Model-Informed Drug Development: In Silico Assessment of Drug Bioperformance following Oral and Percutaneous Administration.

The pharmaceutical industry has faced significant changes in recent years, primarily influenced by regulatory standards, market competition, and the need to accelerate drug development. Model-informed drug development (MIDD) leverages quantitative computational models to facilitate decision-making processes. This approach sheds light on the complex interplay between the influence of a drug's performance and the resulting clinical outcomes. This comprehensive review aims to explain the mechanisms that control the dissolution and/or release of drugs and their subsequent permeation through biological membranes. Furthermore, the importance of simulating these processes through a variety of in silico models is emphasized. Advanced compartmental absorption models provide an analytical framework to understand the kinetics of transit, dissolution, and absorption associated with orally administered drugs. In contrast, for topical and transdermal drug delivery systems, the prediction of drug permeation is predominantly based on quantitative structure-permeation relationships and molecular dynamics simulations. This review describes a variety of modeling strategies, ranging from mechanistic to empirical equations, and highlights the growing importance of state-of-the-art tools such as artificial intelligence, as well as advanced imaging and spectroscopic techniques.

Evaluation of chitosan/xanthan gum polyelectrolyte complexes potential for pH-dependent oral delivery of escin.

Escin is an amphiphilic and weakly acidic drug that oral administration may lead to the irritation of gastric mucosa. The entrapment of escin into chitosan (CH)/xanthan gum (XG)-based polyelectrolyte complexes (PECs) can facilitate controlled drug release which may be beneficial for the reduction of its side effects. This study aimed to investigate the influence of escin content and drying method on the formation, physicochemical, and controlled, pH-dependent drug release properties of CH/XG-based PECs. Measurements of transmittance, conductivity, and rheological characterization confirmed the formation of CH/XG-based PECs with escin entrapped at escin-to-polymers mass ratios 1:1, 1:2, and 1:4. Ambient-dried PECs had higher yield, entrapment efficiency, and escin content in comparison with spray-dried ones. FT-IR spectra confirmed the interactions between CH, XG, and escin, which were stronger in ambient-dried PECs. PXRD and DSC analyses showed the amorphous escin character in all dry PECs, regardless of the drying method. The most promising controlled and pH-dependent in vitro escin release was from the ambient-dried PEC at the escin-to-polymers mass ratio of 1:1. For that reason and due to the highest yield and entrapment efficiency, this carrier has the potential to prevent the irritation of gastric mucosa after oral administration of escin.

Percutaneous delivery of levetiracetam as an alternative to topical nonsteroidal anti-inflammatory drugs: formulation development, in vitro and in vivo characterization.

The study focused on formulation of carmellose sodium hydrogels and nonionic microemulsions with 5% and 10% of levetiracetam and investigation of drug concentration influence on their physicochemical characteristics and in-use stability as well as influence of drug concentration and carrier type on in vitro drug release and in vivo antihyperalgesic/antiedematous activity in a rat model of localized (intraplantar) carrageenan-induced inflammation. Hydrogels were pseudoplastic semisolids with thixotropy and pH 7.37-7.58. Microemulsions were low viscous Newtonian nanodispersions of oil droplets (13.11-15.11 nm) in water, with pH 4.01-4.64. Physical stability of the investigated systems was preserved over the 3-month storage under ambient conditions. Levetiracetam release followed zero order and Korsmeyer-Peppas models (R2 ≥ 0.99) reflecting the combined effects of drug concentration and carrier viscosity. All levetiracetam-loaded formulations produced significant reduction of hyperalgesia and paw swelling induced by carrageenan (p < 0.001). Their efficacy in exerting antihyperalgesic activity was significantly higher than that observed with the reference 5% ibuprofen hydrogel preparation (up to 6 h) (p < 0.001), while antiedematous activity was comparable with the reference product. No erythema and visible blood vessels were observed in a rat ear test. The study demonstrated percutaneous delivery of levetiracetam as useful and safe therapeutic option for localized inflammatory pain with potential to overcome the insufficient efficacy of topically applied nonsteroidal anti-inflammatory drugs in the form of a hydrogel. Graphical abstract.

Effect of ibuprofen entrapment procedure on physicochemical and controlled drug release performances of chitosan/xanthan gum polyelectrolyte complexes.

The effect of the entrapment procedure of a poorly water soluble drug (ibuprofen) on physicochemical and drug release performances of chitosan/xanthan polyelectrolyte complexes (PECs) was investigated to achieve controlled drug release as the ultimate goal. The formation of PECs for two drug entrapment procedures (before or after the mixing of polymers) at pH 4.6 and 5.6 and three chitosan-to-xanthan mass ratios (1:1, 1:2 and 1:3) was observed by continuous decrease in conductivity during the PECs formation and increased apparent viscosity and hysteresis values. The most extensive crosslinking was observed with ibuprofen added before the PECs formation at pH 4.6 and chitosan-to-xanthan mass ratio 1:1. The PECs prepared at polymers' mass ratios 1:2 and 1:3 had higher yield and drug entrapment efficiency. DSC and FT-IR analysis confirmed ibuprofen entrapment in PECs and the partial disruption of its crystallinity. All ibuprofen release profiles were similar, with 60-70% of drug released after 12 h, mainly by diffusion, but erosion and polymer chain relaxation were also included. Potentially optimal can be considered the PEC prepared at pH 4.6, ibuprofen entrapped before the mixing of polymers at chitosan-to-xanthan mass ratio 1:2, which provided controlled drug release by zero-order kinetics, high yield, and drug entrapment efficiency.

Study of chitosan/xanthan gum polyelectrolyte complexes formation, solid state and influence on ibuprofen release kinetics.

This study investigated the combined influence of pH adjusting agent type (hydrochloric, acetic or lactic acid) and initial pH value (3.6, 4.6, and 5.6) on formation of biocompatible chitosan/xanthan polyelectrolyte complexes (PECs), their characteristics in solid state and influence on in vitro ibuprofen release kinetics. Conductivity measurements and rheological characterization revealed generally higher extent of ionic interactions in PEC dispersions comprising acetic acid and at pH 3.6. Acid type and pH affected significantly the yield and particle size (100-250 µm) of the dried PECs. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and powder X-ray diffraction (PXRD) analysis of the solid PECs confirmed exclusively physical (ionic, hydrogen bonds) interactions between chitosan and xanthan gum. PECs prepared with acetic acid at pH 4.6 and 5.6 had enhanced rehydration ability in phosphate buffer pH 7.2, and at PEC-to-drug mass ratio up to 1:2, enabled extended ibuprofen release from hard capsules during 10 h.

Composite chitosan hydrogels as advanced wound dressings with sustained ibuprofen release and suitable application characteristics.

The physical chitosan hydrogel, obtained by ionic gelation in lactic acid solution, was combined with biocompatible oil-in-water microemulsion with ibuprofen, to prepare composite hydrogels with 0.25-1% of the polymer and 5% of the drug. The electrical conductivity measurement, photon correlation spectroscopy (PCS), and rheological analysis showed that the composite hydrogels comprise oil nanodroplets (16.21-22.56 nm) embedded within pseudoplastic chitosan hydrogel. In vitro ibuprofen release was sustained for 12 h and followed zero-order kinetics. pH values of the composite hydrogels were in the range of 4.80-5.27, thus physiologically acceptable. The formulation containing 0.5% chitosan enabled the maximum drug release rate of 239.25 µgh-1cm-2 as well as cohesiveness (154.958 ± 0.731 g*s) higher than hardness (13.546 ± 0.065 g) and adhesiveness (-12.042 ± 1.161 g*s), so textural properties were suitable for application along skin surface, without spillage, and for easy removal. This is the first study in which the composite chitosan hydrogels with ibuprofen were formulated by combining the chitosan hydrogel prepared without harmful chemical crosslinkers and low viscosity oil-in-water microemulsion, and the preclinical characterization of their biopharmaceutical aspect and textural characterization, that is of key importance in improving the patient's compliance, were performed.

Topical hydrogels with escin ß-sitosterol phytosome and escin: Formulation development and in vivo assessment of antihyperalgesic activity.

The physicochemical properties, stability, in vivo antihyperalgesic activity, and skin irritation potential of the carbomer hydrogels with the new chemical entity escin ß-sitosterol (ES) phytosome were characterized and compared with those containing escin. Physicochemical characterization of the hydrogels (performed 48 hr after preparation) included organoleptic examination, pH measurement, light microscopy, differential scanning calorimetry analysis and rheological tests. The obtained results showed that increasing concentration of the active substances within 1-5% affected the appearance (color and transparency) of the hydrogels, their pH, consistency, and rheological behavior. Unlike acidic escin, which was dissolved in the liquid phase of the pseudoplastic hydrogels E1-E5 and reduced their maximal apparent viscosity (ηmax ), minimal apparent viscosity (ηmin ), and hysteresis area (H) in comparison to the plain carbomer hydrogel, amphiphilic ES-enhanced ηmax , ηmin , and thixotropy of the hydrogels ES1-ES5, which is favorable for prolonged retention at skin surface. Evaluation of in-use stability of the hydrogels showed that organoleptic characteristics, flow behavior, and pH values could be preserved for 3 months under ambient conditions. The rat ear test results suggested that the hydrogels are safe to be used on human skin. Both escin and ES-loaded hydrogels exerted significant, concentration-dependent antihyperalgesic effect in inflammatory pain model in rats. ES-loaded hydrogels were significantly more effective than those loaded with escin. This is a first report on the antihyperalgesic effect of topically applied escin as well as ES in a model of inflammatory pain.

Comparison of the Effect of Bioadhesive Polymers on Stability and Drug Release Kinetics of Biocompatible Hydrogels for Topical Application of Ibuprofen.

The study is focused on formulation of biocompatible hydrogels with a poorly soluble drug ibuprofen (5%) and comprehensive evaluation and comparison of effect of different bioadhesive polymers on their suitability for application on skin, physical stability during the accelerated and natural aging tests (by performing centrifugation test, light microscopy, differential scanning calorimetry, rheological and pH measurements), and in vitro drug release kinetics. Hydrogels, formulated with xanthan gum 1% (XIB), sodium carboxymethylcellulose 5% (CMCIB), poloxamer 407 16% (PIB), and carbomer 1% (KIB), were soft pseudoplastic semisolids with thixotropy and biocompatible pH. The type of the polymer significantly affected apparent viscosity of the hydrogels and miscibility rate with artificial sweat, their physical stability, and shape, size, and aggregation of the drug crystals and degree of crystallization. The drug release in all investigated hydrogels was diffusion-controlled in accordance with the Higuchi model and sustained for 12 h, with the drug release rate and the amount of drug released depended on the polymer. The described formulation approach enabled discrimination of the hydrogels with unsatisfactory application properties (CMCIB) and physical stability (KIB), and selection of the hydrogel with promising characteristics in terms of all investigated aspects (XIB) which could be considered for further evaluation.

Semisolid self-microemulsifying drug delivery systems (SMEDDSs): Effects on pharmacokinetics of acyclovir in rats.

Semisolid self-microemulsifying drug delivery system (SMEDDS) with optimized drug loading capacity, stability, dispersibility in aqueous media and in vitro drug release profile, was evaluated in vivo regarding effects on pharmacokinetics of acyclovir, an antiviral with low bioavailability (BA) and short half-life (t1/2). Additional goal of this study was evaluation of safety of this semisolid SMEDDS consisted of medium chain length triglycerides (oil) (10% w/w), macrogolglycerol hydroxystearate (surfactant) (56.25% w/w), polyglyceryl-3-dioleate (cosurfactant) (6.25% w/w), glycerol (cosolvent) (20% w/w), macrogol 8000 (viscosity modifier) (7.5% w/w), and acyclovir (2.5 mg/ml). The study was performed on fully mature white male Wistar rats. The pharmacokinetics of acyclovir was monitored in three groups (1-3) of animals after administration of drug solution (intravenously (IV)), drug suspension (orally) and semisolid SMEDDS (orally), respectively. The determined pharmacokinetic parameters were: maximum concentration of acyclovir in serum (Cmax), time taken to reach Cmax (Tmax), areas under time-concentration curves (AUC0-t and AUC0-∞), terminal elimination rate constant (kel), t1/2, volume of distribution (Vd), mean residence time (MRT), clearance (Cl), zero concentration (C0), steady state volume of distribution (Vss), and BA. Additionally, for safety evaluation, animals were treated orally with aqueous solution of acyclovir, drug-free semisolid SMEDDS and acyclovir-loaded semisolid SMEDDS, during 21 days (groups 4-7). Serum samples of sacrificed animals were used for biochemical analysis of enzymatic activity of alanine transaminase (ALT) and aspartate transaminase (AST), urea, creatinine, and uric acid. Acyclovir administered by semisolid SMEDDS reached twice higher Cmax (0.92 ±â€¯0.21 µg/ml) and has significantly shorter Tmax (14 ±â€¯10.84 min) compared to the suspension of acyclovir (Cmax 0.29 ±â€¯0.09 µg/ml and Tmax 26.00 ±â€¯5.48 min). BA of the drug was significantly increased by semisolid SMEDDS, while the analysis of biochemical parameters excluded damage on function of liver and kidneys caused by the investigated drug delivery system.

Development of semisolid self-microemulsifying drug delivery systems (SMEDDSs) filled in hard capsules for oral delivery of aciclovir.

The study aimed to develop semisolid self-microemulsifying drug delivery systems (SMEDDSs) as carriers for oral delivery of aciclovir in hard hydroxypropylmethyl cellulose (HPMC) capsules. Six self-dispersing systems (SD1-SD6) were prepared by loading aciclovir into the semisolid formulations consisting of medium chain length triglycerides (lipid), macrogolglycerol hydroxystearate (surfactant), polyglyceryl-3-dioleate (cosurfactant), glycerol (hydrophilic cosolvent), and macrogol 8000 (viscosity modifier). Their characterization was performed in order to identify the semisolid system with rheological behaviour suitable for filling in hard HPMC capsules and fast dispersibility in acidic and alkaline aqueous media with formation of oil-in-water microemulsions. The optimal SMEDDS was loaded with aciclovir at two levels (2% and 33.33%) and morphology and aqueous dispersibility of the obtained systems were examined by applying light microscopy and photon correlation spectroscopy (PCS), respectively. The assessment of diffusivity of aciclovir from the SMEDDSs by using an enhancer cell model, showed that it was increased at a higher drug loading. Differential scanning calorimetry (DSC) analysis indicated that the SMEDDSs were semisolids at temperatures up to 50°C and physically stable and compatible with HPMC capsules for 3 months storage at 25°C and 4°C. The results of in vitro release study revealed that the designed solid dosage form based on the semisolid SMEDDS loaded with the therapeutic dose of 200mg, may control partitioning of the solubilized drug from in situ formed oil-in-water microemulsion carrier into the sorrounding aqueous media, and hence decrease the risk for precipitation of the drug.

Formulation of hydrogel-thickened nonionic microemulsions with enhanced percutaneous delivery of ibuprofen assessed in vivo in rats.

The study investigated usage of hydrogel of an anionic polymer xanthan gum for design of ibuprofen-loaded hydrogel-thickened microemulsions (HTMs) from the nonionic oil-in-water microemulsion (M). Xanthan gum demonstrated the performances of a thickening agent in physically stable HTMs at 5±3°C, 20±3°C, and 40±1°C during 6months. The results of physicochemical characterization (pH, conductivity, rheological behaviour, spreadability) indicated that HTMs containing 0.25-1.00% of the polymer had colloidal structure with oil nanodroplets of 14.34±0.98nm (PdI 0.220±0.075) dispersed in aqueous phase thickened with the polymer gel network which strength depended on the polymer concentration. HTMs with ibuprofen (5%) were evaluated as percutaneous drug delivery carriers. In vitro ibuprofen release from HTMs followed zero order kinetic (r>0.995) for 12h, while the referent hydrogel was described by Higuchi model. The HTM with optimized drug release rate and spreadability (HTM1) and the polymer-free microemulsion (M) were assessed and compared with the referent hydrogel in in vivo studies in rats. HTM1 and M were significantly more efficacious than reference hydrogel in producing antihyperalgesic and at lower extent antiedematous activity in prophylactic topical treatment protocol, whilst they were comparable in producing antihyperalgesic/antiedematous effects in therapeutic protocol. Topical treatments produced no obvious skin irritation.

Evaluation of critical formulation parameters in design and differentiation of self-microemulsifying drug delivery systems (SMEDDSs) for oral delivery of aciclovir.

The study investigated the influence of formulation parameters for design of self-microemulsifying drug delivery systems (SMEDDSs) comprising oil (medium chain triglycerides) (10%), surfactant (Labrasol(®), polysorbate 20, or Kolliphor(®) RH40), cosurfactant (Plurol(®) Oleique CC 497) (q.s. ad 100%), and cosolvent (glycerol or macrogol 400) (20% or 30%), and evaluate their potential as carriers for oral delivery of a poorly permeable antivirotic aciclovir (acyclovir). The drug loading capacity of the prepared formulations ranged from 0.18-31.66 mg/ml. Among a total of 60 formulations, three formulations meet the limits for average droplet size (Z-ave) and polydispersity index (PdI) that have been set for SMEDDSs (Z-ave≤100nm, PdI<0.250) upon spontaneous dispersion in 0.1M HCl and phosphate buffer pH 7.2. SMEDDSs with the highest aciclovir loading capacity (24.06 mg/ml and 21.12 mg/ml) provided the in vitro drug release rates of 0.325 mg cm(-2)min(-1) and 0.323 mg cm(-2)min(-1), respectively, and significantly enhanced drug permeability in the parallel artificial membrane permeability assay (PAMPA), in comparison with the pure drug substance. The results revealed that development of SMEDDSs with enhanced drug loading capacity and oral delivery potential, required optimization of hydrophilic ingredients, in terms of size of hydrophilic moiety of the surfactant, surfactant-to-cosurfactant mass ratio (Km), and log P of the cosolvent.

Design of Block Copolymer Costabilized Nonionic Microemulsions and Their In Vitro and In Vivo Assessment as Carriers for Sustained Regional Delivery of Ibuprofen via Topical Administration.

Nonionic surfactants (caprylocaproyl macrogol-8 glycerides, octoxynol-12, polysorbate-20, and polyethylene glycol-40 hydrogenated castor oil) (47.03%, w/w), costabilizer (poloxamer 407) (12%-20%, w/w), oil (isopropyl myristate) (5.22%, w/w), water (q.s. ad 100%, w/w), and ibuprofen (5%, w/w) were used to develop oil-in-water microemulsions with Newtonian flow behavior, low viscosity (from 368 ± 38 to 916 ± 46 mPa s), and average droplet size from 14.79 ± 0.31 to 16.54 ± 0.75 nm. Ibuprofen in vitro release from the microemulsions was in accordance with zero-order kinetics (R0(2) > 0.99) for at least 12 h. The maximum drug release rate (3.55%h(-1) ) was from the microemulsion M3 comprising 16%, w/w of poloxamer 407. The release rate of ibuprofen from the reference hydrogel followed Higuchi kinetics (RH(2) > 0.99), and drug amount released after the 6th hour was negligible. In a rat model of inflammation, the microemulsion M3 was significantly more efficacious than the reference hydrogel in exerting antihyperalgesic effects in prophylactic topical treatment, whereas they were comparable in therapeutic treatment as well as in producing antiedematous effect in both protocols. No obvious skin irritation was observed in in vivo studies. The developed nonionic surfactants-based microemulsions containing the optimal concentration of poloxamer 407 could be promising carriers for sustained regional delivery of ibuprofen via topical administration.

Characterization of gelation process and drug release profile of thermosensitive liquid lecithin/poloxamer 407 based gels as carriers for percutaneous delivery of ibuprofen.

Suitability of liquid lecithin (i.e., solution of lecithin in soy bean oil with ∼ 60% w/w of phospholipids) for formation of gels, upon addition of water solution of poloxamer 407, was investigated, and formulated systems were evaluated as carriers for percutaneous delivery of ibuprofen. Formulation study of pseudo-ternary system liquid lecithin/poloxamer 407/water at constant liquid lecithin/poloxamer 407 mass ratio (2.0) revealed that minimum concentrations of liquid lecithin and poloxamer 407 required for formation of gel like systems were 15.75% w/w and 13.13% w/w, respectively, while the maximum content of water was 60.62% w/w. The systems comprising water concentrations in a range from 55 to 60.62% w/w were soft semisolids suitable for topical application, and they were selected for physicochemical and biopharmaceutical evaluation. Analysis of conductivity results and light microscopy examination revealed that investigated systems were water dilutable dispersions of spherical oligolamellar associates of phospholipids and triglyceride molecules in the copolymer water solution. Rheological behavior evaluation results indicated that the investigated gels were thermosensitive shear thinning systems. Ibuprofen (5% w/w) was incorporated by dispersing into the previously prepared carriers. Drug-loaded systems were physically stable at storage temperature from 5 ± 3°C to 40 ± 2°C, for 30 days. In vitro ibuprofen release was in accordance with the Higuchi model (rH>0.95) and sustained for 12h. The obtained results implicated that formulated LLPBGs, optimized regarding drug release and organoleptic properties, represent promising carriers for sustained percutaneous drug delivery of poorly soluble drugs.

Characterization and evaluation of solid self-microemulsifying drug delivery systems with porous carriers as systems for improved carbamazepine release.

The purpose of this study was to investigate solid self-microemulsifying drug delivery system (SSMEDDS), as potential delivery system for poorly water soluble drug carbamazepine (CBZ). Self-microemulsifying drug delivery system (SMEDDS) was formulated using the surfactant polyoxyethylene 20 sorbitan monooleate [Polysorbate 80] (S), the cosurfactant PEG-40 hydrogenated castor oil [Cremophor(®) RH40] (C) and the oil caprylic/capric triglycerides [Mygliol(®) 812] (O). Four different adsorbents with high specific surface area were used: Neusilin(®) UFL2, Neusilin(®) FL2 (magnesium aluminometasilicate), Sylysia(®) 320 and Sylysia(®) 350 (porous silica). Microemulsion area at the surfactant to cosurfactant ratio (K(m)) 1:1 was evaluated and for further investigation SMEDDS with SC/O ratio 8:2 was selected. Solubilization capacity of selected SMEDDS for CBZ was 33.771±0.041 mg/ml. Rheological measurements of unloaded and CBZ-loaded SMEDDS at water content varied from 10 to 60% (w/w) were conducted. It has been found that CBZ has great influence on rheological behaviour of investigated system upon water dilution. Photon correlation spectroscopy has shown the ability of CBZ-loaded SMEDDS to produce microemulsion droplet size. SSMEDDS improved release rate of CBZ, but the type of adsorbent significantly affects release rate of CBZ. For SSMEDDS with different magnesium aluminometasilicate adsorbents, release rate of CBZ decreased with increasing specific surface area due to entrapment of liquid SMEDDS inside the pores and its gradual exposure to dissolution medium. With porous silica adsorbents no difference in release rate was found in comparison to physical mixtures. In physical mixtures at 12.5% (w/w) CBZ content, presence of amorphous CBZ led to high dissolution rate.

Investigation of surfactant/cosurfactant synergism impact on ibuprofen solubilization capacity and drug release characteristics of nonionic microemulsions.

The current study investigates the performances of the multicomponent mixtures of nonionic surfactants regarding the microemulsion stabilisation, drug solubilization and in vitro drug release kinetic. The primary surfactant was PEG-8 caprylic/capric glycerides (Labrasol). The cosurfactants were commercially available mixtures of octoxynol-12 and polysorbate 20 without or with the addition of PEG-40 hydrogenated castor oil (Solubilisant gamma 2421 and Solubilisant gamma 2429, respectively). The oil phase of microemulsions was isopropyl myristate. Phase behaviour study of the pseudo-ternary systems Labrasol/cosurfactant/oil/water at surfactant-to-cosurfactant weight ratios (K(m)) 40:60, 50:50 and 60:40, revealed a strong synergism in the investigated tensides mixtures for stabilisation of microemulsions containing up to 80% (w/w) of water phase at surfactant +cosurfactant-to-oil weight ratio (SCoS/O) 90:10. Solubilization of a model drug ibuprofen in concentration common for topical application (5%, w/w) was achieved at the water contents below 50% (w/w). Drug free and ibuprofen-loaded microemulsions M1-M6, containing 45% (w/w) of water phase, were prepared and characterized by polarized light microscopy, conductivity, pH, rheological and droplet size measurements. In vitro ibuprofen release kinetics from the microemulsions was investigated using paddle-over-enhancer cell method and compared with the commercial 5% (w/w) ibuprofen hydrogel product (Deep Relief, Mentholatum Company Ltd., USA). The investigated microemulsions were isotropic, low viscous Bingham-type liquids with the pH value (4.70-6.61) suitable for topical application. The different efficiency of the tensides mixtures for microemulsion stabilisation was observed, depending on the cosurfactant type and K(m) value. Solubilisant gamma 2429 as well as higher K(m) (i.e., lower relative content of the cosurfactant) provided higher surfactant/cosurfactant synergism. The drug molecules were predominantly solubilized within the interface film. The amount of drug released from the formulations M3 (10.75%, w/w) and M6 (13.45%, w/w) (K(m) 60:40) was limited in comparison with the reference (22.22%, w/w) and follows the Higuchi model. Microemulsions M2 and M5 (K(m) 50:50) gave zero order drug release pattern and ∼15% (w/w) ibuprofen released. The release profiles from microemulsions M1 and M4 (K(m) 40:60) did not fit well with the models used for analysis, although the amounts of ibuprofen released (24.47%, w/w) and 17.99% (w/w), respectively) were comparable to that of the reference hydrogel. The drug release mechanism was related with the surfactant/cosurfactant synergism, thus the lower efficiency of the tensides corresponded to the faster drug release.

The application of artificial neural networks in the prediction of microemulsion phase boundaries in PEG-8 caprylic/capric glycerides based systems.

The objective of this study was to develop artificial neural network (ANN) model suitable to predict successfully the borders of the microemulsion region in the quaternary system PEG-8 caprylic/capric glycerides (Labrasol)/cosurfactant/isopropyl myristate/water, in order to minimise experimental effort. In our preliminary investigations of phase behaviour, two cosurfactants were used, PEG-40 hydrogenated castor oil (Cremophor) RH 40) and polyglyceryl-6 isostearate (Plurol Isostearique). Microemulsion existance area in pseudo-ternary phase diagrams was determined using titration method at constant: (a) oil-to-water ratio (alpha=50%, w/w); (b) surfactant-to-cosurfactant ratio (Km) 4:6; (c) Km 5:5; or (d) Km 6:4. It was found that the phase behaviour of systems involving polyoxyethylene type of cosurfactant depends significantly on oil-to-surfactant/cosurfactant mixture mass ratio (O/SCoS) but it is Km-independent. The formation of microemulsions in Labrasol/polyglyceryl-6 isostearate based systems was a complex function of Km and O/SCoS and there was employed a Generalized Regression Neural Network (GRNN) with four layers as a predictive mathematical model, using data obtained from the phase behaviour study (the surfactant concentration in surfactant/cosurfactant mixture (S, %, w/w), the oil concentration in the mixture with tensides (O, %, w/w) as two input variables, and the water solubilization limit (W(max), %, w/w) as output data). After network training, six independent pairs of input/output data were used for network testing. The resulting GRNN was tested statistically and found to be of quality predictive power. This results confirmed that the trained GRNN could be effective in predicting the size of the microemulsion area providing valuable tool in formulation of this type of colloidal vehicles.

The influence of cosurfactants and oils on the formation of pharmaceutical microemulsions based on PEG-8 caprylic/capric glycerides.

In the present study the effect of type and concentration of a cosurfactant and oil on the ability of nonionic surfactant PEG-8 caprylic/capric glycerides (Labrasol) to solubilize both oil and water phases was evaluated. Seven different cosurfactants (polyglyceryl-6 dioleate (Plurol Oleique) (PO), polyglyceryl-6 isostearate (Plurol Isostearique (PI), polyglyceryl-4 isostearate (Isolan GI 34) (IGI34), octoxynol-12 (and) polysorbate 20 (Solubilisant gamma) 2421) (SG2421), octoxynol-12 (and) polysorbate 20 (and) PEG-40 hydrogenated castor oil (Solubilisant gamma 2429) (SG2429), PEG-40 hydrogenated castor oil (Cremophor) RH 40) (CRH40) and diethyleneglycol monoethyl ether (Transcutol) and six oils (isopropyl myristate, ethyl oleate, decyl oleate, medium chain triglycerides, mineral oil and olive oil) were used in phase behaviour studies of a quaternary system Labrasol/cosurfactant/oil/water. The amount of surfactant required to completely homogenize equal masses of oil and water to form a single phase microemulsion (termed as balanced microemulsion) (S min, %w/w), the minimal concentration of the surfactant/cosurfactant blend required to produce a balanced microemulsion (SCoS min, %w/w) as well as the maximum concentration of water solubilized in investigated surfactant/oil and surfactant/cosurfactant/oil mixtures (W(max), %w/w) were determined. The obtained results indicated that Labrasol showed a good efficiency in the presence of lower molecular volume fatty acid esters with a preferred chemical structure such as isopropyl myristate (S min 56.14% (w/w); W(max) 12.28% (w/w)). Oils with high molecular volume (olive oil and mineral oil) do not result in microemulsion formation. Transcutol decreased the capacity of Labrasol for solubilization of oil and water phases. The tendency of Labrasol to solubilize both, water and oil phases, was favoured by polyglycerol-6 ester type of cosurfactants (PO and PI) while the influence of the polyglycerol-4 ester (IGI34) as well as of polyoxyethylene type of cosurfactants (CRH40, SG2421 and SG2429) on the surfactant efficiency, was not significant. Furthermore, the results revealed the significant influence of the surfactant/cosurfactant mass ratio (K(m)) on synergistic effect between polyglyceryl-6 esters and Labrasol in the formation of microemulsions using isopropyl myristate as oil phase. Optimized microemulsion systems were stabilized with Labrasol/polyglyceryl-6 esters blend at K(m) 5:5 (SCoS min, 27.5% (w/w) and W(max), 71.43% (w/w) for PI; SCoS min, 29.18% (w/w) and W(max), 65.00% (w/w) for PO) and the electrical conductivity measurement results for optimized balanced microemulsions showed that their structures were highly conductive indicating a bicontinuous microstructure.