Development of a Hydroxypropyl-β-Cyclodextrin-Based Liquid Formulation for the Oral Administration of Propranolol in Pediatric Therapy

Propranolol (PPN) is widely used in children to treat various cardiovascular diseases. The availability of a suitable PPN solution should avoid recourse to extemporaneous preparations of unknown/limited stability, as commonly made in hospital pharmacies. However, the development of pediatric PPN solutions is hindered by their instability to light and stability at pH ≈ 3, bitter taste, and the need to improve palatability and avoid co-solvents, flavoring agents, or preservatives that are potentially toxic. In this study, cyclodextrin (CD) complexation has been exploited to develop a safe, stable, and palatable oral pediatric solution of PPN. An initial screening among various CDs allowed us to select HPβCD for its good complexing ability and no toxicity. Drug-HPβCD physical mixtures or co-ground systems (1:1 or 1:2 mol:mol) were used to prepare 0.2% w/v drug solutions. Photo stability studies evidenced the protective effect of HPβCD, revealing a reduction of up to 75% in the drug degradation rate after 1 h of exposure to UV radiation. Storage stability studies showed unchanged physical-chemical properties and almost constant drug concentration after 6 months and under accelerated conditions (40 °C), despite the less aggressive pH (≈5.5) of the solution. The electronic tongue test proved that the HPβCD taste-masking properties improved the formulation palatability, with a 30% reduction in drug bitterness.

Design, Evaluation and Comparison of Nanostructured Lipid Carriers and Chitosan Nanoparticles as Carriers of Poorly Soluble Drugs to Develop Oral Liquid Formulations Suitable for Pediatric Use

There is a serious need of pediatric drug formulations, whose lack causes the frequent use of extemporaneous preparations obtained from adult dosage forms, with consequent safety and quality risks. Oral solutions are the best choice for pediatric patients, due to administration ease and dosage-adaptability, but their development is challenging, particularly for poorly soluble drugs. In this work, chitosan nanoparticles (CSNPs) and nanostructured lipid carriers (NLCs) were developed and evaluated as potential nanocarriers for preparing oral pediatric solutions of cefixime (poorly soluble model drug). The selected CSNPs and NLCs showed a size around 390 nm, Zeta-potential > 30 mV, and comparable entrapment efficiency (31-36%), but CSNPs had higher loading efficiency (5.2 vs. 1.4%). CSNPs maintained an almost unchanged size, homogeneity, and Zeta-potential during storage, while NLCs exhibited a marked progressive Zeta-potential decrease. Drug release from CSNPs formulations (differently from NLCs) was poorly affected by gastric pH variations, and gave rise to a more reproducible and controlled profile. This was related to their behavior in simulated gastric conditions, where CSNPs were stable, while NLCs suffered a rapid size increase, up to micrometric dimensions. Cytotoxicity studies confirmed CSNPs as the best nanocarrier, proving their complete biocompatibility, while NLCs formulations needed 1:1 dilution to obtain acceptable cell viability values.

Role of Cyclodextrins and Drug Solid State Properties on Flufenamic Acid Dissolution Performance from Tablets

Flufenamic acid (FFA) is a non-steroidal anti-inflammatory drug characterised by a low solubility and problems of variable dissolution rate and bio-inequivalence. Different FFA batches, obtained by different suppliers, showed different powder characteristics (particle size, shape and surface properties) that may affect its dissolution behaviour from solid dosage forms. Aim of this work was the improvement of FFA solubility and dissolution rate by the use of cyclodextrins (CDs) and the obtainment of an effective tablet formulation by direct compression. Several CDs have been tested, both in solution and in solid state and several binary systems drug-CDs have been obtained with different techniques, with the scope to select the most effective system. Grinding technique with randomly methylated-β-cyclodextrin (RAMEB) was the only one that allowed the complete drug amorphization, together with the highest improvement in drug dissolution rate, and was then selected for tablets formulation. Conventional and immediate release tablets were obtained and fully characterised for technological properties. In both cases an improved and well reproducible drug dissolution performance was obtained, independently from the FFA supplier and thus no more affected by the differences observed between the original FFA crystalline samples.

Combined Use of Cyclodextrins and Amino Acids for the Development of Cefixime Oral Solutions for Pediatric Use

Cefixime (CEF) is a cephalosporin included in the WHO Model List of Essential Medicines for Children. Liquid formulations are considered the best choice for pediatric use, due to their great ease of administration and dose-adaptability. Owing to its very low aqueous solubility and poor stability, CEF is only available as a powder for oral suspensions, which can lead to reduced compliance by children, due to its unpleasant texture and taste, and possible non-homogeneous dosage. The aim of this work was to develop an oral pediatric CEF solution endowed with good palatability, exploiting the solubilizing and taste-masking properties of cyclodextrins (CDs), joined to the use of amino acids as an auxiliary third component. Solubility studies indicated sulfobutylether-β-cyclodextrin (SBEβCD) and Histidine (His) as the most effective CD and amino acid, respectively, even though no synergistic effect on drug solubility improvement by their combined use was found. Molecular Dynamic and ¹H-NMR studies provided insight into the interactions of binary CEF:His and ternary CEF:His:SBEβCD systems used to prepare CEF solutions, which resulted stable and maintained unchanged antimicrobial activity during the two-weeks-use in therapy. The ternary solution was superior in terms of more tolerable pH (5.6 vs. 4.7) and better palatability, being resulted completely odorless by a panel test.

Development of a Cyclodextrin-Based Mucoadhesive-Thermosensitive In Situ Gel for Clonazepam Intranasal Delivery

A thermosensitive, mucoadhesive in-situ gel for clonazepam (CLZ) intranasal delivery was developed, which aimed to achieve prolonged in-situ residence and controlled drug release, overcoming problems associated with its oral or parenteral administration. Poloxamer was selected as a thermosensitive polymer and chitosan glutamate and sodium hyaluronate as mucoadhesive and permeation enhancer. Moreover, randomly methylated β-Cyclodextrin (RAMEB) was used to improve the low drug solubility. A screening DoE was applied for a systematic examination of the effect of varying the formulation components proportions on gelation temperature, gelation time and pH. Drug-loaded gels at different clonazepam-RAMEB concentrations were then prepared and characterized for gelation temperature, gelation time, gel strength, mucoadhesive strength, mucoadhesion time, and drug release properties. All formulations showed suitable gelation temperature (29-30.5 °C) and time (50-65 s), but the one with the highest drug-RAMEB concentration showed the best mucoadhesive strength, longest mucoadhesion time (6 h), and greatest release rate. Therefore, it was selected for cytotoxicity and permeation studies through Caco-2 cells, compared with an analogous formulation without RAMEB and a drug solution. Both gels were significantly more effective than the solution. However, RAMEB was essential not only to promote drug release, but also to reduce drug cytotoxicity and further improve its permeability.

Improvement of Butamben Anesthetic Efficacy by the Development of Deformable Liposomes Bearing the Drug as Cyclodextrin Complex

This work was aimed at enhancing butamben (BTB) anesthetic efficacy by the "drug-in cyclodextrin (CD)-in deformable liposomes" strategy. In the study, phase-solubility studies with natural (α-, β-, γ-) and derivative (hydroxypropyl-α-and β-, sulfobutylether-β, methyl-β) CDs evidenced the highest BTB affinity for βCD and its derivatives and indicated methyl-βCD (RAMEB) as the best carrier. Drug-RAMEB complexes were prepared by different techniques and were characterized for solid-state and dissolution properties. The best BTB-RAMEB product was chosen for entrapment in the aqueous core of deformable liposomes containing stearylamine, either alone or with sodium cholate, as edge activators. Double-loaded (DL) liposomes, bearing the lipophilic drug (0.5% w/v) in the bilayer and its hydrophilic RAMEB complex (0.5% w/v) in the aqueous core, were compared to single-loaded (SL) liposomes bearing 1% w/v plain drug in the bilayer. All vesicles showed homogeneous dimensions (i.e., below 300 nm), high deformability, and excellent entrapment efficiency. DL-liposomes were more effective than SL ones in limiting drug leakage (<5% vs. >10% after a 3 months storage at 4 °C). In vivo experiments in rabbits proved that all liposomal formulations significantly (p < 0.05) increased the intensity and duration of drug anesthetic action compared to its hydroalcoholic solution; however, DL liposomes were significantly (p < 0.05) more effective than SL ones in prolonging BTB anesthetic effect, owing to the presence of the drug-RAMEB complex in the vesicle core, acting as a reservoir. DL liposomes containing both edge activators were found to have the best performance.

Evaluation and Comparison of Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers (NLCs) as Vectors to Develop Hydrochlorothiazide Effective and Safe Pediatric Oral Liquid Formulations

The aim of this study was the optimization of solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) in terms of physicochemical and biopharmaceutical properties, to develop effective and stable aqueous liquid formulations of hydrochlorothiazide, suitable for paediatric therapy, overcoming its low-solubility and poor-stability problems. Based on solubility studies, Precirol® ATO5 and Transcutol® HP were used as solid and liquid lipids, respectively. The effect of different surfactants, also in different combinations and at different amounts, on particle size, homogeneity and surface-charge of nanoparticles was carefully investigated. The best formulations were selected for drug loading, and evaluated also for entrapment efficiency and release behaviour. For both SLN and NLC series, the use of Gelucire® 44/14 as surfactant rather than PluronicF68 or Tween® 80 yielded a marked particle size reduction (95-75 nm compared to around 600-400 nm), and an improvement in entrapment efficiency and drug release rate. NLC showed a better performance than SLN, reaching about 90% entrapped drug (vs. 80%) and more than 90% drug released after 300 min (vs. about 65%). All selected formulations showed good physical stability during 6-month storage at 4 °C, but a higher loss of encapsulated drug was found for SLNs (15%) than for NLCs (<5%). Moreover, all selected formulations revealed the absence of any cytotoxic effect, as assessed by a cell-viability test on Caco-2 cells and are able to pass the intestinal epithelium as suggested by Caco-2 uptake experiments.

Development and microbiological evaluation of chitosan and chitosan-alginate microspheres for vaginal administration of metronidazole

Metronidazole is the drug of choice in the treatment of bacterial vaginosis, but the oral therapy can induce several collateral effects. Aim of this work was the development of a vaginal multiparticulate system, loaded with metronidazole, able to improve its residence time allowing a complete drug release. Several kinds of MS were prepared using chitosan dissolved in different organic acids or alginate coated with chitosan. FTIR and DSC analyses were performed to study the interactions between the drug and the polymers, while MS morphology was investigated with optical and electron microscopy. All the formulations were characterized in terms of drug entrapment efficiency, mucoadhesion, swelling capacity and drug release behavior, demonstrating the best results for alginate MS coated with chitosan. The formulations evidenced a complete and rapid release of drug, compared with the commercial form: Zidoval®.The best formulations assayed for antibacterial activity confirmed the suitability of this new formulation for the vaginal treatment of local diseases.

Development and Characterization of Liquisolid Tablets Based on Mesoporous Clays or Silicas for Improving Glyburide Dissolution

The aim of this work was to evaluate the effectiveness of mesoporous clays or silicas to develop fast-dissolving glyburide tablets based on a liquisolid approach. Selected clay (Neusilin^®US2) and silica (Aeroperl^®300) allowed preparation of innovative drug liquisolid systems containing dimethylacetamide or 2-pyrrolidone as drug solvents, without using coating materials which are necessary in conventional systems. The obtained liquisolid powders were characterized for solid-state properties, flowability, compressibility, morphology, granulometry, and then used for directly compressed tablet preparation. The developed liquisolid tablets provided a marked drug dissolution increase, reaching 98% dissolved drug after 60 min, compared to 40% and 50% obtained from a reference tablet containing the plain drug, and a commercial tablet. The improved glyburide dissolution was attributed to its increased wetting properties and surface area, due to its amorphization/solubilization within the liquisolid matrix, as confirmed by DSC and PXRD studies. Mesoporous clay and silica, owing to their excellent adsorbent, flow, and compressibility properties, avoided use of coating materials and considerably improved liquid-loading capacity, reducing the carrier amount necessary to obtain freely flowing powders. Neusilin^®US2 showed a superior performance than Aeroperl^®300 in terms of the tablet’s technological properties. Finally, simplicity and cost-effectiveness of the proposed approach make it particularly advantageous for industrial scale-up.

Characterization and evaluation of different mesoporous silica kinds as carriers for the development of effective oral dosage forms of glibenclamide

This work evaluated the suitability of various mesoporous silicas as carriers for developing an oral formulation endowed with improved dissolution properties of glibenclamide, hypoglycemic agent poorly water-soluble. The different silicas were examined for solid-state, morphology, and technological and physical-chemical properties (granulometry, specific surface area, wettability, water content, water activity, apparent density, flowability, compactability). A pairwise comparison allowed a ranking, by importance order, of the parameters examined and, for each parameter, a score was assigned to each silica type. Data statistical treatment (JMP software) indicated Neusilin®US2 and Syloid®XDP3150 as the best materials. Different loading methods were tested: physical mixing; addition of drug dissolved in a volatile solvent, subsequently evaporated; addition of drug dissolved in a solvent. Methods involving drug dissolution enabled drug amorphization and intimate dispersion within the silica porous structure. Dissolution tests indicated Syloid®XDP3150 as the most effective silica in enhancing drug dissolution properties, providing a release rate clearly faster than from commercial tablets. Drug amorphization, improved wettability, increased surface area of the drug, finely dispersed into the highly porous silica, were the main factors responsible for this finding. Moreover, the obtained results suggested that drug dissolution rate can be properly tuned, based on the suited choice of the silica type.

Design, characterization and in vivo evaluation of nanostructured lipid carriers (NLC) as a new drug delivery system for hydrochlorothiazide oral administration in pediatric therapy

The hydrochlorothiazide (HCT) low solubility and permeability give rise to limited and variable bioavailability; its low stability makes it difficult to develop stable aqueous liquid formulations; its low dose makes the achievement of a homogeneous drug distribution very difficult. Thus, the aim of this study was to investigate the effectiveness of a strategy based on the development of nanostructured lipid carriers (NLC) as an innovative oral pediatric formulation of HCT with improved therapeutic efficacy. The performance of various synthetic and natural liquid lipids was examined and two different preparation methods were employed, i.e. homogenization-ultrasonication (HU) and microemulsion (ME), in order to evaluate their influence on the NLC properties in terms of size, polydispersity index, ζ-potential, entrapment efficiency, gastric stability, and drug release properties. Precirol®ATO5 was used as solid lipid and Tween^®80 and Pluronic^®F68 as surfactants, formerly selected in a previous study focused on the development of HCT-solid lipid nanoparticles (SLNs). The presence of Pluronic^®F68 did not allow ME formation. On the contrary, using Tween^®80, the ME method enabled a higher entrapment efficiency than the HU. Regardless of the preparation method, NLCs exhibited great entrapment efficiency values clearly higher than previous SLNs. Moreover, NLC-ME formulations provided a prolonged release, which lasted for 6 h. In particular, NLC-ME containing Tween^®20 as Co-Surfactant showed the best performances, giving rise to a complete drug release, never achieved with previous SLN formulations, despite their successful results. In vivo studies on rats confirmed these results, displaying their best diuretic profile. Moreover, all HCT-loaded NLC formulations showed higher stability than the corresponding SLNs.

Combined Approach of Cyclodextrin Complexationand Nanostructured Lipid Carriers for the Development of a Pediatric Liquid Oral Dosage Form of Hydrochlorothiazide

The development of specific and age-appropriate pediatric formulations is essential to assure that all children and their care-givers can easily access to safe and effective dosage forms. The need for developing specific pediatric medicinal products has been highlighted by the European Medicines Agency. The aim of this study was to investigate the effectiveness of combining the advantages of both cyclodextrin (CD) complexation and loading into nanostructured lipid carriers (NLC), to obtain a liquid oral pediatric formulation of hydrochlorothiazide (HCT), endowed with safety, dosage accuracy, good stability and therapeutic efficacy. Equimolar drug combinations as physical mixture (P.M.) or coground product (GR) with hydroxypropyl-β-cyclodextrin (HPβCD) or sulfobutylether-β-cyclodextrin (SBEβCD) were loaded into NLC, then characterized for particle size, homogeneity, Zeta potential, entrapment efficiency, gastric and storage stability. The presence of HPβCD allowed higher entrapment efficacy than NLC loaded with the plain drug, and enabled, in the case of GR systems a complete and sustained drug release, attributable to the wetting and solubilising properties of HPβCD toward HCT. In vivo studies on rats proved the superior therapeutic effectiveness of HCT-in HPβCD-in NLC formulations compared to the corresponding free HCT-loaded NLC, thus confirming the successfulness of the proposed approach in the development of an efficacious liquid oral formulation of the drug.

Comparison of liposomal and NLC (nanostructured lipid carrier) formulations for improving the transdermal delivery of oxaprozin: Effect of cyclodextrin complexation

The combined strategy of drug-cyclodextrin (CD) complexation and complex loading into nanocarriers (deformable liposomes or nanostructured lipid carriers (NLC)), was exploited to develop effective topical formulations for oxaprozin transdermal administration. Oxaprozin was loaded as ternary complex with randomly-methylated-ßCD and arginine, selected as the best system in improving drug solubility. The colloidal dispersions, characterized for particle size, zeta-potential and entrapment efficiency, were investigated for drug permeation properties in comparison with a plain drug aqueous suspension, a ternary complex aqueous solution and a plain drug liposomal or NLC dispersion. Experiments with artificial membranes showed that the joined use of CD and both liposomes or NLC enabled a marked increase of the drug permeability (16 and 8 times, respectively) and was significantly more effective (P<0.05) than the drug as ternary complex (3.2 times increase), and the corresponding liposomal or NLC dispersion of plain drug (5.6 and 4.3 times increase, respectively). Experiments with excised human skin confirmed the significantly (P<0.05) better performance of deformable liposomes than NLC in promoting drug permeation; moreover, they evidenced a more marked permeability increase compared to the plain drug (24 and 12 fold, respectively), attributed to a possible enhancer effect of the nanocarriers components and/or of the randomly-methylated-ßCD.

Analysis of physicochemical properties of ternary systems of oxaprozin with randomly methylated-ß-cyclodextrin and l-arginine aimed to improve the drug solubility

The influence of l-arginine on the complexing and solubilizing power of randomly-methylated-β-cyclodextrin (RameβCD) towards oxaprozin, a very poorly soluble anti-inflammatory drug, was examined. The interactions between the components were investigated both in solution, by phase-solubility analysis, and in the solid state, by differential scanning calorimetry, FTIR and X-ray powder diffractometry. The morphology of the solid products was examined by Scanning Electron Microscopy. Results of phase-solubility studies indicated that addition of arginine enhanced the RameβCD complexing and solubilizing power of about 3.0 and 4.5 times, respectively, in comparison with the binary complex (both at pH≈6.8). The effect of arginine was not simply additive, but synergistic, being the ternary system solubility higher than the sum of those of the respective drug-CD and drug-arginine binary systems. Solid equimolar ternary systems were prepared by physical mixing, co-grinding, coevaporation and kneading techniques, to explore the effect of the preparation method on the physicochemical properties of the final products. The ternary co-ground product exhibited a dramatic increase in both drug dissolution efficiency and percent dissolved at 60min, whose values (83.6 and 97.1, respectively) were about 3 times higher than the sum of those given by the respective drug-CD and drug-aminoacid binary systems. Therefore, the ternary co-ground system with arginine and RameβCD appears as a very valuable product for the development of new more effective delivery systems of oxaprozin, with improved safety and bioavailability.

Development of cyclodextrin hydrogels for vaginal delivery of dehydroepiandrosterone

Objective

To develop a new vaginal delivery system for a sustained release of dehydroepiandrosterone (DHEA) in the treatment of postmenopausal symptoms, aimed to overcome the problems of poor bioavailability of the drug related to its very low water solubility.

Methods

Cyclodextrin (CD)-containing hydrogels were developed, combining in a single device the hydrogel controlled release and mucoadhesion properties, and the CD solubilizing power towards DHEA. The effect of different CDs, alone or in mixtures, on the hydrogel technological and mucoadhesion characteristics was investigated. The best formulations were loaded with DHEA and characterized for loading efficiency and release properties.

Key findings

Hydrogels based on HPβCD/γCD (15/10%w/w) or HPβCD/HP γCD (30/20%w/w) combinations proved to be the most effective, giving ovules with the desired mechanical and mucoadhesive properties. Both formulations showed high drug loading efficiency, due to the solubilizing effect of CDs, and provided a sustained in-situ release, with a rate suitably tunable by varying the drug loaded amount and/or the CD combination.

Conclusions

The proposed formulative strategy allowed to develop an intravaginal device with right consistency and elasticity, easy to apply, able to be retained in situ over 8 h, and to provide an effective DHEA loading and a tunable release rate.

Combined use of bile acids and aminoacids to improve permeation properties of acyclovir

The aim of this work was to develop a topical formulation with improved permeation properties of acyclovir. Ursodeoxycholic (UDC) and dehydrocholic (DHC) acids were tested as potential enhancers, alone or in combination with different aminoacids. Equimolar binary and ternary systems of acyclovir with cholic acids and basic, hydrophilic or hydrophobic aminoacids were prepared by co-grinding in a high vibrational micromill. Differential scanning calorimetry (DSC) was used to characterize the solid state of these systems, while their permeation properties were evaluated in vitro through a lipophilic artificial membrane. UDC was more than 2 times more effective than DHC in improving drug AUC and permeation rate. As for the ternary systems drug-UDC-aminoacid, only the combined use of l-lysine with UDC acid produced an evident synergistic effect in enhancing drug permeation properties, enabling an almost 3 and 8 times AUC increase compared to the binary UDC system or the pure drug, respectively. The best systems were selected for the development of topical cream formulations, adequately characterized and tested for in vitro drug permeation properties and stability on storage. The better performance revealed by acyclovir-UDC-l-lysine was mainly attributed to the formation of a more permeable activated system induced by the multicomponent co-grinding process.

Development of liposomal and microemulsion formulations for transdermal delivery of clonazepam: effect of randomly methylated β-cyclodextrin

Transdermal administration of clonazepam, a poorly water-soluble benzodiazepine, is an interesting strategy for overcoming the drawbacks of its oral administration. With this aim, two nano-carrier formulations, based on ultra-deformable liposomes and microemulsions, have been developed to favour clonazepam transdermal delivery. Considering the solubilizing power of methyl-βcyclodextrin (Me-βCD) toward clonazepam and its potential positive influence on transdermal drug delivery, the effect of its addition to these formulations was investigated. Artificial lipophilic membranes simulating the skin allowed a rapid evaluation of the drug permeation properties from the systems, compared with those from an aqueous drug suspension, with or without Me-βCD. The best formulations were further characterized by permeation through excised rabbit ear skin. All the formulations increased drug permeability, ranging from 2-fold (liposomes without Me-βCD), up to over 4-fold (microemulsions containing Me-βCD). The different formulations allowed for pointing out different possible permeation enhancing mechanisms of Me-βCD: increase in drug solubility and thermodynamic activity in the vehicle, when added to the drug aqueous suspension; interactions with the vesicle bilayer, in case of liposomal formulations; interactions with the skin membrane lipids, as evidenced in experiments with excised rabbit ear for microemulsions containing Me-βCD, that were then selected for further in vivo studies.

Development of a new delivery system consisting in "drug--in cyclodextrin--in nanostructured lipid carriers" for ketoprofen topical delivery

A new delivery system based on drug cyclodextrin (Cd) complexation and loading into nanostructured lipid carriers (NLC) has been developed to improve ketoprofen therapeutic efficacy. The proposed strategy exploits both the solubilizing and stabilizing properties of Cds and the prolonged release, high tolerability and percutaneous absorption enhancer properties of NLC. Two different polymeric Cds, i.e. β-Cd-epichlorohydrin polymer (EPI-βCd) and carboxymethylathed-β-Cd-epichlorohydrin polymer (EPI-CMβCd) were tested and two different techniques to obtain solid ketoprofen-polymeric Cd complexes (i.e. co-grinding and co-lyophilization) were compared, to investigate the influence of the preparation method on the physicochemical properties of the end product. EPI-βCd was more effective than EPI-CMβCd in enhancing the solubility and dissolution properties of ketoprofen. Co-grinding in dry conditions was the best preparation technique of solid drug-Cd systems, allowing obtainment of homogeneous amorphous particles of nanometric range. NLC consisting in a mixture of Compritol® 888 ATO (glyceryl behenate) and Labrafac Lipophile were obtained by ultrasonication. Both empty and loaded NLC were suitably characterized for particle size, pH, entrapment efficiency and drug release behavior. The best (drug-Cd)-loaded NLC system, formulated into a xanthan hydrogel, exhibited drug permeation properties clearly better than those of the plain drug suspension or the plain drug-loaded NLC, in virtue of the simultaneous exploitation of the solubilizing effect of cyclodextrin and the penetration enhancer properties of NLC.

Improvement of oxaprozin solubility and permeability by the combined use of cyclodextrin, chitosan, and bile components

The effect of the combined use of randomly methylated β-cyclodextrin (RAMEB), chitosan (CS), and bile components (dehydrocholic (DHCA) or ursodeoxycholic (UDCA) acids and their sodium salts) on solubility and permeability through Caco-2 cells of oxaprozin (a very poorly water-soluble non-steroidal anti-inflammatory drug) has been investigated. Addition of CS, bile acids, and their sodium salts increased the RAMEB solubilizing power of 4, 2, and 5 times, respectively. Drug-RAMEB-CS co-ground systems showed very higher dissolution rate than corresponding drug-RAMEB systems. Addition of bile components further improved drug dissolution rate. The CS presence enabled a significant increase in drug permeability through Caco-2 cells with respect to drug-RAMEB systems. Moreover, CS and NaDHC showed a synergistic enhancer effect, enabling a 1.4-fold permeability increase in comparison with systems without bile salt. However, unexpectedly, no significant differences were found between physical mixtures and co-ground products, indicating that drug permeation improvement was due to the intrinsic enhancer effect of the carriers and not to drug-carrier interactions brought about by co-grinding, as instead found in dissolution rate studies. The combined use of RAMEB, CS, and NaDHC could be exploited to develop effective oral dosage forms of oxaprozin, with increased drug solubility and permeability, and then improved bioavailability.

Development of mucoadhesive films for buccal administration of flufenamic acid: Effect of cyclodextrin complexation

A new mucoadhesive film for topical administration in the oral cavity of flufenamic acid, a poorly soluble anti-inflammatory drug, has been developed, using complexation with hydroxypropyl-beta-cyclodextrin (HPbetaCD) to improve drug dissolution and release rate. Buccal films were prepared utilising chitosan as mucoadhesive polymer, KollicoatIR as film-forming polymer and glycerol as plasticiser. Different combinations of these components were used and the obtained films were characterised for weight, thickness, swelling, mucoadhesive and mechanical properties. The film containing chitosan 2%, glycerol 7.5% and KollicoatIR 1% showed the best properties for the development of the film formulation. The selected film was loaded with the plain drug and its colyophilised and coground products with HPbetaCD, and in vitro release studies in simulated saliva were performed. The improved drug dissolution properties, obtained by complexation with HPbetaCD, were critical to achieve complete release from film formulation during 4-5 h. On the contrary, film loaded with the plain drug showed incomplete release, not exceeding 70% release after 5 h. The developed film formulation containing the drug as complex with HPbetaCD can assure a prolonged drug release directly at the inflammation site and can be proposed as a new therapeutic tool in the treatment of oral mucosa inflammations.

Physical-chemical characterization of binary and ternary systems of ketoprofen with cyclodextrins and phospholipids

Binary and ternary interaction products of ketoprofen (an anti-inflammatory drug very poorly water soluble) with phospholipids (phosphatidylcholine (EPC3) and phosphatidylglycerol (EPG)) and cyclodextrins (beta-cyclodextrin and its methylated derivative (MebetaCd)), were prepared to evaluate their ability in improving drug dissolution properties. The different binary and ternary drug-carrier(s) systems were obtained by microwave irradiation, in order to investigate the effectiveness of such a newly proposed preparation technology in bringing about effective solid-state interactions among the components. The effect of different experimental conditions such as microwave irradiation power (500 and 750 W) and treatment time (5, 10 and 15 min) on the physicochemical properties of the products has been also assessed. All solid systems were characterized by differential scanning calorimetry (DSC) analysis, supported by X-ray powder diffractometry, and examined for dissolution properties. The study pointed out the better performance of ternary systems than the binary ones and allowed selection of the best drug-phospholipid-Cd combination and of the most effective preparation conditions. In particular drug-EPC3-MebetaCd ternary systems obtained by using the greatest microwave irradiation energy and the longest treatment time exhibited complete drug amorphization and allowed achievement after 60 min of almost 80% dissolved drug, with an increase in dissolution efficiency of 10.7 and 1.4 times in comparison with drug alone and the corresponding drug-Cd binary system, respectively. The synergistic effect between cyclodextrin and phospholipid in enhancing the drug dissolution properties has been attributed to the combination of the surfactant properties of phospholipids and the wetting and solubilizing power of cyclodextrins and/or the possible formation of a "multicomponent" complex.

Development of Enteric-coated Pectin-based Matrix Tablets for Colonic Delivery of Theophylline

The present work was aimed at developing a new colonic drug delivery system which takes advantage of the combined approaches of a specifically colon-biodegradable pectin matrix with a pH-sensitive Eudragit S100 polymeric coating. The developed system was able to suitably retard the onset of drug release and to provide a colon-specific delivery, thus overcoming the problems of pectin solubility in the upper gastrointestinal tract and low site-specificity of simple pH-dependent systems. Due to the poor compactability properties of pectin, it was used in mixture with Emdex, a hydrophilic directly-compressible material, in order to make it possible to prepare tablets by direct compression. Theophylline (TP) was used as model drug due to its suitable pharmacokinetic properties for colonic delivery and good absorption in the large intestine. The effects of varying the type of pectin (low and high methoxylated, or amidated), the pectin:Emdex ratio and the level of the pH-dependent polymeric coating on drug release behavior were investigated. Release tests were performed using sequential liquids simulating the physiological variation of pH and the effect of the presence or not of pectinolytic enzymes into the simulated colonic medium was evaluated. Thirty percent (w/w) was the the minimum content of Emdex for obtaining directly compressible tablets with sufficient hardness to withstand the coating process and 27% (w/w) was the minimum coating amount for obtaining an adequate lag time before the onset of drug release. After lag time, linear nearly zero-order profiles were obtained whose slope (i.e. the drug release rate) depended on both the Emdex content and the pectin type. Comparison of the results obtained in the presence or not of pectynolitic enzymes allowed selection of the high methoxylated pectin as the most interesting candidate for specific colonic delivery since it was the least water-soluble and the most susceptible to enzymatic degradation, thus assuring a greater site-specificity of drug release. Finally, the importance of using appropriate dissolution test conditions to adequately characterize the drug release profiles from delivery systems endowed with a microflora-activated drug release triggering mechanism has been demonstrated.

Development of Enteric-coated Timed-release Matrix Tablets for Colon Targeting

A new oral drug delivery system for colon targeting has been developed based on enteric-coated matrix tablets which suitably exploits both pH-sensitive and time-dependent functions. Matrix-tablets were prepared by direct compression of mixtures of hydroxyethylcellulose (HEC), a hydrophilic swellable polymer, with the inert insoluble ethylcellulose (EC) or micro-crystalline cellulose (MCC) polymers, in which theophylline, selected as model drug, was dispersed. Eudragit S100, a methacrylic acid copolymer soluble at pH 7, was used as pH-sensitive coating polymer. The influence of varying the cellulose-derivative combinations and their relative ratios as well as the level of the coating polymer was investigated. Surface morphology of the tablets was monitored by SEM analysis before and after the release test. The results of release studies, performed according to the USP basket method using a sequence of dissolution media simulating the gastrointestinal physiological pH variation, indicated that the Eudragit S100 enteric-coated matrix tablets were successful in achieving gastric resistance and timed-release of the drug, assuring an adequate lag time for the intended colonic targeting, followed by a controlled-release phase. The enteric-coating level emerged as the critical factor in determining the duration of the lag-phase, whereas the release rate mainly depended on the matrix composition. Formulations with higher HEC content showed a faster drug release rate than those with greater content in inert polymer and the MCC-HEC combinations were more effective than the corresponding EC-HEC ones. The best results were given by the 27% coated 1:0.3:0.7 (w/w) drug/MCC/HEC tablets, which, after a 260 min lag time, regularly released the drug, achieving about 90% of release after 10 h.

Development of Fast-Dissolving Tablets of Flurbiprofen-Cyclodextrin Complexes

The present study was aimed at developing a tablet formulation based on an effective flurbiprofen-cyclodextrin system, able to allow a rapid and complete dissolution of this practically insoluble drug. Three different cyclodextrins were evaluated: the parent beta-cyclodextrin (previously found to be the best partner for the drug among the natural cyclodextrins), and two amorphous, highly soluble beta-cyclodextrin derivatives, i.e., methyl-beta-cyclodextrin and hydroxyethyl-beta-cyclodextrin. Equimolar drug-cyclodextrin binary systems prepared according to five different techniques (physical mixing, kneading, sealed-heating, coevaporation, and colyophilization) were characterized by Differential Scanning Calorimetry, x-ray powder diffractometry, infrared spectroscopy, and optical microscopy and evaluated for solubility and dissolution rate properties. The drug solubility improvement obtained by the different binary systems varied from a minimum of 2.5 times up to a maximum of 120 times, depending on both the cyclodextrin type and the system preparation method. Selected binary systems were used for preparation of direct compression tablets with reduced drug dosage (50 mg). Chitosan and spray-dried lactose, alone or in mixture, were used as excipients. All formulations containing drug-cyclodextrin systems gave a higher drug dissolved amount than the corresponding ones with drug alone (also at a dose of 100 mg); however, the drug dissolution behavior was strongly influenced by formulation factors. For example, for the same drug-cyclodextrin product the time to dissolve 50% drug varied from less than 5 minutes to more than 60 minutes, depending on the excipient used for tableting. In particular, only tablets containing the drug kneaded with methyl-beta-cyclodextrin or colyophilized with beta-cyclodextrin and spray-dried lactose as the only excipient satisfied the requirements of the Food and Drug Administration (FDA) for rapid dissolving tablets, allowing more than 85% drug to be dissolved within 30 minutes. Finally, it can be reasonably expected that the obtained drug dissolution rate improvement will result in an increase of its bioavailability, with the possibility of reducing drug dosage and side effects.

Characterization and Dissolution Properties of Ketoprofen in Binary and Ternary Solid Dispersions with Polyethylene Glycol and Surfactants

The effect of incorporation of an anionic [sodium dodecyl sulfate (SDS) or dioctylsulfosuccinate (DSS)] or nonionic [Tween 60 (TW60)] surfactant on the properties of ketoprofen solid dispersions in polyethylene glycol 15000 (PEG) has been investigated. Physicochemical and morphological properties of the various solid systems were determined by differential scanning calorimetry, hot stage microscopy, X-ray powder diffraction analysis, and scanning electron microscopy. The results from dissolution studies, performed according to the USP 24 basket method, indicated that all ternary dispersed systems were significantly (p < 0.001) more efficacious than the corresponding binary ones, by virtue of the additive wetting and solubilizing effect due to the presence of the surfactant. The relative effectiveness of the incorporated surfactant was in the same order as found in phase-solubility studies (i.e., SDS > DSS > TW60). With regard to the solid dispersion preparation method, coevaporated products always gave better results than the corresponding cofused ones; however, this effect was statistically significant (p < 0.001) only in the initial phase of the dissolution process. The most effective solid dispersion was the 10-80-10 w/w drug-PEG-SDS ternary coevaporate, which allowed dissolution of 50% drug after only 6 min (in comparison with > 120 min for drug alone and 17 min for the binary coevaporate) and dissolution of about 100% drug after 30 min (in comparison with > 120 min for the binary coevaporate).

Physical–chemical characterization of binary systems of metformin hydrochloride with triacetyl-β-cyclodextrin

Interaction products of metformin hydrochloride (MF.HCl), an oral anti-hyperglycaemic agent highly soluble in water, with triacetyl-beta-cyclodextrin (TAbetaCyD), a hydrophobic CyD derivative practically insoluble in water, were prepared to evaluate their suitability for the development of a sustained-release dosage form of the drug. Equimolar MF.HCl-TAbetaCyD solid compounds were obtained by different techniques, i.e., physical mixing, kneading, co-grinding, sealed-heating, and spray-drying, in order to investigate and compare their effectiveness and influence on the physical-chemical properties of the final products. Differential scanning calorimetry, X-ray powder diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy were used for the solid-state characterization of the different MF.HCl-TAbetaCyD systems, whereas their in vitro dissolution properties were determined according to the dispersed amount method. According to the results of solid-state studies, the ability of the different preparation methods to promote effective interactions between drug and CyD varied in the order: spray-drying>co-grinding>kneading>sealed-heating approximately physical mixing. The same effectiveness rank order was observed also in dissolution studies. In fact the time to dissolve 100% drug varied increased from 1 min, for pure drug, to 3, 7, 40, 120 up to 420 min for physically mixed, sealed-heated, kneaded, co-ground and spray-dried products, respectively. Thus the drug-TA(CyD products obtained by spray drying and co-grinding were selected as the best candidates for the future development of a suitable prolonged-release oral dosage form of MF.HCl.

Liquid spray formulations of xibornol by using self-microemulsifying drug delivery systems

Xibornol is a lipophilic drug mainly used in Italy and Spain in spray dosage forms for the local treatment of infection and inflammation of the throat. Its poor water solubility makes difficult the development of aqueous formulations of the drug, thus giving rise to a limited number of stable and pharmaceutically accepted preparations. In fact, xibornol is actually marketed only as spray aqueous suspension. The aim of this work was to evaluate the possibility of developing a stable liquid formulation of the drug intended for oral spray administration using a self-microemulsifying drug delivery system (SMEDDS). These systems are able to adequately improve the drug solubility, allowing the introduction of relatively high concentration of drugs in the form of solution. Labrafil M1944, Labrafil M2125 and Labrafac CC were screened as oil phases, Labrasol and Labrafac PG as surfactants and Transcutol as co-surfactant. Pseudo-ternary phase diagrams were constructed, by titration with the aqueous phase of different oil phases and surfactant/co-surfactant mixtures in order to identify the self-microemulsification region and the optimal micro-emulsion composition. Then, complete pharmaceutical formulations were prepared and evaluated for stability and viscosity properties. The final selected formulations, containing Labrafil M1944, Transcutol, Labrafac PG and a hydrophilic co-solvent (propylene glycol or PEG 200) allowed complete solubilization of the required xibornol concentration (3%, w/v) and showed physical good stability up to 2 months at 25 and 4 degrees C, suitable viscosity and organoleptic properties.

Fast-dissolving tablets of glyburide based on ternary solid dispersions with PEG 6000 and surfactants

Marketed glyburide tablets present unsatisfying dissolution profiles that give rise to variable bioavailability. With the purpose of developing a fast-dissolving tablet formulation able to assure a complete drug dissolution, we investigated the effect of the addition to a reference tablet formulation of different types (anionic and nonionic) and amounts of hydrophilic surfactants, as well as the use of a new technique, based on ternary solid dispersions of the drug with an hydrophilic carrier (polyethylene glycol [PEG] 6000) and a surfactant. Tablets were prepared by direct compression or previous wet granulation of suitable formulations containing the drug with each surfactant or drug:PEG:surfactant ternary dispersions at different PEG:surfactant w/w ratios. The presence of surfactants significantly increased (p<0.01) the drug dissolution rate, but complete drug dissolution was never achieved. On the contrary, in all cases tablets containing ternary solid dispersions achieved 100% dissolved drug within 60 min. The best product was the 10:80:10 w/w ternary dispersion with PEG 6000 and sodium laurylsulphate, showing a dissolution efficiency 5.5-fold greater than the reference tablet formulation and 100% drug dissolution after only 20 min.

Sustained-release matrix tablets of metformin hydrochloride in combination with triacetyl-beta-cyclodextrin

The low bioavailability and short half-life of metformin hydrochloride (MH) make the development of sustained-release forms desirable. However, drug absorption is limited to the upper gastrointestinal (GI) tract, thus requiring suitable delivery systems providing complete release during stomach-to-jejunum transit. This study was undertaken to develop a MH sustained-release formulation in compliance with these requirements. The strategy proposed is based on direct-compressed matrix tablets consisting of a combination of MH with the hydrophobic triacetyl-beta-cyclodextrin (TAbetaCD), dispersed in a polymeric material. Different polymers were tested as excipients, i.e. hydroxypropylmethylcellulose, xanthan gum, chitosan, ethylcellulose, Eudragit L100-55, and Precirol. Compatibility among the formulation components was assessed by DSC analysis. All the tablets were examined for drug release pattern in simulated gastric and jejunal fluids used in sequence to mimic the GI transit. Release studies demonstrated that blends of a hydrophobic swelling polymer (hydroxypropylmethylcellulose or chitosan) with a pH-dependent one (Eudragit L100-55) were more useful than single polymers in controlling drug release. Moreover, the main role played by the MH-TAbetaCD system preparation method (i.e. grinding or spray-drying) in determining the behaviour of the final formulation was evidenced. In fact, for a given matrix-tablet composition, different sustained-release effects were obtained by varying the relative amounts of MH-TAbetaCD as ground or spray-dried product. In particular, the 1:1 (w/w) blend of such systems, dispersed in a Eudragit-chitosan polymeric matrix, fully achieved the prefixed goal, giving about 30% released drug after 2h at gastric pH, and overcoming 90% released drug within the subsequent 3h in jejunal fluid.

Simultaneous effect of cyclodextrin complexation, pH, and hydrophilic polymers on naproxen solubilization

The effect of pH variation on complexation and solubilization of naproxen (pK(a) 4.2) with natural betaCyclodextrin (betaCyD) and various neutral, cationic and anionic betaCyD-derivatives has been investigated. The combined effect of pH variation and hydrophilic polymer addition on CyD solubilizing and complexing efficiency has also been determined. Phase-solubility analysis in buffered aqueous solutions (pH from 1.1 to 6.5) was used to study the interaction of the drug with each CyD, in the presence or not of the water-soluble polymer. A clear influence of the substituent type was observed, the methylderivative being the most efficient agent; on the contrary, unexpectedly, no influence of the CyD charge in the interaction with the ionizable drug was detected. As expected, total drug solubility increased with increasing pH; however, the solubility increment with respect to drug alone obtained by CyD complexation progressively decreased, with a parallel reduction of the complex stability, attributed to the reduced affinity of charged drug for the hydrophobic CyD cavity. The addition of the polymer in part counterbalanced the destabilizing effect obtained with increasing pH, by improving the CyD complexation power towards naproxen. In particular, the presence of PVP allowed an increase of the complex stability constant with hydroxypropyl betaCyD up to 60% with respect to the corresponding drug-CyD binary system. Therefore, the combined strategy of pH control and polymer addition to the CyD complexing medium can be successfully exploited to improve naproxen solubilization and reduce the amount of CyD needed. The construction of theoretical drug solubility curves as a function of pH for any given CyD and polymer concentration enables selection of the best experimental conditions for obtaining the desired drug solubility value.

Differential scanning calorimetry as a screening technique in compatibility studies of DHEA extended release formulations

Differential scanning calorimetry (DSC) was used as a screening technique for assessing the compatibility of DHEA as ternary complex with alpha-cyclodextrin and glycine (c-DHEA) with some excipients suitable for preparation of sustained-release matrix tablets by direct compression. The effect of sample mechanical treatment due to the compression process was also evaluated. In order to investigate the possible interactions between the components, the DSC curves of c-DHEA and each selected excipient were compared with those of their 1:1 w/w physical mixtures, before and after compression, in order to evaluate any possible solid state modification. FT-IR spectroscopy and X-ray powder diffractometry were used as complementary techniques to adequately implement and assist in interpretation of the DSC results. On the basis of DSC results, c-DHEA was found to be compatible with xanthan gum, hydroxypropylmethylcellulose, sodium starch glycolate (Explotab), polyvinylacetate-polyvinylpirrolidone (Kollidon SR) and sodium chloride. Some drug-excipient interaction was observed with dextrate hydrate (Emdex), mannitol and Magnesium stearate. Finally, the behaviour of the complete formulation, in the presence of all the excipients selected by means of the compatibility study, was investigated, in order to verify the absence of reciprocal interactions among the components.

Development and evaluation of an in vitro method for prediction of human drug absorption

A study was undertaken aimed at developing a dynamic in vitro method based on the use of artificial membranes for screening and prediction of the absorption properties of drugs. The development of a suitable artificial membrane simulating the behaviour of the natural gastrointestinal one is the critical step for the fulfillment of this research and it has been the aim of the present work. A series of filters of different chemical nature and different characteristics (pore size, percent of porosity, thickness) were evaluated and compared in order to select the most suitable one to use as support for the artificial lipid membrane preparation. Permeation experiments were performed by using naproxen as reference model drug. The target was to achieve a naproxen apparent permeability (P(app)) value close to that previously obtained using a Caco-2 cell dynamic methodology (4.88 x 10(-5)cms(-1)), which related well to the fraction of dose absorbed in vivo in human. Filters of cellulose nitrate-acetate mixture with a porosity of 70% and 0.025 microm pore size were selected on the basis of the highest reproducibility of results and suitable drug P(app) value obtained. Mixture design experiments were then carried out in order to optimize the composition of the lipid mixture to use for porous support impregnation to obtain the desired P(app) value. Sixteen different lipid mixtures were prepared according to mixture experimental plan and evaluated by diffusion experiments. The contour plot obtained was used to select an optimum lipidic mixture (cholesterol 2.10%; Lipoid((R)) E 80 1.70%; n-octanol 96.2%) for the cellulose nitrate-acetate membrane impregnation. The experimental response obtained from diffusion experiments performed by utilising the optimised lipidic impregnation mixture, was 4.88 x 10(-5)cms(-1), matching exactly the prefixed target.

Interaction of naproxen with ionic cyclodextrins in aqueous solution and in the solid state

The possible role of the cyclodextrin charge in the interaction with an acidic drug such as naproxen (pKa 4.8) has been evaluated. Sulfobutylether-beta-cyclodextrin (SBE-betaCyd) and trimethylammonium-beta-cyclodextrin (TMA-betaCyd) were selected as, respectively, anionically and cationically charged carriers and their performance was compared with that of the parent beta-cyclodextrin (betaCyd) and of its methyl-derivative (Me betaCyd) previously found as the best partner for the drug. Interactions in solution were investigated by phase-solubility, fluorescence and circular dichroism analyses. Equimolar drug-carrier products prepared by different techniques (blending, cogrinding, sealed-heating, colyophilization) were characterized by differential scanning calorimetry and X-ray powder diffractometry and tested for drug dissolution properties. Anionic charges of SBE-betaCyd did not negatively influence interactions in unbuffered aqueous solutions (pH approximately 5) with the acidic drug. In fact, it was a very effective carrier, exhibiting solubilizing and complexing properties considerably better than the parent betaCyd and comparable to those of Me betaCyd. On the contrary, the positive charges of TMA-betaCyd did not favour interactions with the counter-ionic drug (despite the presence of about 60% ionised drug) and it was less efficacious also than native betaCyd. Therefore, the role of the Cyd charge on the complexing and solubilizing properties towards naproxen was not important whereas other factors, such as steric hindrance effects and favourable hydrophobic interactions were significant in determining the drug affinity for the Cyd inclusion. Solid state studies evidenced similar amorphizing properties of both charged Cyds towards naproxen. On the other hand, dissolution tests, in agreement with solution studies, showed that all products with SBE-betaCyd exhibited significantly better dissolution properties than the corresponding ones with TMA-betaCyd. A clear influence of the preparation method of drug-Cyd solid systems on the performance of the end product was also observed. Colyophilization was the most effective technique, followed by the cogrinding one. Colyophilized product with SBE-betaCyd allowed a 10-times increase in drug dissolution efficiency (D.E.) (with respect to the five-times increase obtained with the corresponding coground product) and a reduction of t(50%) from about 60 min (for the coground product) to less than 2 min.

Determination of stability constant values of flurbiprofen-cyclodextrin complexes using different techniques

Three new experimental approaches for calculating the stability constant (K(st)) of complexes of flurbiprofen with natural beta-cyclodextrin (betaCyd) and the hydroxyethyl- (HEbetaCyd) and the methyl- (Me betaCyd) derivatives were tested and compared to the classic phase-solubility procedure: (a) the membrane permeation technique through a lipophilic synthetic membrane permeable to the drug but not to the Cyd molecules, by analysing the permeation profiles with a non-linear least-squares method; (b) the affinity capillary electrophoresis (ACE) technique, where K(st) were calculated from the relationship between Cyd concentration in solution and drug electrophoretic mobility, using three different linear plotting methods; (c) the molecular modeling technique, based on the relationship between the docking energies and the experimental K(st) values. The study allowed evaluation of the advantages and limits of each examined method, providing a useful guide for the choice of the most suitable one depending on the kind of host-guest system to be investigated. The K(st) values obtained with the various techniques were rather different, probably due to the very different experimental conditions required by each one. However, all the methods indicated the methyl-derivative as the most powerful complexing agent for the drug, showing the general trend: K(st)(Me betaCyd)>>K(st)(HEbetaCyd)>K(st)(betaCyd). Only in the case of the ACE method was an inversion of the trend found between HEbetaCyd and betaCyd; this was probably due to the lower molecular weight of the natural Cyd, which, in this case, became more important in determining the complex electrophoretic mobility than the different affinity of the drug for these two Cyds.

Study of formulation variables influencing the drug release rate from matrix tablets by experimental design

Experimental design was utilized to simultaneously investigate the effect of varying the type of diluent (insoluble Calcium phosphate or water-soluble arabic gum) and the diluent/matrix ratio on the drug release behaviour from both lipophilic (glyceryl behenate, Compritol) or hydrophilic (hydroxypropylmethylcellulose) matrix tablets. Ketoprofen, theophylline and sodium sulphadiazine were selected as model drugs on the basis of their respectively very low, medium and high water-solubility, in order to evaluate the influence of this parameter as well. The selected response variables were the dissolution efficiency (i.e. the area under the dissolution curve) after one and six hours and the time necessary to dissolve 10% drug. Tablets obtained by direct compression of drug-diluent-matrix ternary mixtures prepared according to the experimental plan provided for by an asymmetric screening matrix, were tested for drug release properties using a USP paddle apparatus. Graphic analysis of the effects allowed identification, for each examined drug, of the formulation factors active on the selected responses and determination of the proper level of the variables to be selected for the response improvement. The different results obtained with the three examined drugs pointed out the role of the drug solubility in determining the influence of formulation parameters on drug release rate from matrix tablets.