Dara Fitzpatrick

Micellar electrokinetic chromatography with amperometric detection and off-line solid-phase extraction for analysis of carbamate insecticides.

Six selected primary carbamate insecticides, methomyl, carbaryl, carbofuran, propoxur, isoprocarb, and promecarb, were hydrolyzed in alkaline solution, resulting in electroactive derivatives detectable at a platinum (Pt) electrode poised at +0.8 V vs Ag/AgCl (3 M NaCl). The Pt electrode was inserted into a small electrochemical cell and positioned close to the capillary outlet as an end-column detector to detect the carbamate derivatives after electrophoretic separation. Based on their predicted pK(a) values and aqueous solubilities, micellar electrokinetic chromatography (MEKC) was optimized for baseline separation of the derivatives using 20 mM borate, pH 10.2 containing 20 mM sodium dodecyl sulfate as a running buffer. When combined with solid-phase extraction (SPE) on octadecyl silica, a preconcentration factor of 100-fold achieved detection to 0.5 microM methomyl and to 0.01 microM for the remaining five pesticides, significantly below the level regulated by government agencies of most countries. The SPE-MEKC method when applied to the separation and analysis of spiked river water and soil samples, yielded results with excellent reproducibility, recovery and selectivity.

Iontophoretic and chemical enhancement of drug delivery. Part I: Across artificial membranes

This paper reports on measurements of the release characteristics of the model drug salbutamol base from a liquid crystalline vehicle across a non-rate limiting synthetic membrane. The measured passive release rates were compared with analogous behaviour: (i) when a penetration enhancer such as oleic acid was incorporated into the vehicle; (ii) when the release was iontophoretically assisted; and (iii) when the penetration enhancer and iontophoretic assistance were used simultaneously. The effects of using isotonic phosphate buffer solution as the aqueous domain of the vehicle and in the receptor were also separately assessed. The passive release from the standard system was consistent with matrix diffusion control. The addition of oleic acid indicated association of the drug with the fatty acid so that its release into an aqueous medium was significantly retarded. With buffer ions present in the vehicle the release rate increased consistent with reduced association, and when phosphate buffer was used as a receptor medium the release rate exceeded that of the standard vehicle due to an ion exchange process. The delivery of salbutamol from the fatty acid containing systems was substantially enhanced by iontophoresis and the rates were shown to be approximately proportional to the assisting currents. The data clearly indicate the iontophoretic process to be significantly less efficient in the presence of buffer ions but with the iontophoretic delivery rates being enhanced by the presence of a fatty acid.

Aspirated bile: a major host trigger modulating respiratory pathogen colonisation in cystic fibrosis patients

Chronic respiratory infections are a leading global cause of morbidity and mortality. However, the molecular triggers that cause respiratory pathogens to adopt persistent and often untreatable lifestyles during infection remain largely uncharacterised. Recently, bile aspiration caused by gastro-oesophageal reflux (GOR) has emerged as a significant complication associated with respiratory disease, and cystic fibrosis (CF) in particular. Based on our previous finding that the physiological concentrations of bile influence respiratory pathogens towards a chronic lifestyle in vitro, we investigated the impact of bile aspiration on the lung microbiome of respiratory patients. Sputum samples (n = 25) obtained from a cohort of paediatric CF patients were profiled for the presence of bile acids using high-resolution liquid chromatography–mass spectrometry (LC-MS). Pyrosequencing was performed on a set of ten DNA samples that were isolated from bile aspirating (n = 5) and non-bile aspirating (n = 5) patients. Both denaturing gradient gel electrophoresis (DGGE) and pyrosequencing revealed significantly reduced biodiversity and richness in the sputum samples from bile aspirating patients when compared with non-aspirating patients. Families and genera associated with the pervasive CF microbiome dominated aspirating patients, while bacteria associated with the healthy lung were most abundant in non-aspirating patients. Bile aspiration linked to GOR is emerging as a major host trigger of chronic bacterial infections. The markedly reduced biodiversity and increased colonisation by dominant proteobacterial CF-associated pathogens observed in the sputum of bile aspirating patients suggest that bile may play a major role in disease progression in CF and other respiratory diseases.

Principles and Applications of Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A Sound Approach for the Analysis of Compounds

The dissolution of a compound results in the introduction and generation of gas bubbles in the solvent. This formation is due to entrained gases adhered to or trapped within the particles. Furthermore, a reduction in gas solubility due to the solute results in additional bubble generation. Their presence increases the compressibility of the solvent with the added effect of reducing the velocity of sound in the solvent. This effect is monitored via the frequency change of acoustic resonances that are mechanically provoked in the solvent and are now used as an insightful analytical technique. An experimental set up was designed to study a large number of compounds as a function of time, concentration, and solvent system. This revealed the role of the various physical and chemical mechanisms in determining the observed response. It is also shown that this response is strongly dependent on the physical and chemical characteristics of the solute compound used, therefore resulting in a method for the characterization of compounds and mixtures. Additional factors such as morphology (polymorphism), particle size, and dissolution rate are shown to be key in the variation of the resulting response. A mathematical model has also been developed in parallel, which inter-relates the various processes involved in the observed response. It is anticipated that BARDS will open up a new window into transient dissolution processes and compound characterization.

Blend uniformity analysis of pharmaceutical products by Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS).

Blend uniformity analysis (BUA) is a routine and highly regulated aspect of pharmaceutical production. In most instances, it involves quantitative determination of individual components of a blend in order to ascertain the mixture ratio. This approach often entails the use of costly and sophisticated instrumentation and complex statistical methods. In this study, a new and simple qualitative blend confirmatory test is introduced based on a well known acoustic phenomenon. Several over the counter (OTC) product powder blends are analysed and it is shown that each product has a unique and highly reproducible acoustic signature. The acoustic frequency responses generated during the dissolution of the product are measured and recorded in real time. It is shown that intra-batch and inter-batch variation for each product is either insignificant or non-existent when measured in triplicate. This study demonstrates that Broadband Acoustic Resonance Dissolution Spectroscopy or BARDS can be used successfully to determine inter-batch variability, stability and uniformity of powder blends. This is just one application of a wide range of BARDS applications which are more cost effective and time efficient than current methods.

pH Dependence of the Dissolution Rate of Enteric- Coated Drug Spheres Determined by Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS)

Enteric coatings are widely used in formulations of drug delivery spheres. The coating protects an active pharmaceutical ingredient (API) from acidic conditions in the low pH environment of the stomach. The coating breaks down readily at higher pH in the lower intestine to allow absorption of the API. The thickness of the enteric coating is one of the factors that determine the release rate of the drug in the gastrointestinal tract. It is difficult to determine the loading of the drug layer and enteric coating on the core support sphere without conventional dissolution testing during and post manufacture. Broadband acoustic resonance dissolution spectroscopy (BARDS) potentially offers a new, rapid approach to characterizing enteric coatings during their manufacture. BARDS applications are based on reproducible changes in the compressibility of a solvent during dissolution, which is monitored acoustically via associated changes in the frequency of induced acoustic resonances. Two drug sphere formulations that yield characteristic and reproducible data were investigated. A steady-state acoustic lag time is associated with the disintegration of the enteric coating and drug layer in basic solution. This lag time is pH dependent and is indicative of the rate at which the coating and layers dissolve. BARDS analysis has the potential to characterize drug sphere formulations at-line in very short timescales. BARDS represents a complementary technique to conventional dissolution testing that could be used in precompliance testing for quality assurance during manufacture. BARDS data, in the future, may also be indicative of the likely performance of a formulation under USP dissolution testing.

Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) – A novel approach to investigate the wettability of pharmaceutical powder blends

The ability of broadband acoustic resonance dissolution spectroscopy (BARDS) to assess the wettability of powder blends is investigated. BARDS is a novel analytical technology developed on the basis of the change in acoustic phenomena observed when material is added into a solvent under resonance. Addition of solid material to the solvent results in the introduction of gas (air) into the solvent, changing the compressibility of the solvent system, and reducing the velocity of sound in the solvent. As a material is wetted and dissolved, the gas is released from the solvent and resonance frequency is altered. The main purpose of this work is to demonstrate the ability of BARDS to assess differences in the wetting behavior of tablet excipients (microcrystalline cellulose (MCC) and magnesium stearate (MgSt)) and a model drug (metoclopramide hydrochloride) as single component powders and multicomponent powder blends. BARDS acoustic responses showed a prolonged release of gas for the powdered blends with lubricant compared to unlubricated blends. As the elimination of gas from the solvent was assumed to follow first order elimination kinetics, a compressible gas elimination rate constant was calculated from the log plots of the gas volume profiles. The gas elimination rate constant was used as a parameter to compare the release of gas from the powder introduced to the solvent and hence the powder wetting behavior. A lower gas elimination rate constant was measured for lubricated blends compared to nonlubricated blends, suggesting the prolonged hydration of lubricated blends. Standard wetting techniques such as contact angle measurements and wetting time analysis were also used to analyze the blends and confirmed differences in wetting behavior determined by BARDS. The study results demonstrate the capability of BARDS as a rapid, analytical tool to determine the wetting behavior of the pharmaceutical powder blends and the potential of BARDS as a process analytical technology (PAT) tool.

Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS): A Rapid Test for Enteric Coating Thickness and Integrity of Controlled Release Pellet Formulations.

Graphical abstract Figure. No Caption available. Abstract There are no rapid dissolution based tests for determining coating thickness, integrity and drug concentration in controlled release pellets either during production or post‐production. The manufacture of pellets requires several coating steps depending on the formulation. The sub‐coating and enteric coating steps typically take up to six hours each followed by additional drying steps. Post production regulatory dissolution testing also takes up to six hours to determine if the batch can be released for commercial sale. The thickness of the enteric coating is a key factor that determines the release rate of the drug in the gastro‐intestinal tract. Also, the amount of drug per unit mass decreases with increasing thickness of the enteric coating. In this study, the coating process is tracked from start to finish on an hourly basis by taking samples of pellets during production and testing those using BARDS (Broadband Acoustic Resonance Dissolution Spectroscopy). BARDS offers a rapid approach to characterising enteric coatings with measurements based on reproducible changes in the compressibility of a solvent due to the evolution of air during dissolution. This is monitored acoustically via associated changes in the frequency of induced acoustic resonances. A steady state acoustic lag time is associated with the disintegration of the enteric coatings in basic solution. This lag time is pH dependent and is indicative of the rate at which the coating layer dissolves. BARDS represents a possible future surrogate test for conventional USP dissolution testing as its data correlates directly with the thickness of the enteric coating, its integrity and also with the drug loading as validated by HPLC.