International Journal of Pharmaceutics (v.336, #1)

In this article, we present a parallel experimentation approach to rapidly identify a solubility-enhancing formulation that improved the bioavailability of a poorly water-soluble compound using milligrams of material. The lead compound and a panel of excipients were dissolved in n-propanol and dispensed into the wells of a 96-well microtiter plate by a TECAN robot. Following solvent evaporation, the neat formulations were diluted with an aqueous buffer, and incubated for 24 h. The solubilization capacity of the excipients for the compound at 24 h (SC24 h), was determined by HPLC, and compared with its solubility in the corresponding neat formulations determined by a bench-scale method. The ranking order of solubilization capacity of the five tested formulations for this compound by this microscreening assay is same as the ranking order of the compound solubility in the neat formulations. Several formulations that achieved the target aqueous solubility were identified using the screening method. One of the top formulations, an aqueous solution of the compound containing 20% Tween® 80 by weight, increased the compound solubility from less than 2 μg/mL to at least 10 mg/mL. In a rat pharmacokinetic (PK) study, the Tween® 80 formulation achieved 26.6% of bioavailability, a significant improvement over 3.4% of bioavailability for the aqueous Methocel® formulation (p  < 0.01). The results in the study suggest that this parallel screening assay can be potentially used to rapidly identify solubility-enhancing formulations for an improved bioavailability of poorly water-soluble compounds using milligram quantities of material.
Keywords: Parallel formulations screening; High-throughput formulation screening; Solubilization; Poorly water-soluble compounds; Bioavailability;

Cornea is considered as a major barrier for ocular drug delivery. Low ocular bioavailability of drugs has been attributed primarily to low permeability across corneal epithelium, thus leading to sub-therapeutic concentrations of drug in the eye and treatment failure. The role of drug efflux proteins, particularly the P-glycoprotein (P-gp) in ocular drug bioavailability has been reported. The objective of this research was to determine whether human corneal epithelium expresses multidrug resistance associated proteins (MRPs) contributing to drug efflux by employing both cultured corneal cells and freshly excised rabbit cornea. SV40-HCEC and rPCEC were selected for in vitro testing. SV40-HCEC and freshly excised rabbit corneas were utilized for transport studies. [3H]-cyclosporine-A and [14C]-erythromycin, which are known substrates for ABCC2 and MK-571, a specific inhibitor for MRP were applied in this study. RT-PCR indicated a unique and distinct band at ∼272 bp corresponding to ABCC2 in HCEC, SV40-HCEC, rabbit cornea, rPCEC, and MDCKII-MRP2 cells. Also RT-PCR indicated a unique band ∼181 bp for HCEC and SV40-HCEC. Immunoprecipitation followed by Western Blot analysis revealed a specific band at ∼190 kDa in membrane fraction of SV40-HCEC, MDCKII-MRP2 and no band with isotype control. Uptake of [3H]-cyclosporine-A and [14C]-erythromycin in the presence of MK-571 was significantly enhanced than control in both SV40-HCEC and rPCEC. Similarly a significant elevation in (A   B) permeability of [3H]-cyclosporine-A and [14C]-erythromycin was observed in the presence of MK-571 in SV40-HCEC. A   B transport of [3H]-cyclosporine-A was elevated in the presence of MK-571 in freshly excised rabbit cornea indicating potential role of this efflux transporter and high clinical significance of this finding.
Keywords: Multidrug resistance associated protein (MRP); Human corneal epithelial cell; Specific MRP inhibitor; Ocular drug efflux;

Preparation of glass solutions of three poorly water soluble drugs by spray drying, melt extrusion and ball milling by James E. Patterson; Michael B. James; Angus H. Forster; Robert W. Lancaster; James M. Butler; Thomas Rades (22-34).
The aim of this study was to investigate the influence of the manufacturing process on the physicochemical properties of three poorly water soluble compounds (carbamazepine, dipyridamole, and indomethacin) when processed with a polymer (polyvinylpyrrolidone K30 (PVP)) at a 1:2 drug to polymer ratio. Melt extrusion, spray drying, and ball milling techniques were used to prepare glass solutions. Product homogeneity, dissolution, physical stability, and drug/polymer interactions were investigated. Particular attention was paid to solid phase analysis using XRPD, modulated temperature DSC, optical microscopy, and Raman microscopy and the importance of using a combination of techniques was demonstrated. The latter technique when applied to freshly ball milled samples exhibited the presence of drug and polymer rich areas, indicating that complete glass solution formation had not occurred. The three compounds produced products with differing physical stability with indomethacin proving the most physically stable. These differences in physical stability were attributed to hydrogen bonding of drug and polymer. The manufacturing technique did not influence physical stability, but it did affect dissolution. The dissolution of the spray-dried material was generally poor, compared to melt extruded and ball milled products. This was probably due to rapid dissolution of PVP from the small particles of the spray-dried products.
Keywords: Glass solutions; Spray drying; Milling; Melt extrusion; Indomethacin; Carbamazepine; Dipyridamole; Poly(vinylpyrrolidone);

Stacking complexation by nicotinamide: A useful way of enhancing drug solubility by Ritesh Sanghvi; Daniel Evans; Samuel H. Yalkowsky (35-41).
The solubility enhancement of 11 poorly soluble drugs by complexation using nicotinamide has been studied. The solubilization efficiency of nicotinamide has been compared to that of hydroxypropyl-β-cyclodextrin and sulfobutylether-β-cyclodextrin. Solubility enhancements as high as 4000-fold are observed in 20% (w/v) nicotinamide solution. Furthermore, nicotinamide is more effective than cyclodextrins for solubilizing some of the drugs. The mechanism of drug solubilization by nicotinamide is investigated by studying the effects of nicotinamide concentration on the surface tension and the conductivity of water. A slight break in both, the surface tension and conductivity is noticed at around 10% (w/v), suggesting self-association at higher concentrations. Corresponding breaks in the solubility profiles of estrone and griseofulvin at similar concentrations support self-association. Based on this observation it appears that at low concentrations, one molecule of nicotinamide undergoes complexation with one drug molecule to form a 1:1 complex. At higher concentrations, two molecules of nicotinamide undergo complexation with one drug molecule forming a 1:2 complex. The complexation constants have been calculated for all the drugs and the data are well described by this model. Expectedly, increasing the temperature reduces the complexation constants.
Keywords: Nicotinamide; Solubilization; Stacking; Self-association;

Polymer-mediated disruption of drug crystallinity by Clare F. Rawlinson; Adrian C. Williams; Peter Timmins; Ian Grimsey (42-48).
Ibuprofen (IB), a BCS Class II compound, is a highly crystalline substance with poor solubility properties. Here we report on the disruption of this crystalline structure upon intimate contact with the polymeric carrier cross-linked polyvinylpyrrolidone (PVP-CL) facilitated by low energy simple mixing. Whilst strong molecular interactions between APIs and carriers within delivery systems would be expected on melting or through solvent depositions, this is not the case with less energetic mixing. Simple mixing of the two compounds resulted in a significant decrease in the differential scanning calorimetry (DSC) melting enthalpy for IB, indicating that approximately 30% of the crystalline content was disordered. This structural change was confirmed by broadening and intensity diminution of characteristic IB X-ray powder diffractometry (PXRD) peaks. Unexpectedly, the crystalline content of the drug continued to decrease upon storage under ambient conditions. The molecular environment of the mixture was further investigated using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopy. These data suggest that the primary interaction between these components of the physical mix is hydrogen bonding, with a secondary mechanism involving electrostatic/hydrophobic interactions through the IB benzene ring. Such interactions and subsequent loss of crystallinity could confer a dissolution rate advantage for IB.
Keywords: Ibuprofen; Polyvinylpyrrolidone; Amorphous; Hydrogen bonding; Physical mixing; Solid dispersion;

Self-association behavior of polypeptide graft copolymer and its mixture with polypeptide block copolymer and drug carrier capability of the formed micelles was examined. The results gained through fluorescence spectroscopy, transmission electron microscopy and nuclear magnetic resonance spectroscopy revealed that both polypeptide graft copolymer and its mixture with polypeptide block copolymer can self-assemble to form polymeric micelles in aqueous media. The molecular structure of the graft copolymer and blending the graft with block copolymer exert marked effects on the critical micelle concentration and the shape of formed micelles. It was found that the hydrophobic inner core of the micelles formed either by graft copolymer or mixture of graft and block copolymers can act as an incorporation site for the hydrophobic drugs. The drug loading content of the graft copolymer micelles tends to be larger when the content of the polypeptide segments in the copolymer increases. The results obtained from the drug-release studies showed that the drug-release rates are dependent on the chemical nature of the graft copolymer, the composition of the graft and block copolymer mixture, and also the pH value of the release media.
Keywords: Polypeptide; Micelle; Self-assembly; Drug delivery;

An insulin/lauryl sulfate complex was prepared by hydrophobic ion pairing (HIP). The physiochemical and biological properties of the HIP complex were characterized using octanol/water partition measurement, isothermal titration calorimetry (ITC), ultraviolet-circular dichroism (UV-CD) and Fourier transform infrared spectroscopy (FTIR). Sodium dodecyl sulfate (SDS) bound to the insulin in a stoichiometric manner. The formed complex exhibited lipophilicity, and its insulin retained its native structure integrity. The in vivo bioactivity of the complex insulin was evaluated in rats by monitoring the plasma glucose level after intravenous (i.v.) injection, and the glucose level was compared with that for free insulin. The pharmacodynamic study result in rats showed that the complex insulin had in vivo bioactivity comparable to free insulin.
Keywords: Hydrophobic ion pairing; Insulin complex; Protein structure; In vivo bioactivity;

Evaluation of osmotic effects on coated pellets using a mechanistic model by Mariagrazia Marucci; Gert Ragnarsson; Anders Axelsson (67-74).
The aim of this study was to develop a simple experimental methodology and to develop a mechanistic model to characterize the release mechanism from pellets developing cracks during the release process with special focus on osmotic effects. The release of remoxipride from pellets coated with an ethyl cellulose film was chosen as a case study. Dose release experiments at different bulk osmotic pressures revealed that the release process was mainly osmotically driven. The model was used to calculate the solvent permeability of the coating, 1.1 × 10−10  m2  h−1  MPa−1. The model was validated by release experiments using similar pellets having different coating thicknesses. The effective diffusion coefficient of remoxipride in the coating was also calculated and found to be 1.7 × 10−10  m2  h−1. A series of experiments was performed in which the osmotic pressure of the receiving solution was changed during the experiment. From the results of these experiments, the area of the cracks in the film, formed by the hydrostatic pressure built up inside the pellets, was estimated to be 3.5 × 10−5  m2/m2 coating. It could also be deduced that the solvent permeability of the coating film was affected by swelling in the same way at different osmotic pressures.
Keywords: Release mechanism; Modelling; Osmotic pumping; Diffusion; Pellets; Ethyl cellulose;

Polymer: Bioceramic composites optimization by tetracycline addition by André L. Pataro; Michele F. Oliveira; Karina I.R. Teixeira; Regina M.M. Turchetti-Maia; Miriam T.P. Lopes; Francisco H.L. Wykrota; Rubén D. Sinisterra; Maria E. Cortés (75-81).
The aim of this study was to evaluate the biocompatibility of composites of poly-lactic acid polymer (PLA) and copolymer of lactic and glycolic acid (PLGA), dispersed in a bioceramic matrix, Osteosynt® (BC), to which tetracycline (TC) was added. The in vitro test used direct contact test (ASTM F-813) and elution test (USP-XXIII, ISO 10993-5), and in vivo evaluation was performed after subcutaneous implantation in outbread Swiss mice. The 0.01% (w/w) TC addition did not affect composite cytotoxicity in vitro. The macroscopic and histologic evaluation in vivo after 1, 7, 13, 21, 28 and 56 days showed an initial intense infiltrate of inflammatory cells for most of the groups. The tissue showed normal pattern after 21 days for all the groups. TC addition exhibited significantly larger reduction of inflammation signs (Mann–Whitney test, p  < 0.05) in the critical period of the resolution of the inflammatory process. Angiogenesis, cellular adsorption and fibrous deposit were observed on SEM evaluation. In conclusion, TC addition optimized composites polymer/bioceramic biocompatibility, contributing to anti-inflammatory response during the early phases of the wound healing process.
Keywords: Tetracycline; Bioceramic; Polymer; Composite; Biocompatibility;

Effect of physical properties of troglitazone crystal on the molecular interaction with PVP during heating by Susumu Hasegawa; Naho Furuyama; Shuichi Yada; Takeshi Hamaura; Akira Kusai; Etsuo Yonemochi; Katsuhide Terada (82-89).
This study examined the effect of physical properties of troglitazone drug substance on the molecular interaction with polyvinylpyrrolidone K30 (PVP) during preparation by a closed melting method. Milling was conducted using impact and jet mills to change the physical properties of troglitazone, such as particle size, specific surface area, surface free energy and acidic–basic parameters. Solid dispersions (SDs) prepared from milled troglitazone, irrespective of milling method, showed almost 100% dissolution when not less than 7.5% of water was added during heating. SDs prepared from unmilled troglitazone showed almost 100% dissolution when not less than 12.8% of water was added during heating. Physical mixture (PM) containing unmilled troglitazone must be heated above at least 50 °C higher than the glass transition temperature (T g) of PVP to obtain an SD showing 100% dissolution, while PMs containing milled troglitazone could be heated above only 20 °C higher than the T g of PVP to obtain an SD showing 100% dissolution. The melting points of troglitazone in PMs containing milled troglitazone, irrespective of milling method, were lower than those in PMs containing unmilled troglitazone. These results indicated that specific interaction could occur more easily during heating between milled troglitazone and PVP during preparation by a closed melting method. In addition, Fourier transform infrared study indicated that hydrogen bonding could occur between the N–H of troglitazone and the C=O of PVP.
Keywords: Troglitazone; PVP; Solid dispersion; Physical property; Interaction;

Novel pharmaceutical composition of bradykinin potentiating penta peptide with β-cyclodextrin: Physical–chemical characterization and anti-hypertensive evaluation by Ângelo M.L. Denadai; Danielle Ianzer; Antônio Flávio de C. Alcântara; Marcelo M. Santoro; Cynthia F.F. Santos; Ivana Silva Lula; Antônio C.M. de Camargo; Adelaide Faljoni-Alario; Robson A.S. dos Santos; Rubén D. Sinisterra (90-98).
This work describes chemical properties and anti-hypertensive activity of an oral pharmaceutical formulation obtained from the complexation of β-cyclodextrin (β-CD) with bradykinin potentiating penta peptide (BPP-5a) founded in the Bothrops jararaca poison. Physical chemistry characterizations were recorded in order to investigate the intermolecular interactions between species in complex. Circular dichroism data indicated conformational changes of BPP-5a upon complexation with β-CD. ROESY and theoretical calculations showed a selective approximation of triptophan moiety into cavity of β-CD. Isothermal titration calorimetry data indicated an exothermic formation of the complex, which is accomplished by reduction of entropy. The anti-hypertensive activity of the BPP-5a/β-CD complex has been evaluated in spontaneous hypertensive rats, showing better results than pure BPP-5a.
Keywords: Bothrops jararaca; Bradykinin potentiating peptides; ACE inhibitors; Anti-hypertensive activity; β-Cyclodextrin;

Development and evaluation of a novel dry-coated tablet technology for pellets as a substitute for the conventional encapsulation technology by Masaki Ando; Sayaka Kojima; Yuichi Ozeki; Yukiharu Nakayama; Toshitaka Nabeshima (99-107).
Pellet formulations as represented by multiparticulate systems are often contained in hard capsules. We examined the use of a different approach to the making of compressed tablets containing pellets, OSDRC-technology. OSDRC-technology employs a double-structure punch (center punch and outer punch) allowing for dry-coated tablets to be assembled in a single run. We examined the effects of the thickness of the outer punch, formability of pellets, and diameter of tablets on pellet filling. The results revealed that thinner outer punches are not always better for filling small tablets with large amounts of pellets. We considered that this was because the core pellets spread in a cone shape within the formulating tablets at filling, requiring a thickness of the outer punch and a particle density of the diluents at which pellets would not exude from the formulating tablets. It was suggested that the formability of core pellets affects the maximum number of layers of pellets, and higher formability would yield better results. However, we found that pellets with poor formability (tensile strength of ≦2 kPa) could be used in tablets. For the tablets, the larger the diameter, the greater the maximum number of layers. We considered this to be due to the friction between the pellets and punch wall. We concluded that OSDRC-technology could be applied to capsule-like forms containing pellets ≧50 wt% through an unconventional approach.
Keywords: One-step dry-coated tablets; Dry-coated tablets; Compression-coated tablets; Capsule; Formulation;

Influence of membrane–solvent–solute interactions on solute permeation in model membranes by Monica Dias; Jonathan Hadgraft; Majella E. Lane (108-114).
The interaction of the components of topical formulations with the skin is an important consideration for effective drug delivery and efficacy. The relative importance of solubility parameters and other solvent properties on membrane diffusion processes has not been fully elucidated in the literature. In this paper, the effect of different vehicles on the permeation of caffeine, salicylic acid and benzoic acid through silicone membranes was evaluated. Polydimethylsiloxane membranes were used as model membranes for comparing the release characteristics of saturated solutions of model permeants because of their homogeneity and uniformity. Log P (octanol–water partition coefficient) and solubility parameter values were calculated for the compounds under study. In vitro diffusion studies indicated that the permeation profiles of all solutes showed a similar pattern. The permeation rates of benzoic acid and salicylic acid through silicone membrane from saturated solutions were higher than those for caffeine reflecting the more lipophilic nature of these compounds in comparison with caffeine. Solvent uptake studies confirmed that the vehicles that were highly sorbed by the membrane altered its properties and hence the flux. Vehicles that were not sorbed by the membrane showed similar steady-state fluxes for the model drugs. This suggests that the diffusion process is mainly influenced by the interactions between the vehicles and the membrane. Solubility parameter alone cannot explain the interactions between the membrane and the vehicles in all cases. Rather, it is likely that membrane flux reflects a combination of different solvent and solute characteristics, such as size, shape and charge distribution.
Keywords: Solubility parameter; Vehicle; Dermal; Transdermal; Permeation; Flux;

Human oral drugs absorption is correlated to their in vitro uptake by brush border membrane vesicles by Nathalie Oulianova; Deping Cheng; Norman Huebert; Yanmin Chen (115-121).
Brush border membrane vesicles (BBMV) were prepared from the rabbit small intestine for testing drug absorption potency through the enterocyte's apical membrane, which is an important compartment for drug oral absorption. Some modifications have been made to the traditional vesicle assay for adapting it to the 96-well plate format. The accumulation of 23 reference drugs was measured, and the data showed a good correlation with human oral absorption with a correlation coefficient R  = 0.853 (P  < 0.001), with the exception of a few false positive results. As the measured drug absorption may contain a membrane/protein binding component as well as drug uptake into vesicles, these two fractions can be discriminated by changing extravesicular osmolarity using different mannitol concentrations. This model can be applied for evaluating drug absorption rate/mechanisms, and helping drug selection in early drug research and development.
Keywords: Absorption; Transport; BBMV; In vivoin vitro correlation;

Solid dispersions of itraconazole and enteric polymers made by ultra-rapid freezing by Kirk A. Overhoff; Alejandro Moreno; Dave A. Miller; Keith P. Johnston; Robert O. Williams (122-132).
The primary objective of the study is to investigate the influence of composition parameters including drug:polymer ratio and polymer type, and particle structure of enteric solid dispersions on the release of ITZ under sink and supersaturated dissolution conditions. Modulated differential scanning calorimetry (MDSC) was utilized to define the level of ITZ miscibility with each polymer. The compositions were completely miscible at 60% ITZ for both polymers and as high as 70% in HP-55. High potency composition glass transition temperatures (T g) correlated with predicted T g's from the Gordon–Taylor equation, however, recrystallization exotherms revealed pure amorphous regions indicating that phase separation occurred during particle formation. Furthermore, in vitro studies including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), surface area analysis (BET), and dissolution were performed to determine differences between low potency (completely miscible) and high potency (partially miscible) compositions. Dissolution studies on low potency ITZ compositions revealed that miscibility plays an active role in ITZ release under sink conditions, and square root diffusion through the enteric polymer is observed. Supersaturated dissolution profiles revealed high potency compositions had maximum saturation levels (C/ C e q max ) between 10.6- and 8-times equilibrium solubility, but had higher cumulative extents of supersaturation, compared to low potency compositions which had C/ C e q max values of 15–19.6. However, these low potency compositions rapidly precipitated leading to significantly lower AUCs (p  < 0.05). The change in the miscibility of the solid dispersion had a pronounced effect of drug release (sink) while differences in potency influenced supersaturated dissolution profiles.
Keywords: Particle engineering; Amorphous; Supersaturation; Nanoparticle; Enteric polymer; Dissolution model;

Molecular mechanism involved in the transport of a prodrug dopamine glycosyl conjugate by A. Dalpiaz; R. Filosa; P. de Caprariis; G. Conte; F. Bortolotti; C. Biondi; A. Scatturin; P.D. Prasad; B. Pavan (133-139).
We have previously demonstrated that dopamine conjugation to glucose allows it to induce therapeutic effects against Parkinson's disease after intravenous administration. In this paper we demonstrate that, unlike dopamine, the prodrug glu-dopamine is a transportable substrate of glucose transporters. Towards this, the effect of glucose-conjugation on the affinity and uptake of dopamine have been assessed in vitro, using human retinal pigment epithelium (HRPE) cells. Glucose transporter-mediated uptake was measured using [3H]3-O-methylglucose ([3H]3-O-MG) as the tracer. The uptake was found to be rapid and hyperbolically related to its concentrations (K t  = 7.8 ± 1.2 mM and V max  = 54 ± 2 nmol/min mg protein). Inhibition experiments showed that dopamine was able to interact with glucose carriers only when conjugated to glucose (IC50  = 2.6 ± 0.6 mM). HPLC analysis of HRPE cell extracts showed that both dopamine and the prodrug permeate the cell, but only the uptake of the prodrug is inhibitable by glucose. This confirms that glucose transporters mediate the transport of the prodrug glu-dopamine, but not of dopamine. HRPE cells is therefore proposed as a promising model for in vitro studies involving the glucose transporter-mediated transport of drugs and their conjugates.
Keywords: Dopamine; Drug targeting; Glucose; Glucose transporters; HRPE cells;

Towards a correlation between drug properties and in vitro transdermal flux variability by Yakov Frum; Gul M. Khan; Jan Sefcik; Jennifer Rouse; Gillian M. Eccleston; Victor M. Meidan (140-147).
Over recent years, there has been growing evidence that the permeability coefficient variability describing any specific transdermal drug delivery system is not always normally distributed. However, since different researchers have used different test compounds, methodologies and skin types, it has been difficult to identify any general correlation between drug properties and flux variability. The aim of the present study was to investigate whether there was a relationship between these two variables. To this end, six different compounds (sucrose, adenosine, aldosterone, corticosterone, oestradiol and testosterone) exhibiting a range of partition coefficients but relatively similar molecular weights were screened by taking multiple replicate measurements of their permeation profiles as they penetrated across porcine skin in vitro. It was found that for relatively hydrophilic solutes (log  P o/w  ≤ ∼2.5), physicochemical properties that facilitated slow transdermal flux were associated with more positively skewed permeability coefficient distributions while rapid flux was associated with more symmetric distributions. However, no correlation could be found between molecular properties and the extent of statistical fit to either the normal or log-normal distribution.
Keywords: Transdermal; Permeability coefficient; Variability; Normal distribution; Log-normal distribution;

Effect of preparation method on compactability of paracetamol granules and agglomerates by Frauke Fichtner; Åke C. Rasmuson; Eva M. Ålander; Göran Alderborn (148-158).
The objective of this study was to investigate the effect of fracture strength of paracetamol particles on their compactability. For this purpose two series of paracetamol particles were prepared by crystal agglomeration and by granulation using different solvents. A free flowing particle size fraction of all types of particles was characterized with respect to their shape, degree of agglomeration and single fracture strength. The powders were compressed to tablets and the compression mechanism of the particles and the evolution in tablet micro-structure were assessed by compression parameters derived from the Heckel and Kawakita equations and by a tablet permeabililty coefficient. Tablet tensile strength and porosity were determined. The degree of deformation and fragmentation during compression varied between agglomerates and granules and was dependent on their failure strength. The granules varied in compactability with particle failure strength while the agglomerates showed limited variation. It is proposed that, the dominant mechanism of compression for the granules was permanent deformation while for the agglomerates it was fragmentation. It was thus found that the compression mechanism of the particles was dependent on both the degree of agglomeration and the particle failure strength.
Keywords: Wet granulation; Crystal agglomeration; Particle fracture strength; Degree of agglomeration; Tablet tensile strength;

Sustained release of hydrophobic and hydrophilic drugs from a floating dosage form by Yong-Dan Tang; Subbu S. Venkatraman; Freddy Y.C. Boey; Li-Wei Wang (159-165).
Floating dosage forms enable the sustained delivery of drugs in the gastro-intestinal tract. In this study, a type of multi-unit floating gel bead was synthesized with calcium alginate, sunflower oil, and a drug of interest through an emulsification/gelation process. The alginate beads with oil addition were able to continuously float over the medium for 24 h under constant agitation while the non-oily beads could not. Three kinds of drugs with different hydrophilicities, ibuprofen, niacinamide and metoclopramide HCl, were tested in the study. The hydrophobic drug ibuprofen was released in a sustained manner for 24 h, due to the oil partitioning. With suitable modification, the beads were able to also release the hydrophilic drugs, niacinamide and metoclopramide HCl, for a similar duration. Therefore a floating dosage form that is able to sustain release both hydrophobic and hydrophilic drugs within its extended gastric retention time has been developed.
Keywords: Gastric retentive dosage form (GRDF); Floating system; Alginate; Sustained release;

N-Trimethyl chitosan chloride (TMC) nanoparticles were prepared by ionic crosslinking of TMC with tripolyphosphate (TPP). Two model proteins with different pI values, bovine serum albumin (BSA, pI  = 4.8) and bovine hemoglobin (BHb, pI  = 6.8), were used to investigate the loading and release features of the TMC nanoparticles. TMC samples with different degrees of quaternization were synthesized to evaluate its influence on the physicochemical properties and release profiles of the nanoparticles. Sodium alginate was used to modify the TMC nanoparticles to reduce burst release. The results indicated that the TMC nanoparticles had a high loading efficiency (95%) for BSA but a low one (30%) for BHb. The particle size and zeta potential were significantly affected by the BSA concentration but not by the BHb concentration. Nanoparticles of TMC with a lower degree of quaternization showed an increase in particle size, a decrease in zeta potential and a slower drug-release profile. As for the alginate-modified nanoparticles, a smaller size and lower zeta potential were observed and the burst release of BSA was reduced. These studies demonstrated that TMC nanoparticles are potential protein carriers, and that their physicochemical properties and release profile could be optimized by means of various modifications.
Keywords: N-Trimethyl chitosan chloride; Nanoparticles; Protein delivery; In vitro release;

Modeling cytoplasmic release of encapsulated oligonucleotides from cationic liposomes by Ali M. Tamaddon; Farshad H. Shirazi; Hamid R. Moghimi (174-182).
Transfection activity of antisense oligodeoxynucleotides (ODN)-loaded cationic liposomes is mainly restricted by uptake and ODN release into cytoplasm, which is difficult to evaluate in cell culture studies. Well-designed models of cellular membranes, aim of the present study, might facilitate investigation of such processes. In this investigation, a phosphorothioate ODN was actively encapsulated in a DODAP-containing cationic liposome by ethanol injection with 73% efficiency. ODN release was determined by fluorescence dequenching of FITC-ODN upon incubation of liposomes with early endosomal (EE), late endosomal (LE) and plasma membranes (PM) models. LE provided the highest release (up to 76%) in a temperature-dependent manner. Release by EE (<16%), total PM (<11%) and PM external layer (≈0) were not temperature sensitive. These differences are attributed to lipid charge, chain mobility, critical packing parameter and cholesterol content of the models. Intracellular distribution of FITC-ODN, determined by fluorescence microscopy and flowcytometry in the presence and absence of sodium azide, confirmed that liposomes were internalized mainly via endocytosis; hence inability of our PL models to simulate such active processes. Instead, release of ODN from endosomes into cytoplasm was pH-sensitive and in good agreement with model membrane studies in terms of amount and mechanism.
Keywords: Gene delivery; Cationic liposome; Antisense oligodeoxynucleotide; Encapsulation; Model membrane; Cytoplasmic release; Cellular uptake;

In vitro evaluation of dendrimer prodrugs for oral drug delivery by Mohammad Najlah; Sally Freeman; David Attwood; Antony D’Emanuele (183-190).
Dendrimer-based prodrugs were used to enhance the transepithelial permeability of naproxen, a low solubility model drug. The stability of the dendrimer–naproxen link was assessed. Naproxen was conjugated to G0 polyamidoamine (PAMAM) dendrimers either by an amide bond or an ester bond. The stability of G0 prodrugs was evaluated in 80% human plasma and 50% rat liver homogenate. The cytotoxicity of conjugates towards Caco-2 cells was determined and the transport of the conjugates across Caco-2 monolayers (37 °C) was reported. In addition, one lauroyl chain (L) was attached to the surface group of G0 PAMAM dendrimer of the diethylene glycol ester conjugate (G0-deg-NAP) to enhance permeability. The lactic ester conjugate, G0-lact-NAP, hydrolyzed slowly in 80% human plasma and in 50% rat liver homogenate (t 1/2  = 180 min). G0-deg-NAP was hydrolyzed more rapidly in 80% human plasma (t 1/2  = 51 min) and was rapidly cleaved in 50% liver homogenate (t 1/2  = 4.7 min). The conjugates were non-toxic when exposed to Caco-2 cells for 3 h. Permeability studies showed a significant enhancement in the transport of naproxen when conjugated to dendrimers; L-G0-deg-NAP yielding the highest permeability. Dendrimer-based prodrugs with appropriate linkers have potential as carriers for the oral delivery of low solubility drugs such as naproxen.
Keywords: PAMAM dendrimers; Enzymatic stability; Transepithelial transport; Caco-2 cells; Prodrugs;

Crystallization rate of amorphous nifedipine analogues unrelated to the glass transition temperature by Tamaki Miyazaki; Sumie Yoshioka; Yukio Aso; Toru Kawanishi (191-195).
To examine the relative contributions of molecular mobility and thermodynamic factor, the relationship between glass transition temperature (T g) and the crystallization rate was examined using amorphous dihydropyridines (nifedipine (NFD), m-nifedipine (m-NFD), nitrendipine (NTR) and nilvadipine (NLV)) with differing T g values. The time required for 10% crystallization, t 90, was calculated from the time course of decreases in the heat capacity change at T g. The t 90 of NLV and NTR decreased with decreases in T g associated with water sorption. The t 90 versus T g/T plots almost overlapped for samples of differing water contents, indicating that the crystallization rate is determined by molecular mobility as indicated by T g. In contrast, differences in the crystallization rate between these four drugs cannot be explained only by molecular mobility, since the t 90 values at a given T g/T were in the order: NLV > NTR > NFD ≈  m-NFD. A lower rate was obtained for amorphous drugs with lower structural symmetry and more bulky functional groups, suggesting that these factors are also important. Furthermore, the crystallization rate of NTR in solid dispersions with poly(vinylpyrrolidone) (PVP) and hydroxypropyl methylcellulose (HPMC) decreased to a greater extent than expected from the increased T g. This also suggests that factors other than molecular mobility affect the crystallization rate.
Keywords: Crystallization; Amorphous state; Nifedipine; Glass transition; Molecular mobility; Excipients;

Noticeboard (196).