosity was observed due to secondary interactions between biosimilar mucus and sucrose ester predicting considerable mucoadhesion. Mucoadhesion was confirmed in vivo, as radiolabeled insulin entrapped in SAIB DDS, remained in the small intestine for up to 22 h after administration. Moreover, the integrity of the system was investigated using the dynamic gastric model under conditions simulating the chemical composition of stomach fluid and physical shear stress in the antrum under fasted conditions. In conclusion, SAIB is an interesting and safe biomaterial to promote high mucoadhesion in the GIT after oral administration.

Poloxamer-based in situ gelling thermoresponsive systems for ocular drug delivery applications

In situ gels have recently received interest as ocular drug delivery vehicles because they combine the merits of easy instillation and sustained drug release. In this review, we focus on the use of poloxamers as in situ gelling systems in ocular drug delivery because of their thermoresponsive gelling behaviour, biocompatibility, and ease of sterilisation. Furthermore, the sol-gel transition temperature, mucoadhesive properties, and drug release profiles of poloxamer-based in situ gels can be finely tuned, enabling them to be used as vehicles for the delivery of small and large drug molecules to treat diseases of the anterior and posterior segments of the eye. Poloxamer-based ocular products have already found their way to the pharmaceutical market, but remain a potential arena for further investigation and commercial exploitation.

Cross-linked hyaluronan films loaded with acetazolamide-cyclodextrin-triethanolamine complexes for glaucoma treatment

AIM

This work aimed to design and characterize cross-linked hyaluronic acid-itaconic acid films loaded with acetazolamide-hydroxypropyl β cyclodextrin-triethanolamine complexes.

MATERIALS & METHODS

Films were cross-linked with itaconic acid and poly(ethyleneglycol)-diglycidylether. Biopharmaceutical properties were assessed by evaluating in vitro drug release rate, biocompatibility in a human corneal epithelial cell line, bioadhesiveness with pig gastric mucin, in vivo bioadhesion and efficacy.

RESULTS

Showed good mechanical properties and oxygen permeability. Proliferation rate of corneal cells was affected by highest acetazolamide concentration. Bioadhesive interaction exhibited a water movement from pig mucin to the film; in vivo experiments showed strong bioadhesion for 8 h and hypotensive effect for almost 20 h.

CONCLUSION

Experimental set showed promising performance and encouraged future studies to optimize formulation. [Formula: see text].

A combined therapy of rtPA-loaded thermoresponsive gels and ultrasound on hematoma in a rat model of intracerebral hemorrhage

To develop and validate an effective method for the removal of residual intracerebral hematoma, we prepared a recombinant tissue-type plasminogen activator (rtPA)-loaded Pluronic F127 (NP-rtPA) delivery system to evaluate the neurological response of the ICH rat model.

Gel formulations containing catanionic vesicles composed of alprenolol and SDS: effects of drug release and skin penetration on aggregate structure

To fully utilize the extended contact time of gel formulations a novel formulation with drug containing catanionic aggregates offering prolonged drug release and skin penetration were investigated. This study aimed to further explore the drug release process from catanionic vesicles in gels. Catanionic vesicles were formed from alprenolol and sodium dodecyl sulphate. Physical gels composed of catanionic vesicles and a SoftCAT polymer were used as well as covalent Carbopol gels. Drug release was measured in vitro using a modified USP paddle method and the skin penetration was studied using dermatomized pig ear skin mounted in horizontal Ussing chambers. The aggregate structure was visualized with cryo-TEM during the drug release and skin penetration process. The study results show that catanionic vesicles are present in the formulations throughout the drug release process and during the clinically relevant skin application time. Hence, the decreased skin penetration rate stems from the prolonged release of drug substance from the gels. The rheological investigation shows that the gel structure of the physically cross-linked gels is maintained even as the drug substance is released and the gel volume is decreased. These findings indicate that the applicability of formulations like these is a future possibility.

Advancements in ocular drug delivery

This review covers both noninvasive and invasive ophthalmic drug delivery systems that can have application to therapy of veterinary ophthalmic diseases. Noninvasive approaches include gel technologies, permeation enhancement via pro-drug development, solubilization agents and nanoparticle technologies, iontophoresis, microneedles, drug-eluting contact lenses and eye misters, and microdroplets. More invasive systems include both eroding implants and noneroding technologies that encompass diffusion based systems, active pumps, intraocular lenses, suprachoroidal drug delivery, and episcleral reservoirs. In addition to addressing the physiologic challenges of achieving the necessary duration of delivery, tissue targeting and patient compliance, the commercial development factors of biocompatibility, sterilization, manufacturability and long-term stability will be discussed.

Eudragit RL100 nanoparticle system for the ophthalmic delivery of cloricromene

A Eudragit RL100 polymer nanoparticle system loaded with cloricromene was prepared and characterized on the basis of physicochemical properties, stability and drug release features. To investigate the ocular bioavailability of cloricromene after inclusion in the polymer matrix, the new nanoparticle system was topically administered in the rabbit eye and compared with an aqueous solution of the same drug. The nanoparticle system showed interesting size distribution and surface charge values, suitable for ophthalmic application. The results indicated that the dispersion of cloricromene within Eudragit RL100 polymer nanoparticles increased its ocular bioavailability and enhanced the biopharmaceutical profile. The new cloricromene-loaded nanoparticle system described here may be useful in clinical practice.

Poly (epsilon-caprolactone) microparticles containing Levobunolol HCl prepared by a multiple emulsion (W/O/W) solvent evaporation technique: effects of some formulation parameters on microparticle characteristics

The aim of this study was to prepare poly (epsilon-caprolactone) (PCL) microparticles of Levobunolol HC1 (L-HC1) for use as an anti-glaucomatous drug to the eye. The double emulsion (W/O/W) solvent evaporation technique was used for encapsulating L-HC1 as a hydrophilic drug. The study examined the impact of different factors including the pH and volume of the external aqueous phase, the concentration of polyvinylalcohol (PVA) and Pluronic F68 (PF68) used as stabilizers and drug/polymer ratios on the characteristics of the microparticles. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to identify the physical state of the drug and polymer. The zeta potential of the particles was also identified. Entrapment efficiency was found to be highest with a 0.5% PVA concentration and 100 mL volume of external aqueous phase at pH 12. The high efficiency was due to a reduction in the degree of drug ionization. The microparticles were spherical and appropriately sized for ophthalmic application. Drug release from the microparticles appears to consist of two components, with an initial rapid release followed by a slower stage. Drug release was slower when the microparticle was incorporated into the thermally reversible gel (Pluronic F127) in comparison to drug release from the free drug incorporated into the gel and drug release from the free microparticle.

Acyclovir liposomes for intranasal systemic delivery: development and pharmacokinetics evaluation

Intranasal route is one of the most attractive routes for distributing drugs to systemic circulation. Liposomes are used as biocompatible carriers to improve delivery properties across nasal mucosa. The objective of the present study was to formulate acyclovir liposomes and partition into poly-N-vinyl-2-pyrrolidone. Entrapment efficiency showed that multilamellar and unilamellar liposomes were 43.2% +/- 0.83 and 21% +/- 1.01, respectively. The bioavailability of acyclovir from nasal mucoadhesive gel was 60.72% compared with intravenous route. The use of liposomes acyclovir and mucoadhesive gel not only promoted the prolonged contact between the drug and the absorptive sites in the nasal cavity, but also facilitated direct absorption through the nasal mucosa.

Eudragit® microparticles as a possible tool for ophthalmic administration of acyclovir

This paper describes the production and characterization of polyacrylic polymer (Eudragit RL, RS and NE) microparticles by spray drying method. Microparticles were designed for ophthalmic administration of acyclovir. Microparticle morphology was characterized by optical and electron microscopy. The release kinetics of the drug from microspheres were determined by a dialysis method. The spray drying method described allows the production of microparticles with acceptable encapsulation efficiency and appropriate dimensional characteristics for ophthalmic administration. Release profile data indicate that acyclovir is released from microparticles in a controlled manner. In addition the release pattern of the drug is influenced by the type of Eudragit used for microparticle production. Moreover the plaque reduction efficiency of acyclovir containing microparticles (except for RS/NE microspheres) is comparable to that displayed by the free drug. Finally our results suggest that acyclovir containing microparticles could represent an interesting system for the release of this antiviral drug at the eye site.

Compatibility of human fetal neural stem cells with hydrogel biomaterials in vitro

Stroke and spinal cord or brain injury often result in cavity formation. Stem cell transplantation in combination with tissue engineering has the potential to fill such a cavity and replace lost neurons. Several hydrogels containing unique features particularly suitable for the delicate nervous system were tested by determining whether these materials were compatible with fetal human neural stem cells (hNSCs) in terms of toxicity and ability to support stem cell differentiation in vitro. The hydrogels examined were pluronic F127 (PF127), Matrigel and PuraMatrix. We found that PF127, in a gelated (30%) form, was toxic to hNSCs, and Matrigel, in a gelated (1-50%) form, prevented hNSCs' normal capacity for neuronal differentiation. In contrast, PuraMatrix was the most optimal hydrogel for hNSCs, since it showed low toxicity when gelated (0.25%) and retained several crucial properties of hNSCs, including migration and neuronal differentiation. Further optimization and characterization of PuraMatrix is warranted to explore its full potential in assisting neural regeneration in vivo.

Thermally-induced glass formation from hydrogel nanoparticles

Amphiphilic hydrogel nanoparticles, composed of covalently cross-linked Pluronic F127 and PEG, exhibit a temperature- and concentration-dependent gelation in water which is interpreted as a colloidal glass formation. The possible applications of these phenomena in biomaterials and controlled release are also discussed.

A review of poloxamer 407 pharmaceutical and pharmacological characteristics

Poloxamer 407 copolymer (ethylene oxide and propylene oxide blocks) shows thermoreversible properties, which is of the utmost interest in optimising drug formulation (fluid state at room temperature facilitating administration and gel state above sol-gel transition temperature at body temperature promoting prolonged release of pharmacological agents). Pharmaceutical evaluation consists in determining the rheological behaviour (flow curve or oscillatory studies), sol-gel transition temperature, in vitro drug release using either synthetic or physiological membrane and (bio)adhesion characteristics. Poloxamer 407 formulations led to enhanced solubilisation of poorly water-soluble drugs and prolonged release profile for many galenic applications (e.g., oral, rectal, topical, ophthalmic, nasal and injectable preparations) but did not clearly show any relevant advantages when used alone. Combination with other excipients like Poloxamer 188 or mucoadhesive polymers promotes Poloxamer 407 action by optimising sol-gel transition temperature or increasing bioadhesive properties. Inclusion of liposomes or micro(nano)particles in Poloxamer 407 formulations offers interesting prospects, as well. Besides these promising data, Poloxamer 407 has been held responsible for lipidic profile alteration and possible renal toxicity, which compromises its development for parenteral applications. In addition, new findings have demonstrated immuno-modulation and cytotoxicity-promoting properties of Poloxamer 407 revealing significant pharmacological interest and, hence, human trials are in progress to specify these potential applications.

Mucoadhesive, thermosensitive, prolonged-release vaginal gel for clotrimazole:beta-cyclodextrin complex

The purpose of this study was to achieve a better therapeutic efficacy and patient compliance in the treatment for vaginitis. Clotrimazole (1%) has been formulated in a vaginal gel using the thermosensitive polymer Pluronic F127 (20%) together with mucoadhesive polymers such as Carbopol 934 and hydroxypropylmethylcellulose (0.2% for both). To increase its aqueous solubility, clotrimazole was incorporated as its inclusion complex with 1:1 molar ratio with beta-cyclodextrin. The inclusion complex was thoroughly characterized using various techniques, including 1H NMR spectroscopy, FT IR spectrophotometry, differential scanning calorimetry, scanning electron microscopy, phase solubility studies, and determination of stability constant (k(1:1)). The gelation temperature and rheological behavior of different formulations at varying temperatures were measured. In vitro release profiles of the gels were determined in pH 5.5 citrate buffer. It was observed that complexation with cyclodextrin slowed down the release of clotrimazole considerably. Carbopol 934, on the other hand, was found to interact with beta-cyclodextrin, inducing precipitation. As far as rheological properties are concerned, thermosensitive in situ gelling was obtained with formulations containing drug:cyclodextrin complex rather than with free drug. Thus, the optimum formulation for a controlled-release thermosensitive and mucoadhesive vaginal gel was determined to be clotrimazole:beta-cyclodextrin 1% with 0.2% hydroxypropylmethylcellulose in Pluronic F127 gel (20%) providing continuous and prolonged release of active material above MIC values.

Catanionic mixtures involving a drug: A rather general concept that can be utilized for prolonged drug release from gels

The aim of this work was to study at what extent mixtures of drug substances and oppositely charged surfactants form catanionic aggregates and to apply these as a means of obtaining prolonged drug release from a gel. The properties of traditional catanionic mixtures are relatively well known, but only recently we found that not only traditional surfactants form these mixtures, but also structurally more complex surface active drug compounds. In this study, several different compositions of catanionic mixtures were studied visually, by cryogenic transmission electron microscopy (cryo-TEM) and rheologically using a Bohlin VOR Rheometer. Some of the catanionic vesicle and micelle phases were incorporated in and released from gels using the USP paddle method. The drug compounds investigated were lidocaine, ibuprofen, naproxen, alprenolol, propranolol, and orphenadrine. Of the six drug molecules used in this study, five, both positively and negatively charged, were capable of forming catanionic vesicles and/or micelles with oppositely charged surfactants. The drug release studies show that catanionic drug surfactant mixtures are beneficial for obtaining prolonged release from gels, as the drug release using catanionic vesicles and micelles was prolonged between 10 and 100 times compared to the release of pure drug substance from the gel.

Three-Dimensional BioAssembly Tool for Generating Viable Tissue-Engineered Constructs

The primary emphasis of tissue engineering is the design and fabrication of constructs for the replacement of nonfunctional tissue. Because tissue represents a highly organized interplay of cells and extracellular matrix, the fabrication of replacement tissue should mimic this spatial organization. This report details studies evaluating the use of a three-dimensional, direct-write cell deposition system to construct spatially organized viable structures. A direct-write bioassembly system was designed and fabricated to permit layer-by-layer placement of cells and extracellular matrix on a variety of material substrates. Human fibroblasts suspended in polyoxyethylene/polyoxypropylene were coextruded through a positive displacement pen delivery onto a polystyrene slide. After deposition, approximately 60% of the fibroblasts remained viable. Bovine aortic endothelial cells (BAECs) suspended in soluble collagen type I were coextruded via microdispense pen delivery onto the hydrophilic side of flat sheets of polyethylene terephthalate. After deposition with a 25-gauge tip, approximately 86% of the BAECs were viable. When maintained in culture for up to 35 days, the constructs remained viable and maintained their original spatial organization. These results indicate the potential for utilizing a direct-write, three-dimensional bioassembly tool to create viable, patterned tissue-engineered constructs.

Ocular tolerability of Eudragit RS100 and RL100 nanosuspensions as carriers for ophthalmic controlled drug delivery

Polymeric nanoparticle suspensions were prepared from inert polymer resins (Eudragit RS100, RS, and RL100, RL). When loaded with drugs, these resins have been recently proposed as delivery systems to prolong the release and improve ocular availability of the drug. To verify the absence of toxicity toward the ocular structures, blank RS and RL nanosuspensions were applied to rabbit eye and a modified Draize test was performed. Polymer nanoparticles appeared to be avoiding of any irritant effect on cornea, iris, and conjunctiva up to 24 h after application, thus appearing to be a suitable inert carrier for ophthalmic drug delivery.

Evaluation of drug release from gels on pig nasal mucosa in a horizontal Ussing chamber

In this study, controlled release gel formulations containing dihydroalprenolol (DHA), hydrocortisone (HC) or testosterone (TS) in Carbopol 934P (C934) were evaluated using pig nasal mucosa in a horizontal Ussing chamber. The controlled release gel formulations were designed by including DHA in vesicle bilayers formed with sodium dodecyl sulphate (SDS) (1.4 and 36 mM) and by partitioning TS to the core of Brij 58 (B58, 1%) micelles. For comparison, unmodified gels and solutions of the drugs and additives were examined in parallel experiments. The viability and toxicity were evaluated with electrophysiological measurements and light microscopy. The results showed that C934 did not affect the viability of the mucosa and that the rate and profile of the appearance on the receiver side was independent of whether the substances were released from an unmodified gel or an unmodified solution. Continuous electrophysiological measurements made during exposure showed that B58 (1%) and SDS (1.4 mM) inactivated the mucosa, whereas SDS (36 mM) activated it. Investigations made after a 90-min exposure to the formulations showed that all the modified gels had inactivated the mucosa and had negative effects on the morphology. For the TS-B58 (1%) and the DHA-SDS (36 mM) gels, the rate-limiting step in transport was the release from the formulation. The results confirmed that gels from C934 are suitable for nasal administration and also clearly indicated the different degrees of toxicity of the controlled release formulations evaluated in this study. The horizontal Ussing chamber method was a suitable tool for the evaluation of gels for nasal administration.

Rheological evaluation of thermosensitive and mucoadhesive vaginal gels in physiological conditions

The timely gelation and retention of in situ-gelling vaginal formulations would be fundamental to improve the efficacy of drugs. In this study, various rheological properties of clotrimazole gels were evaluated for predicting their performance in vagina. Two kinds of thermosensitive and mucoadhesive formulations were composed of poloxamer 407 (P407, 15%), polycarbophil (0.2%), and different amounts of P188 (15 vs. 20%). Both formulations were Newtonian at 20 degrees C but non-Newtonian at 37 degrees C. Although both liquid formulations gelled below the vaginal temperature, they differed in gelation time and viscoelastic properties in the presence of vaginal fluid simulant. At body temperature, the formulation with 20% of P188 gelled within 35 s but it took two times longer for the other one gelled. Upon dilution with simulated vaginal fluid, the formulation with 20% of P188 retained the rheology of a gel, but the other one lost the viscoelastic properties typical for a gel. Moreover, after dilution with simulated vaginal fluid, the elastic modulus was orders of magnitude higher in the formulations with 20% of P188 relative to the other one. These results indicate that the rheological evaluation at the physiologic conditions needs to be preceded to develop more effective in situ-gelling vaginal formulations.

Controlled Drug Release from Gels Using Lipophilic Interactions of Charged Substances with Surfactants and Polymers

The aim of this article was to study interactions between different gel forming polymers and amphiphilic drugs and surfactants with the intention of finding interactions that can be used for designing controlled release formulations. The release from gels was measured by detecting the UV-absorbance of drugs released from 6 mL gel into 250 mL release medium in a dissolution bath. The rheological behavior of gels was characterized using a controlled rate rheometer. The diffusion coefficient of alprenolol was 6.3 x 10(-6) cm(2)/s when formulated in a 1% poly(acrylic acid) gel (PAA) and 2.8 x 10(-6) cm(2)/s in a lipophilically modified gel (LM-PAA). The addition of alprenolol to 1% LM-PAA increased the elasticity, G', from 123 to 182 Pa. Increased gel strength was also observed for a number of other amphiphilic drugs. The addition of 1% Brij 58 to LM-PAA decreased the diffusion coefficient of alprenolol to 2.3 x 10(-6) cm(2)/s. It was possible to sustain the release of charged drugs with high log P by adding surfactant micelles. However, the effect was small and only useful for drugs with adequate lipophilicity. The interaction between LM-PAA and amphiphilic drugs could be seen using rheology and was used for designing controlled release gel formulations. In this way surfactants can be avoided, thus decreasing toxicity problems.

Controlled drug release from gels using surfactant aggregates. II. Vesicles formed from mixtures of amphiphilic drugs and oppositely charged surfactants

PURPOSE

The aim of this study was to control the release of charged drugs from gels by adding surfactants that can interact with the drug and polymer matrix.

METHODS

The in vitro release from gels was measured by using 6-mL gel holders immersed in 250 mL of simulated tear fluid and detecting the ultraviolet absorbance on-line. Gels were characterized by using a controlled rate rheometer, and surfactant aggregates were characterized by using cryo-transmission electron microscopy.

RESULTS

The diffusion coefficient of alprenolol was 2.8 x 10(-6) cm2/s in a lipophilically modified poly(acrylic acid) gel without surfactants present and 0.14 x 10(-6) cm2/s when formulated with 1% sodium dodecyl sulfate. For fluvastatin, the diffusion coefficient changed from 3.0 x 10(-6) cm2/s to 0.07 x 10(-6) cm2/s in the presence of 0.2% benzyldimethyldodecyl-ammonium bromide. Alprenolol, betaxolol, metoprolol, diphenhydramine, and fluvastatin formed vesicles with oppositely charged surfactants in physiologic salt conditions.

CONCLUSIONS

In this article we show that it is feasible to control the release of charged drugs from gels by using surfactants. Vesicles are generally formed when surface active drugs are mixed with oppositely charged surfactants in physiologic conditions. The strongest effects on the release rate are seen for lipophilically modified polymer gels in which the drug and the oppositely charged surfactant form vesicles, but systems with micelles also give a slower release.