Drug delivery strategies for the treatment of Helicobacter pylori infections

Helicobacter pylori is one of the most common pathogenic bacterial infections, colonising an estimated half of all humans. It is associated with the development of serious gastroduodenal disease - including peptic ulcers, gastric lymphoma and acute chronic gastritis. Current recommended regimes are not wholly effective and patient compliance, side-effects and bacterial resistance can be problematic. Drug delivery to the site of residence in the gastric mucosa may improve efficacy of the current and emerging treatments. Gastric retentive delivery systems potentially allow increased penetration of the mucus layer and therefore increased drug concentration at the site of action. Proposed gastric retentive systems for the enhancement of local drug delivery include floating systems, expandable or swellable systems and bioadhesive systems. Generally, problems with these formulations are lack of specificity, limited to mucus turnover or failure to persist in the stomach. Gastric mucoadhesive systems are hailed as a promising technology to address this issue, penetrating the mucus layer and prolonging activity at the mucus-epithelial interface. This review appraises gastroretentive delivery strategies specifically with regard to their application as a delivery system to target Helicobacter. As drug-resistant strains emerge, the development of a vaccine to eradicate and prevent reinfection is an attractive proposition. Proposed prophylactic and therapeutic vaccines have been delivered using a number of mucosal routes using viral and non-viral vectors. The delivery form, inclusion of adjuvants, and delivery regime will influence the immune response generated. © 2005 Bentham Science Publishers Ltd.

Human drug metabolism:an introduction

Human Drug Metabolism, An Introduction, Second Edition provides an accessible introduction to the subject and will be particularly invaluable to those who already have some understanding of the life sciences. Completely revised and updated throughout, the new edition focuses only on essential chemical detail and includes patient case histories to illustrate the clinical consequences of changes in drug metabolism and its impact on patient welfare. After underlining the relationship between efficacy, toxicity and drug concentration, the book then considers how metabolizing systems operate and how they impact upon drug concentration, both under drug pressure and during inhibition. Factors affecting drug metabolism, such as genetic polymorphisms, age and diet are discussed and how metabolism can lead to toxicity is explained. The book concludes with the role of drug metabolism in the commercial development of therapeutic agents as well as the pharmacology of some illicit drugs. © 2010 John Wiley & Sons, Ltd.

A new rapidly absorbed paracetamol tablet containing sodium bicarbonate. II. Dissolution studies and in vitro/in vivo correlation

The objective of this study was to compare the in vitro dissolution profile of a new rapidly absorbed paracetamol tablet containing sodium bicarbonate (PS) with that of a conventional paracetamol tablet (P), and to relate these by deconvolution and mapping to in vivo release. The dissolution methods used include the standard procedure described in the USP monograph for paracetamol tablets, employing buffer at pH5.8 or 0.05 M HCl at stirrer speeds between 10 and 50 rpm. The mapping process was developed and implemented in Microsoft Excel® worksheets that iteratively calculated the optimal values of scale and shape factors which linked in vivo time to in vitro time. The in vitro-in vivo correlation (IVIVC) was carried out simultaneously for both formulations to produce common mapping factors. The USP method, using buffer at pH5.8, demonstrated no difference between the two products. However, using an acidic medium the rate of dissolution of P but not of PS decreased with decreasing stirrer speed. A significant correlation (r=0.773; p<.00001) was established between in vivo release and in vitro dissolution using the profiles obtained with 0.05 M HCl and a stirrer speed of 30 rpm. The scale factor for optimal simultaneous IVIVC in the fasting state was 2.54 and the shape factor was 0.16; corresponding values for mapping in the fed state were 3.37 and 0.13 (implying a larger in vitro-in vivo time difference but reduced shape difference in the fed state). The current IVIVC explains, in part, the observed in vivo variability of the two products. The approach to mapping may also be extended to different batches of these products, to predict the impact of any changes of in vitro dissolution on in vivo release and plasma drug concentration-time profiles.

Azidoprofen as a soft anti-flammatory agent for the topical treatment of Psoriasis

Azidoprofen {2-(4-azidophenyl)propionic acid; AZP}, an azido-substituted arylalkanoic acid, was investigated as a model soft drug candidate for a potential topical non-steroidal anti-inflammatory agent (NSAIA). Reversed-phase high performance liquid chromatography (HPLC) methods were developed for the assay of AZP, a series of ester analogues and their· degradation products. 1H-NMR spectroscopy was also employed as an analytical method in selected cases. Reduction of the azido-group to the corresponding amine has been proposed as a potential detoxification mechanism for compounds bearing this substituent. An in vitro assay to measure the susceptibility of azides towards reduction was developed using dithiothreitol as a model reducing agent. The rate of reduction of AZP was found to be base-dependent, hence supporting the postulated mechanism of thiol-mediated reduction via nucleophilic attack by the thiolate anion. Prodrugs may enhance topical bioavailability through the manipulation of physico-chemical properties of the parent drug. A series of ester derivatives of AZP were investigated for their susceptibility to chemical and enzymatic hydrolysis, which regenerates the parent acid. Use of alcoholic cosolvents with differing alkyl functions to that of the ester resulted in transesterification reactions, which were found to be enzyme-mediated. The skin penetration of AZP was assessed using an in vitro hairless mouse skin model, and silastic membrane in some cases. The rate of permeation of AZP was found to be a similar magnitude to that of the well established NSAIA ibuprofen. Penetration rates were dependent on the vehicle pH and drug concentration when solutions were employed. In contrast, flux was independent of pH when suspension formulations were used. Pretreatment of the skin with various enhancer regimes, including oleic acid and azone in propylene glycol, promoted the penetration of AZP. An intense IR absorption due to the azide group serves as a highly diagnostic marker, enabling azido compounds to be detected in the outer layers of the· stratum corneum following their application to skin, using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). This novel application enabled a non-invasive examination of the percutaneous penetration enhancement of a model azido compound in vivo in man, in the presence of the enhancer oleic acid.

A novel concentration dependent amino acid ion pair strategy to mediate drug permeation using indomethacin as a model insoluble drug

Assessment of oral drug bioavailability is an important parameter for new chemical entities (NCEs) in drug development cycle. After evaluating the pharmacological response of these new molecules, the following critical stage is to investigate their in vitro permeability. Despite the great success achieved by prodrugs, covalent linking the drug molecule with a hydrophobic moiety might result in a new entity that might be toxic or ineffective. Therefore, an alternative that would improve the drug uptake without affecting the efficacy of the drug molecule would be advantageous. The aim of the current study is to investigate the effect of ion-pairing on the permeability profile of a model drug: indomethacin (IND) to understand the mechanism behind the permeability improvement across Caco-2 monolayers. Arginine and lysine formed ion-pairs with IND at various molar ratios 1:1, 1:2, 1:4 and 1:8 as reflected by the double reciprocal graphs. The partitioning capacities of the IND were evaluated using octanol/water partitioning studies and the apparent permeabilities (P app) were measured across Caco-2 monolayers for the different formulations. Partitioning studies reflected the high hydrophobicity of IND (Log P = 3) which dropped upon increasing the concentrations of arginine/lysine in the ion pairs. Nevertheless, the prepared ion pairs improved IND permeability especially after 60 min of the start of the experiment. Coupling partitioning and permeability results suggest a decrease in the passive transcellular uptake due to the drop in IND portioning capacities and a possible involvement of active carriers. Future work will investigate which transport gene might be involved in the absorption of the ion paired formulations using molecular biology technologies. © 2014 Elsevier B.V. All rights reserved.

High-strength resorbable brushite bone cement with controlled drug-releasing capabilities

Brushite cements differ from apatite-forming compositions by consuming a lot of water in their setting reaction whereas apatite-forming cements consume little or no water at all. Only such cement systems that consume water during setting can theoretically produce near-zero porosity ceramics. This study aimed to produce such a brushite ceramic and investigated whether near elimination of porosity would prevent a burst release profile of incorporated antibiotics that is common to prior calcium phosphate cement delivery matrices. Through adjustment of the powder technological properties of the powder reactants, that is particle size and particle size distribution, and by adjusting citric acid concentration of the liquid phase to 800 mM, a relative porosity of as low as 11% of the brushite cement matrix could be achieved (a 60% reduction compared to previous studies), resulting in a wet unprecompacted compressive strength of 52 MPa (representing a more than 100% increase to previously reported results) with a workable setting time of 4.5 min of the cement paste. Up to 2 wt.% of vancomycin and ciprofloxacin could be incorporated into the cement system without loss of wet compressive strength. It was found that drug release rates could be controlled by the adjustable relative porosity of the cement system and burst release could be minimized and an almost linear release achieved, but the solubility of the antibiotic (vancomycin > ciprofloxacin) appeared also to be a crucial factor.

Interaction of peptides, peptidomimetics and other drug candidates with the DI/tripeptide transport system in intestinal epithelial cells, using the in vitro caco-2 cell culture system

An uptake system was developed using Caco-2 cell monolayers and the dipeptide, glycyl-[3H]L-proline, as a probe compound. Glycyl-[3H]L-proline uptake was via the di-/tripeptide transport system (DTS) and, exhibited concentration-, pH- and temperature-dependency. Dipeptides inhibited uptake of the probe, and the design of the system allowed competitors to be ranked against one another with respect to affinity for the transporter. The structural features required to ensure or increase interaction with the DTS were defined by studying the effect of a series of glycyl-L-proline and angiotensin-converting enzyme (ACE)-inhibitor (SQ-29852) analogues on the uptake of the probe. The SQ-29852 structure was divided into six domains (A-F) and competitors were grouped into series depending on structural variations within specific regions. Domain A was found to prefer a hydrophobic function, such as a phenyl group, and was intolerant to positive charges and H+ -acceptors and donors. SQ-29852 analogues were more tolerant of substitutions in the C domain, compared to glycyl-L-proline analogues, suggesting that interactions along the length of the SQ-29852 molecule may override the effects of substitutions in the C domain. SQ-29852 analogues showed a preference for a positive function, such as an amine group in this region, but dipeptide structures favoured an uncharged substitution. Lipophilic substituents in domain D increased affinity of SQ-29852 analogues with the DTS. A similar effect was observed for ACE-NEP inhibitor analogues. Domain E, corresponding to the carboxyl group was found to be tolerant of esterification for SQ-29852 analogues but not for dipeptides. Structural features which may increase interaction for one series of compounds, may not have the same effect for another series, indicating that the presence of multiple recognition sites on a molecule may override the deleterious effect of anyone change. Modifying current, poorly absorbed peptidomimetic structures to fit the proposed hypothetical model may improve oral bioavailability by increasing affinity for the DTS. The stereochemical preference of the transporter was explored using four series of compounds (SQ-29852, lysylproline, alanylproline and alanylalanine enantiomers). The L, L stereochemistry was the preferred conformation for all four series, agreeing with previous studies. However, D, D enantiomers were shown in some cases to be substrates for the DTS, although exhibiting a lower affinity than their L, L counterparts. All the ACE-inhibitors and β-lactam antibiotics investigated, produced a degree of inhibition of the probe, and thus show some affinity for the DTS. This contrasts with previous reports that found several ACE inhibitors to be absorbed via a passive process, thus suggesting that compounds are capable of binding to the transporter site and inhibiting the probe without being translocated into the cell. This was also shown to be the case for oligodeoxynucleotide conjugated to a lipophilic group (vitamin E), and highlights the possibility that other orally administered drug candidates may exert non-specific effects on the DTS and possibly have a nutritional impact. Molecular modelling of selected ACE-NEP inhibitors revealed that the three carbonyl functions can be oriented in a similar direction, and this conformation was found to exist in a local energy-minimised state, indicating that the carbonyls may possibly be involved in hydrogen-bond formation with the binding site of the DTS.

Novel biodegradable fibres for applications in tissue engineering and drug delivery

The preparation and characterisation of novel biodegradable polymer fibres for application in tissue engineering and drug delivery are reported. Poly(e-caprolactone) (PCL) fibres were produced by wet spinning from solutions in acetone under low shear (gravity flow) conditions. The tensile strength and stiffness of as-spun fibres were highly dependent on the concentration of the spinning solution. Use of a 6% w/v solution resulted in fibres having strength and stiffness of 1.8 MPa and 0.01 GPa respectively, whereas these values increased to 9.9 MPa and 0.1 GPa when fibres were produced from 20% w/v solutions. Cold drawing to an extension of 500% resulted in further increases in fibre strength (up to 50 MPa) and stiffness (0.3 GPa). Hot drawing to 500% further increased the fibre strength (up to 81 MPa) and stiffness (0.5 GPa). The surface morphology of as-spun fibres was modified, to yield a directional grooved pattern by drying in contact with a mandrel having a machined topography characterised by a peak-peak separation of 91 mm and a peak height of 30 mm. Differential scanning calorimetery (DSC) analysis of as-spun fibres revealed the characteristic melting point of PCL at around 58°C and a % crystallinity of approximately 60%. The biocompatibility of as-spun fibres was assessed using cell culture. The number of attached 3T3 Swiss mouse fibroblasts, C2C12 mouse myoblasts and human umbilical vein endothelial cells (HUVECs) on as-spun, 500% cold drawn, and gelatin coated PCL fibres were observed. The results showed that the fibres promoted cell proliferation for 9 days in cell culture and was slightly lower than on tissue culture plastic. The morphology of all cell lines was assessed on the various PCL fibres using scanning electron microscopy. The cell function of HUVECs growing on the as-spun PCL fibres was evaluated. The ability HUVECs to induce an immune response when stimulated with lipopolysaccaride (LPS) and thereby to increase the amount of cell surface receptors was assessed by flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR). The results showed that PCL fibres did not inhibit this function compared to TCP. As-spun PCL fibres were loaded with 1 % ovine albumin (OVA) powder, 1% OVA nanoparticles and 5% OVA nanoparticles by weight and the protein release was assessed in vitro. PCL fibres loaded with 1 % OVA powder released 70%, 1% OVA nanoparticle released 60% and the 5% OVA nanoparticle released 25% of their protein content over 28 days. These release figures did not alter when the fibres were subjected to lipase enzymatic degradation. The OVA released was examined for structural integrity by SDS-PAGE. This showed that the protein molecular weight was not altered after incorporation into the fibres. The bioactivity of progesterone was assessed following incorporation into PCL fibres. Results showed that the progesterone released had a pronounced effect on MCF-7 breast epithelial cells, inhibiting their proliferation. The PCL fibres display high fibre compliance, a potential for controlling the fibre surface architecture to promote contact guidance effects, favorable proliferation rate of fibroblasts, myoblasts and HUVECs and the ability to release pharmaceuticals. These properties recommended their use for 3-D scaffold production in soft tissue engineering and the fibres could also be exploited for controlled presentation and release of biopharmaceuticals such as growth factors.

Alginates as therapeutic and drug delivery systems

Alginate is widely used as a viscosity enhancer in many different pharmaceutical formulations. The aim of this thesis is to quantitatively describe the functions of this polyelectrolyte in pharmaceutical systems. To do this the techniques used were Viscometry, Light Scattering, Continuous and Oscillatory Shear Rheometry, Numerical Analysis and Diffusion. Molecular characterization of the Alginate was carried out using Viscometry and Light Scattering to determine the molecular weight, the radius of gyration, the second virial coefficient and the Kuhn statistical segment length. The results showed good agreement with similar parameters obtained in previous studies. By blending Alginate with other polyelectrolytes, Xanthan Gum and 'Carbopol', in various proportions and with various methods of low and high shear preparation, a very wide range of dynamic rheological properties was found. Using oscillatory testing, the parameters often varied over several decades of magnitude. It was shown that the determination of the viscous and elastic components is particularly useful in describing the rheological 'profiles' of suspending agent blends and provides a step towards the non-empirical formulation of pharmaceutical disperse systems. Using numerical analysis of equations describing planar diffusion, it was shown that the analysis of drug release profiles alone does not provide unambiguous information about the mechanism of rate control. These principles were applied to the diffusion of Ibuprofen in Calcium Alginate gels. For diffusion in such non-Newtonian systems, emphasis was placed on the use of the elastic as well as the viscous component of viscoelasticity. It was found that the diffusion coefficients were relatively unaffected by increases in polymer concentration up to 5 per cent, yet the elasticities measured by oscillatory shear rheometry were increased. This was interpreted in the light of several theories of diffusion in gels.

Amino acid, peptide and drug transport across monolayers of human intestinal (CAC0-2) cells in vitro

The properties of Caco-2 monolayers were compared on aluminium oxide and nitrocellulose permeable-supports. On nitrocellulose, Caco-2 cells displayed a higher rate of taurocholic acid transport than those cultured on aluminium oxide inserts. In addition, Caco-2 cells grown on these two inserts were not comparable with respect to cell morphology, cell numbers and transepithelial electrical resistance. The low adsorption potential of the aluminium oxide inserts, particularly for high molecular weight or lipophilic ligands, offers a distinct advantage over nitrocellulose inserts for drug transport studies. The carrier-mediated uptake and transport of the imino acid (L-proline) and the acidic amino acids (L-aspartate and L-glutamate) have been studied. At pH7.4, L-proline uptake is mediated via an A-system carrier. Elevated uptake and transport under acidic conditions occurs by activation of a distinct carrier population. Acidic amino acid transport is mediated via a X-AG system. The flux of baclofen, CGP40116 andCGP40117 across Caco-2 monolayers was described by passive transport. The transport of three peptides, thyrotrophin-releasing hormone, SQ29852 and cyclosporin were investigated. Thyrotrophin-releasing hormone transport acrossCaco-2 monolayers was characterised by a minor saturable (carrier-mediated,approximately 25%) pathway, superimposed onto a major non-saturable (diffusional)pathway. SQ29852 uptake into Caco-2 monolayers is described by a major saturable mechanism (Km = 0.91 mM) superimposed onto a minor passive component.However, the initial-rate of SQ29852 transport is consistent with a passive transepithelial transport mechanism. These data highlight the possibility that itsbasolateral efflux is severely retarded such that the passive paracellular transportdictates the overall transepithelial transport characteristics. In addition, modelsuitable for investigating the transepithelial transport of cyclosporin A has been developed. A modification of the conventional Caco-2 model has been developed which has a calcium-free Ap donor-solution and a Bl receiver-solution containing the minimumcalcium concentration required to maintain monolayer integrity (100 μM). The influence of calcium and magnesium on the absorption of [14C]pamidronate was evaluated by comparing its transport across the conventional and minimum calciumCaco-2 models. Ap calcium and magnesium ions retard the Ap-to-Bl flux of pamidronate across Caco-2 monolayers. The effect of self-emulsifying oleic acid-Tween 80 formulations on Caco-2monolayer integrity has been investigated. Oleic acid-Tween 80 (1 0:1) formulations produced a dose-dependent disruption of Caco-2 monolayer integrity. This disruption was related to the oleic acid content of the formulation.

Strategies for local drug delivery targeting the oesophagus

Localised, targeted drug delivery to the oesophagus offers the potential for more effective delivery and reduced drug dosages, coupled with increased patient compliance. This thesis considers bioadhesive liquids, orally retained tablets and films as well as chewable dosage forms as drug delivery systems to target the oesophagus. Miconazole nitrate was used as a model antifungal agent. Chitosan and xanthan gum hydrogels were evaluated as viscous polymer viables with the in vitro retention, drug release and minimum inhibitory concentration values of the formulations measured. Xanthan showed prolonged retention on the oesophageal surface in vitro yet chitosan reduced the MIC value; both polymers offer potential for local targeting to the oesophagus. Cellulose derivatives were investigated within orally retained dosage forms. Both drug and polymer dissolution rates were measured to investigate the drug release mechanism and to develop a formulation with concomitant drug and polymer release to target the oesophagus with solubilised drug within a viscous media. Several in vitro dissolution methods were evaluated to measure drug release from chewable dosage forms with both drug and polymer dissolution quantified to investigate the effects of dissolution apparatus on drug release. The results from this thesis show that a range of drug delivery strategies that can be used to target drug to the oesophagus. The composition of these formulations as well as the methodology used within the development are crucial to best understand the formulation and predict its performance in vivo.

Precipitation casting of drug-loaded microporous PCL matrices:incorporation of progesterone by co-dissolution

Microporous, poly(ε-caprolactone) (PCL) matrices were loaded with progesterone by precipitation casting using co-solutions of PCL and progesterone in acetone. Progesterone loadings up to 32% w/w were readily achieved by increasing the drug content of the starting PCL solution. The kinetics of steroid release in PBS at 37°C over 10 days could be described effectively by a diffusional release model although the Korsmeyer-Peppas model indicated the involvement of multiple release phenomena. The diffusion rate constant (D) increased from 8 to 24 μg/mg matrix/day0.5 as the drug loading increased from 3.6 to 12.4% w/w. A total cumulative release of 75%-95% indicates the high efficiency of steroid delivery. Increasing the matrix density from 0.22 to 0.39 g/cm3, by increasing the starting PCL solution concentration, was less effective in changing drug release kinetics. Retention of anti-proliferative activity of released steroid was confirmed using cultures of breast cancer epithelial (MCF-7) cells. Progesterone released from PCL matrices into PBS at 37°C over 14 days retarded the growth of MCF-7 cells by a factor of at least 3.5 compared with progesterone-free controls. These findings recommend further investigation of precipitation-cast PCL matrices for delivery of bioactive molecules such as anti-proliferative agents from implanted, inserted or topical devices.

On the drug adsorption capacity of SBA-15 obtained from various detemplation protocols

The effect of the mild detemplation method, based on Fenton chemistry (with and without previous solvent extraction), and calcination was evaluated by the drug uptake capacity of SBA-15 materials. A number of characterization techniques were applied for evaluation and comparison of the materials properties such as TGA, CNH, N2 physisorption and 29Si NMR. The mild Fenton detemplation method rendered a nearly pristine SBA-15 without structural shrinkage, low residual template, improved surface area, pore volume and silanol concentration. The drug (ibuprofen) adsorption experiments were carried out by solution immersion in powdery form. The mild detemplated samples experienced an enhanced uptake that could be explained by the enhanced density of silanols (mmol/g), originated from the absence of calcination in the Fenton approaches. © 2014 Elsevier B.V.