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Determination of dissociation constants of labile drug compounds by capillary electrophoresis.

The utility of capillary electrophoresis (CE) for determination of the negative logarithm of dissociation constants (pK(a)) of labile compounds was investigated. In this study pyridinyl-methyl-sulfinyl-benzimidazoles (PMSB's), which have both an acidic and a basic pK(a), were selected as a first set of model drug compounds. This is a group of compounds that are known to degrade in aqueous solutions under neutral and acidic conditions which thus may impair their pK(a) determination when using common batch techniques based on spectrophotometry or potentiometry. An additional set of model drug compounds, benzenesulfonic acid phenethyloxy-phenyl esters (BSAP's), which are labile at high pH, were also studied. It is demonstrated that pK(a) values can be determined with high precision and accuracy by CE for both these sets of model compounds because decomposition products and impurities can be sufficiently separated from the main component. Based on the results in this study, a general strategy is proposed and discussed for determination of pK(a) for labile compounds. Key steps comprise use of a stabilizing sample diluent, injection by electromigration, short analysis time, and characterization of the main component by UV-Vis spectra.

Benzimidazoles↗

Release characteristics of anionic drug compounds from liquid crystalline gels. Part II. The effects of ion pairing and buffering on the passive delivery of anionic drugs across non-rate-limiting membranes.

This is the second in a series of papers that report on the release and transport of a range of anionic drugs (diclofenac, salicylic acid) from liquid crystalline gels and ultimately on their use in transdermal delivery. The previous paper [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels for transdermal delivery. Part I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236] investigated passive release profiles across a non-rate-limiting membrane: here we report on the search for a suitable model enhancer (benzyl dimethyldodecyl ammonium bromide) for the transdermal delivery of anionic compounds. The results presented reveal a significant role for ion pairing and for buffering, analogous to those found in the investigations of cationic species (salbutamol) by Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2003. Iontophoretic and chemical enhancement of drug delivery. Part I. Across artificial membranes. Int. J. Pharm. 12, 41-55. The method of vehicle preparation is also investigated. It is shown that ion pairing of the drug with the enhancer decreases the amount of drug available for transport from the liquid crystalline gels into aqueous receptor media. This decrease is directly related to the ratio of the concentration of drug to that of the enhancer. Buffering the vehicle inhibits the ion-pair formation to some extent. Vehicle preparation was also found to influence the degree of ion-pair association. The inclusion of a similarly charged enhancer (oleic acid) to the drug was found not to impede the diffusion of the drug from the gels.

Administration, Cutaneous↗

Medicinal herb extract and a single-compound drug confer similar complex pharmacogenomic activities in mcf-7 cells.

Metabolite profiling and DNA microarray analysis of global gene expression profiles were employed to characterize the bioactivities of the herbal extract of Anoectochilus formosanus (AF), a popular folk medicine with anticancer activity, in MCF-7 cancer cells. The pharmacogenomic activities of this plant extract as a crude phytocompound mixture were compared to those conferred by the single-compound drug, plumbagin. A similar level of complexity in transcriptional regulation at the genomic level was observed for both AF extract- and plumbagin-treated MCF-7 cells, as revealed by the number of up- or downregulated genes as well as by the specific but distinct patterns found in the gene-clustering analysis. This finding offers evidence to support the search for fractionated medicinal herb extracts or phytocompound mixtures, in addition to single-compound drugs, as defined therapeutic agents.

Anticarcinogenic Agents↗

Biosensor analysis of the interaction between drug compounds and liposomes of different properties; a two-dimensional characterization tool for estimation of membrane absorption.

The interactions between 78 drug compounds and immobilised liposomes were investigated using an assay based on surface plasmon resonance technology. The drugs were screened at a single concentration and allowed to interact simultaneously with two different types of liposomes. When the drug-liposome responses are plotted against one another they generally fall into three distinct bands: low response-low percent fraction absorbed in humans (Fa), medium response-medium Fa, and high response-high Fa. For drugs with medium to high Fa values, basic compounds could be resolved from acidic and neutral compounds to a large extent. This technique has the potential to be utilized as a screening tool for binning novel compounds into low, medium, or high Fa based on a simple experimental measurement. The assay was applied to 11 kinase inhibitors, 9 thrombin inhibitors, and 11 carbonic anhydrase inhibitors highlighting a subset that may have incomplete intestinal absorption (low to medium Fa). Assay conditions were optimized making the assay suitable for routine analysis and for compound characterization early in drug discovery where solubility may be an issue.

Absorption↗

Enantiomeric resolution of drug compounds by liquid chromatography.

Novel techniques have recently emerged to separate chiral drug compounds into pure enantiomers. The mechanism, experimental difficulties, and applicability of these methods can very greatly, and the choices involved are not straightforward. The most significant new advances in the field of chiral separations have come from work done with liquid chromatographic systems and chiral stationary-phase columns. This review describes several commonly used approaches to chiral separation, dia-stereomeric derivatization, chiral mobile-phase additives, and three major types of chiral stationary phases. Although no single method can be judged superior for every drug application, it appears that chiral stationary phases have received the most attention recently and they are emphasized here.

Chromatography, High Pressure Liquid↗

The high cost of customization: compounding drugs.

Physicians wishing to make a special compound for an inpatient for the first time, should contact the pharmacy well in advance of its need. Physicians should consider that the cost of compounding is very expensive. Furthermore, it is often less accurate in its dose than manufactured products. This is particularly important to remember with regards to mg/kg dosing. Provided certain conditions are met, the pharmacy will specially compound a product for an inpatient, if it has the ability to do so. Currently, the pharmacy cannot compound or dispense products for outpatients, or provide special compounding services to the BUSM, labs, departments, or clinics. If there are any questions about what can or cannot be done in the way of special formulations, contact the Pharmacy.

Cost-Benefit Analysis↗

Ruggedness study of HPLC peptide mapping for the identity of a drug compound: a chemometrics approach.

A statistically more reliable approach than the traditional visual inspection of peptide maps to identify a drug compound is to generate a set of reference standards from a designed experiment that incorporates many possible factors that affect variation of peptide mapping. In fact, the experiment can be done for a ruggedness study as part of a high-performance liquid chromatography (HPLC) method validation. Once the ruggedness is proved with the study, those articles in the experiment may form a set of reference standards, and future articles can be compared to the set later to prove identity. A quantitative analysis of the ruggedness study can be done using a chemometrics approach, principal component analysis (PCA). The analysis is used to reduce the many channels of peptide maps to a few manageable dimensions. The scores projected onto the reduced dimensions are used to test factor effects of the ruggedness study. As a by-product, the analysis provides visual inspection of the set of articles in the experiment for any outliers and anomalies.

Antibodies, Monoclonal↗

Approach to the determination of hydrate form conversions of drug compounds and solid dosage forms by near-infrared spectroscopy.

Near-infrared (IR) spectroscopy is used for the rapid, nondestructive identification and quantitation of the hydrate form of drug compounds forming both single and multiple hydration states. Near-IR is shown to be useful in both bulk drug and in finished solid dosage forms. The capability of near-IR to nondestructively analyze samples allows the kinetics of hydrate form conversions to be measured directly in formulated products. In addition, the environmental conditions for stability of the individual hydration states are mapped out using near-IR spectroscopy. Detailed molecular mechanisms are given to account for the near-IR spectral changes that occur upon hydration. The technique is applied in both laboratory studies as well as in a process environment for at-line analysis of active pharmaceutical ingredient hydration state during pharmaceutical processing.

Absorption↗

N-methyl-2-pyrrolidone as a cosolvent: relationship of cosolvent effect with solute polarity and the presence of proton-donating groups on model drug compounds.

N-Methyl-2-pyrrolidone (methylpyrrolidone), a cosolvent which has been used in veterinary medicine and in transdermal delivery devices, was investigated as a cosolvent for model drug compounds of widely varying polarity. These compounds were digoxin, sulfamethoxazole, hydrocortisone acetate, theophylline, phenytoin, and reserpine. Methylpyrrolidone was found to be an extremely efficient cosolvent for low solubility polar drugs such as digoxin or drugs containing multiple proton-donating groups such as phenytoin. The increase in solubility observed in aqueous solutions of digoxin and phenytoin to which 0.2 volume fraction of methylpyrrolidone was added was 500x and 65x, respectively. Significant deviations from log-linear solubilization were observed with digoxin, sulfamethoxazole, phenytoin, and reserpine, indicating significant water-solute-cosolvent interactions.

Chemical Phenomena↗