International Journal of Pharmaceutics (v.207, #1-2)
Combination of molecular modeling and quantitative structure–activity relationship analysis in the study of antimycobacterial activity of pyridine derivatives by Věra Klimešová; Karel Palát; Karel Waisser; Jiřı́ Klimeš (1-6).
A set of 4-benzylsulfanyl derivatives of pyridine-2-carbonitriles and pyridine-2-carbothioamides, previously tested for their antimycobacterial activity, were analysed by quantitative structure–activity relationship (QSAR) techniques, using some physicochemical and quantum–chemical parameters. The resulting QSAR revealed that the activity increases with electron withdrawing substituents in the benzyl moiety of studied compounds. HOMO orbitals can play an important role in the description of the mechanism of interactions at the molecular level. Additionally, the results of multiple linear regression indicate the differences between Mycobacterium tuberculosis and M. avium. The hydrophobicity of studied compounds is important for activity against M. avium.
Keywords: 4-(benzylsulfanyl)pyridine-2-carbonitrile; 4-(benzylsulfanyl)pyridine-2-carbothioamide; Antimycobacterial activity; Quantum–chemical calculations; Structure–activity relationships;
In vitro release of caffeine from concentrated W/O emulsions: effect of formulation parameters by Pascale Clément; Cécile Laugel; Jean-Paul Marty (7-20).
Concentrated water in oil emulsions have been obtained with four different emulsifiers to study the effect of formulation parameters on the in vitro release of caffeine. The in vitro release was studied on polysulfone membranes. Among the four emulsifiers, only one gave a statistically higher release of caffeine after 15 h (at a fixed percentage of dispersed phase). The concentration of the emulsifier does not have a significant effect on the release of caffeine. In contrast, diffusion of caffeine from concentrated W/O emulsions has been found to be highly dependent on the internal phase volume. The flux of caffeine increases with the percentage internal water phase. The droplet diameter decreases and the apparent viscosity increases with the percentage of the dispersed phase. And, the shape of the droplets goes from spherical to polyhedral as the percentage dispersed phase is increased. However, the flux could be correlated neither with the apparent viscosity nor with the droplet diameter at a fixed percentage of the dispersed phase. Results suggest that the shape factor may have an influence on the release of caffeine from concentrated emulsions. All the release profiles followed a zero-order kinetic.
Keywords: W/O Concentrated emulsions; Membrane diffusion; Controlled release; Formulation effects; Caffeine;
A comparison of the permeation enhancement potential of simple bile salt and mixed bile salt:fatty acid micellar systems using the CaCo-2 cell culture model by C.M Meaney; C.M O'Driscoll (21-30).
The aim of this study was to compare the permeation enhancing potential and toxicity of simple bile salt and bile salt:fatty acid mixed micellar systems using the CaCo-2 cell culture model. The effects of micellar systems of sodium cholate, (NaC), and sodium taurocholate, (NaTC), on the permeability of the hydrophilic markers, mannitol (182) and polyethylene glycols (PEGS) 900 and 4000, were assessed. Simple micelle systems of the unconjugated bile salt, NaC, caused greater enhancement of the hydrophilic markers than the conjugated bile salt, NaTC. In the case of NaC systems the enhancement was coincident with excess membrane disruption and toxicity as indicated by altered TEERs, TEMs, MTT values, and, the lack of recovery following removal of the enhancer. In contrast, the NaTC systems were less toxic, and, in the simple micelle form the likely mechanism of enhancement of the hydrophilic markers is via a transient effect on the tight junctions. Formation of mixed micellar systems with linoleic acid (LA) accentuated the toxic effects of NaC. In comparison, NaTC:LA mixed micelles showed superior permeability enhancement versus simple micelles without increasing membrane toxicity. The mechanism of enhancement of NaTC:LA appears more complex and involves a possible combination effect on both the paracellular and transcellular routes.
Keywords: CaCo-2; Sodium cholate; Sodium taurocholate; Linoleic acid; Permeability enhancement; Micellar systems;
The selection of non-steroidal anti-inflammatory agents for dermal delivery by Jonathan Hadgraft; Jeanetta du Plessis; Colleen Goosen (31-37).
An analysis has been conducted to show how the penetration of a selection of non-steroidal anti-inflammatory agents (NSAIDs) through the skin may be predicted. The calculations are based on physicochemical parameters that can be predicted using commercially available software. Where available the predictions compare favourably with the literature values. The bio-effectiveness of the NSAID will be a function of both its penetration through the skin and its potency. The variation in potency has also been considered. Most NSAIDs are carboxylic acids, therefore the pK a will be an important determinant in ionisation and hence permeation. pH partition behaviour into the skin has been considered together with the relative impact of decreased permeation but increased solubility with degree of ionisation.
Keywords: Non-steroidal anti inflammatory; Skin penetration; Modelling; Transdermal delivery;
Protective effect caused by the exopolymer excreted by Pseudoalteromonas antarctica NF3 on liposomes against the action of octyl glucoside by M Cócera; O López; J.L Parra; M.E Mercadé; J Guinea; A de la Maza (39-47).
The capacity of the glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF3, to protect phosphatidylcholine (PC) liposomes against the action of octyl glucoside (OG) was studied in detail. Increasing amounts of GP assembled with liposomes resulted for the same interaction step in a linear increase in the effective surfactant to PC molar ratios (Re) and in a linear fall in the surfactant partitioning between bilayer and the aqueous phase (partition coefficients K). Thus, the higher the proportion of GP assembled with liposomes the lower the surfactant ability to alter the permeability of vesicles and the lower its affinity with these bilayer structures. In addition, increasing GP proportions resulted in a progressive increase of the free surfactant concentration (S W) needed to produce the same alterations in liposomes. The fact that S W was always lower than the surfactant critical micelle concentration indicates that the interaction was mainly ruled by the action of surfactant monomers, regardless of the amount of assembled GP.
Keywords: New antarctica bacterial species Pseudoalteromonas antarctica NF3; Exopolymer of glycoproteic character; Phosphatidylcholine liposomes; Octyl glucoside; Permeability alterations; Carboxyfluorescein release; Effective molar ratio of surfactant to phospholipid in bilayers; Surfactant partition coefficient;
The novel combination of dynamic vapour sorption gravimetric analysis and near infra-red spectroscopy as a hyphenated technique by Roy A Lane; Graham Buckton (49-56).
The novel combination of an environmental controlled gas flow microbalance (Dynamic Vapour Sorption, Surface Measurement Systems, UK) with a NIR spectrometer (Foss NIR Systems) is described. The study follows the gravimetric changes and the spectroscopic changes in the amorphous and crystalline states of lactose at 298 K. NIR spectra and gravimetric water sorption were recorded simultaneously for the same sample. Differentiation of the amorphous and crystalline states of lactose was possible from the evaluation of peak intensity and shifts in the known fingerprint regions of the NIR spectra, i.e. 1350–1510 and 1825–1975 nm which correspond to water changes, and 2075–2160 nm which tends to illustrate changes in the organic/structural backbone character. Gravimetric analysis confirmed that the amorphous lactose crystallised, as weight changes can be linked to structural changes. The combined technique maintains the high performance of the DVS microbalance for gravimetric analysis but also provides a preset, regulated and controllable environment for studies using NIR spectroscopy probes, which was previously not possible. The results obtained agree with accepted data, and therefore provide validation for the hyphenation technique. The use of the combined DVS-NIR instrument has indicated two new pieces of information, firstly the amorphous form loses some water before the crystallisation is detectable. This indicates that water desorption may precede crystallisation, rather than the other way around, and secondly, the sample has completed crystallisation before water desorption has ended.
Keywords: Near infra-red; Dynamic vapour sorption; Water sorption; Amorphous; Lactose; Crystalline;
The quantification of small degrees of disorder in lactose using solution calorimetry by Sarah E Hogan; Graham Buckton (57-64).
There is a realisation that small quantities of amorphous material can have a significant impact on the properties of crystalline solids. Consequently there is a growing interest in quantifying the amount of amorphous material that is present in “crystalline powders”. Success has been reported when using isothermal microcalorimetry and vapour sorption techniques, however, the use of solution calorimetry has largely been ignored. In this study the enthalpies of solution of mixtures of amorphous and crystalline lactose are reported concentrating on the range 0–10% w/w amorphous content. It was found that there was a possible error due to water vapour penetration into the ampoule, resulting in crystallisation of the amorphous content, however this was overcome by double sealing the ampoules with wax. Subsequently there was a good correlation between the enthalpy of solution and the amorphous content, which was not adversely affected by stirring rate used during the experiment. Over the range from 0 to 10% amorphous content, quantification of the amorphous content of an unknown would be good to ±0.5%. The effects of residual moisture retained within a sample were also investigated. Storage at 33% or 43% RH resulted in a much reduced wetting (exothermic) response compared with that seen for completely dry samples, which in turn led to a higher net enthalpy of solution.
Keywords: Amorphous quantification; Crystalline; Solution calorimetry;
Preparation and in-vitro evaluation of poly[N-vinyl-2-pyrrolidone-polyethylene glycol diacrylate]-chitosan interpolymeric pH-responsive hydrogels for oral drug delivery by K.L. Shantha; D.R.K. Harding (65-70).
Biocompatible and biodegradable pH-responsive hydrogels based on N-vinyl pyrrolidone (NVP), polyethylene glycol diacrylate (PAC) and chitosan were prepared for controlled drug delivery. These interpolymeric hydrogels were synthesized by a free radical polymerization technique using azobisisobutyronitrile (AIBN) as initiator and N,N′-methylenebisacrylamide (BIS) as crosslinker. These hydrogels were subjected to equilibrium swelling studies in enzyme-free simulated gastric and intestinal fluids (SGF and SIF). These swelling studies clearly indicated that these hydrogels were swollen more in SGF when compared to SIF. Theophylline and 5-fluorouracil (5-FU) were entrapped into these hydrogels and equilibrium-swelling studies were carried out for the drug-entrapped gels in enzyme-free SGF and SIF. The in-vitro release profiles of the drugs were established in enzyme-free SGF. More than 50% of the entrapped drugs were released in the first 2 h at gastric pH and the rest of the drug release was slower.
Keywords: pH-responsive; Interpolymeric hydrogel; Equilibrium swelling; Drug-delivery;
Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: in vitro immunosuppressive effects on rat blood and spleen lymphocytes by Katherine L Rensberger; Dean A Hoganson; Reza Mehvar (71-76).
The in vitro immunosuppressive activity of a conjugate of methylprednisolone (MP) with dextran 70 kDa (DEX-MPS) was tested using the lymphocyte proliferation assay after stimulation of lymphocytes with concanavalin A (Con-A). Blood and spleen lymphocytes, isolated from drug-free male Sprague–Dawley rats, were used in the assay. First, the optimum concentration of Con-A for stimulation of lymphocytes was determined. The inhibition of the lymphocyte proliferation was then tested in the presence of 0.25, 0.5, 1.0, 2.5, 5.0, 10, 20, and 50 nM concentrations (MP equivalent) of DEX-MPS or free MP. The maximum stimulation of lymphocytes with Con-A was observed at mitogen concentrations of 2.5 and 10 μg/ml for the spleen and blood lymphocytes, respectively. For free MP, sigmoidal relationships were observed between the effect (% inhibition of lymphocyte proliferation) and the logarithm of MP concentration. Additionally, the maximum inhibitory effect (I max) and MP concentration producing half of I max (IC50) were, respectively, 98% and 1.38 nM for the blood and 86% and 3.1 nM for the spleen lymphocytes. For MP conjugated to dextran, the response–log concentration curves were substantially shifted to the right with IC50 values of 40 and 52 nM for the blood and spleen lymphocytes, respectively. It is concluded that compared with free MP, the steroid attached to dextran has minimal immunosuppressive activity. Therefore, to be effective in vivo, DEX-MPS should release MP in the body.
Keywords: Methylprednisolone; Dextran-methylprednisolone conjugate; Immunosuppression; Lymphocyte proliferation; Splenocytes; Targeted delivery;
The utilization of surface free-energy parameters for the selection of a suitable binder in fluidized bed granulation by O Planinšek; R Pišek; A Trojak; S Srčič (77-88).
Surface free energy was determined for model substances pentoxyfilline, acyclovir, lactose and binding agents (that were used in the granulation process) hydroxypropilmethyl cellulose (HPMC) and polyvinylpyrrolidone (PVP) were determined by contact angle measurements. The methods of Wu, Good–van Oss and Della Volpe were used for solid-surface free-energy calculation. Spreading coefficients (S) were calculated and correlated with granulate properties. Granulates consisted of model drug and binding agent, and were produced in fluid bed granulator Glatt powder coater granulator GPCG1 by means of spraying the colloidal solution of binder on the model substance. Granules contained either 5% or 10% binder. Inverse granules, however, were also produced by spraying the model drug (i.e. pentoxyfilline and lactose) on the binding agent (HPMC, PVP). Particle size distribution, friability, true density, bulk density and tapped density of the granulates were determined. Although many different parameters influence the granule properties, it has been found that the interactions between the drug and the binder play a very important role. Spreading coefficients were found to be in good correlation with the friability of granulates. Positive spreading coefficient values of the binder over the model substance correlate well with the low friability of the granules containing lower amount of binder, i.e. 5%. In the group of the same binder, the spreading coefficient values decrease from pentoxyfilline over lactose to acyclovir. Friability results show that, for the system under consideration, PVP offers certain advantages over the grade of HPMC employed. The increase of the binder amount from 5 to 10% resulted in more friable granulates. Lower work of cohesion of the binder (PVP and HPMC) than the work of adhesion between binder and the model substances is considered responsible for the higher friability of the granules. The inverse granulation process, where the suspension of the model substance was sprayed over the solid binder particles, proved more efficient with HPMC than with PVP. According to the spreading coefficient results, the binder should spread over the drug. However, the kinetics of wetting appears to play an important role in the granulation process. According to these results, the conclusion was made that water wets HPMC much faster than PVP.
Keywords: Contact angle; Surface free energy; Spreading coefficient; Fluid bed granulation; Granulate properties;
Application of in vivo confocal microscopy to the objective evaluation of ocular irritation induced by surfactants by P Furrer; B Plazonnet; J.M Mayer; R Gurny (89-98).
An ocular irritation test using confocal laser scanning ophthalmoscopy has been developed in which corneal lesions subsequent to instillation of surfactants are specifically marked by fluorescein and assessed by digital image processing. The sum of the observed fluorescent corneal areas is taken into account as an endpoint of ocular irritation. Eight currently used nonionic, cationic and anionic surfactants were applied onto the cornea of rabbits and mice, four times per day during 3 days at various concentrations. Benzalkonium chloride, a cationic surfactant, at a concentration range of 0.01–0.5%, was tested in the same manner. The cornea was evaluated in vivo for ocular tolerance by confocal microscopy. In both rabbits and mice, the test revealed following irritation rankings: cationic>anionic>nonionic surfactants. Furthermore, in both animal models, the ocular damage increased with the concentration of benzalkonium. The test was sensitive enough to detect ocular microlesions at concentrations of surfactants as low as 0.01% for benzalkonium. These findings demonstrate the usefulness of confocal microscopy for the non-invasive, in situ evaluation of ocular tolerance.
Keywords: Confocal microscopy; Cornea; Draize eye test; Surfactants; Preservatives; Image analysis;
Effect of solvent on the preparation of surfactant-free poly(dl-lactide-co-glycolide) nanoparticles and norfloxacin release characteristics by Hyun-Jeong Jeon; Young-Il Jeong; Mi-Kyeong Jang; Young-Hoon Park; Jae-Woon Nah (99-108).
The surfactant-free nanoparticles of poly(dl-lactide-co-glycolide) (PLGA) were prepared by dialysis method without surfactant and physicochemical properties such as particle size and drug contents were investigated against used initial solvent. The size of PLGA nanoparticles and drug contents were significantly changed by used initial solvent. The size of PLGA nanoparticles prepared from dimethylacetamide (DMAc), dimethylformamide (DMF), and dimethylsulfoxide (DMSO) as a initial used solvent was smaller than that of acetone. Selected initial solvent used to dissolve the copolymer significantly affects the size of nanoparticles and drug contents. It was shown that PLGA nanoparticles have spherical shapes from the results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. It was thought that surfactant-free nanoparticles of PLGA entrapping norfloxacin (NFX) has nice drug loading capacity without free-drug on the surface of nanoparticles through the analysis of X-ray powder diffraction. From these results, it was showed the potential that the PLGA nanoparticles could be formed successively by dialysis method without surfactant. Release kinetics of NFX used as a model drug was governed by not only drug contents but also particle size parameter. The higher the drug contents and the larger the particle size resulted in slower the drug release.
Keywords: Poly(dl-lactide-co-glycolide); Surfactant-free nanoparticles; Used initial solvent; Dialysis method; Norfloxacin; Controlled drug release;
A new long acting ophthalmic formulation of Carteolol containing alginic acid by Odile Séchoy; Gérard Tissié; Chantal Sébastian; Florence Maurin; Jean-Yves Driot; Claude Trinquand (109-116).
Alginic acid was evaluated as a potential vehicle in ophthalmic solutions for prolonging the therapeutic effect of carteolol. This anionic vehicle was expected to slow down drug elimination by the lacrimal flow, both by undergoing in-situ gel formation and by interacting with the mucus. In vitro studies indicated that carteolol is released slowly from alginic acid formulations, suggesting an ionic interaction. The adhesive behavior of alginic acid solution was better than that of another polymer, hydroxyethylcellulose (HEC). Intraocular pressure (IOP) measurements of rabbit eyes treated with a 1% carteolol formulation with or without alginic acid showed that this polymer significantly extended the duration of the pressure-reducing effect of carteolol to 8 h. The increased ocular bioavailability of 1% carteolol in the presence of alginic acid led to an equivalent concentration in the target tissue although administration was only once a day compared with twice a day for 1% carteolol alone. The overall results of this study indicate that the alginic-acid vehicle is an excellent drug carrier, well tolerated, and could be used for the development of a long-acting ophthalmic formulation of carteolol.
Keywords: Alginic acid; Carteolol; Ophthalmic delivery; Bioavailability; Intraocular pressure;
Comments on Serger et al.'s, (1998, 1999) calorimetric stability studies by A.E. Beezer (117-118).