QSPR studies on the photoinduced-fluorescence behaviour of pharmaceuticals and pesticides.

Fluorimetric analysis is still a growing line of research in the determination of a wide range of organic compounds, including pharmaceuticals and pesticides, which makes necessary the development of new strategies aimed at improving the performance of fluorescence determinations as well as the sensitivity and, especially, the selectivity of the newly developed analytical methods. In this paper are presented applications of a useful and growing tool suitable for fostering and improving research in the analytical field. Experimental screening, molecular connectivity and discriminant analysis are applied to organic compounds to predict their fluorescent behaviour after their photodegradation by UV irradiation in a continuous flow manifold (multicommutation flow assembly). The screening was based on online fluorimetric measurement and comprised pre-selected compounds with different molecular structures (pharmaceuticals and some pesticides with known 'native' fluorescent behaviour) to study their changes in fluorescent behaviour after UV irradiation. Theoretical predictions agree with the results from the experimental screening and could be used to develop selective analytical methods, as well as helping to reduce the need for expensive, time-consuming and trial-and-error screening procedures.

[Stability study of oxaliplatin and doxorubicin for intraperitoneal administration with hyperthermia]. / Estudio de estabilidad de oxaliplatino y doxorrubicina para su administración intraperitoneal con hipertermia.

OBJECTIVE: To evaluate the in vitro physicochemical stability of oxaliplatin and doxorubicin when the in vivo hyperthermic intraperitoneal conditions are reproduced. METHODS: Three solutions were prepared, A (oxaliplatin 200 mg/L), B(doxorubicin 15 mg/L) and C (oxaliplatin 200 mg/L with doxorubicin 15mg/L) in glucose 5%. The three solutions were subjected to the maximum temperature reached in vivo (49° C) for two hours. Physical stability was focused on visual control of particles or precipitates in solutions, discharge of gases, odor and color. Samples were taken every 15 minutes and the chemical stability was evaluated by determining the concentration of oxaliplatin and doxorubicin remaining in the samples. Oxaliplatin concentrations were determined by atomic absorption graphite chamber while doxorubicin was determined by high performance liquid chromatography.The chemical stability criteria selected was the one described by the American Pharmacopoeia, which sets a permissible variation range between the 90-110% of the initial concentration. RESULTS: During the assay there was no appearance of particles, precipitates in the samples, discharge of gases, nor colour changes in the solutions. The samples showed a remaining concentration of oxaliplatin and doxorubicin within the 90-110% limit. The stability of the samples that follow to two cycles of freeze-thaw after hyperthermia was also found within the specified limits. CONCLUSION: A, B and c solutions in 5% glucose, are physically and chemically stable at 49° C for two hours. Under these conditions, these solutions could be used with guarantees of stability in patients with peritoneal carcinomatosis subsidiary of intraperitoneal hyperthermic chemotherapy based in these antineoplastic agents.

Objetivo: Determinar in vitro la estabilidad físico-química de oxaliplatino ydoxorrubicina en las condiciones de hipertermia utilizadas in vivo duranteel tratamiento de pacientes con carcinomatosis peritoneal, tras cirugía citorreductora.Métodos: Se prepararon tres disoluciones: A (oxaliplatino 200 mg/L), B(doxorrubicina 15 mg/L) y C (oxaliplatino 200 mg/L + doxorrubicina 15 mg/L)en glucosa al 5%. Las tres disoluciones se sometieron a la temperaturamáxima alcanzada in vivo (49º C) durante dos horas. La estabilidad física secentró en el control visual de partículas y/o precipitados en las disoluciones,el desprendimiento de gases, olor y color. Para controlar la estabilidad química,se extrajeron muestras cada 15 minutos desde el inicio del estudio yse determinó la concentración remanente de oxaliplatino y doxorrubicina enlas mismas. Las concentraciones de oxaliplatino se determinaron por absorciónatómica con cámara de grafito mientras que doxorrubicina se determinómediante cromatografía líquida de alta resolución. Como criterio deestabilidad química se seleccionó el establecido en la Farmacopea Americanaque establece un margen de variación permitido entre el 90-110% de laconcentración inicial.Resultados: Durante el tiempo de ensayo, no se observó la aparición departículas o precipitados, ni el desprendimiento de gases o cambios decolor en las disoluciones. Las muestras analizadas presentaron una concentraciónremanente de oxaliplatino y doxorrubicina dentro del límite de 90-110%. La estabilidad de las muestras sometidas a dos ciclos de congelación-descongelación tras la hipertermia también se encontró dentro de loslímites especificados.Conclusiones: Las disoluciones A, B y C en glucosa al 5%, son establesfísica y químicamente a 49º C, durante dos horas. En estas condiciones,podrían ser utilizadas con garantías de estabilidad en pacientes con carcinomatosisperitoneal subsidiarios de recibir quimioterapia intraperitonealcon hipertermia basada en estos agentes antineoplásicos.

[Population pharmacokinetics of gemcitabine applied to personalize the dosage used in cancer patients]. / Farmacocinética poblacional de gemcitabina aplicada a la personalización de su dosificación en pacientes oncológicos.

OBJECTIVE: To develop and internally validate a population pharmacokinetic model for gemcitabine and its metabolite 2',2'-difluorodeoxyuridine (dFdU); and to evaluate its predictive perfomance for personalizing the dosage used in cancer patients. METHODS: Gemcitabine and dFdU plasma concentrations were determined in 18 cancer patients. A 2-compartment pharmacokinetic model was implemented in the NONMEN VI program to determine the appropriate pharmacokinetic parameters. The power to identify the parameters was assessed by parametric bootstrap, and the internal model validation was performed using nonparametric bootstrap and visual and numerical predictive check methods. The final predictive performance of the model was assessed for accuracy and precision during the first (a priori) and second (a posteriori) chemotherapy cycles. RESULTS: The mean and interpatient variability of gemcitabine and dFdU clearance was 2.70 L/min (31.0%) and 0.0515 L/min (35.8%), respectively. The estimated distribution volume at steady state was 30 L for gemcitabine and 238 L for dFdU. Internal validation confirmed that the population pharmacokinetic model was appropriate for describing the plasma concentrations of gemcitabine and dFdU over time, as well as its variability in the study population. The accuracy and precision of a posteriori gemcitabine plasma concentrations improved by 67% and 46%, respectively, compared to the a priori prediction. CONCLUSION: The population pharmacokinetic model adequately characterised the gemcitabine and dFdU plasma concentrations in the study population over time, and can be used to accurately and precisely optimise gemcitabine dosing regimens in cancer patients.

Use of QSAR methods for predicting the chemiluminescent behaviour of organic compounds upon reaction with potassium permanganate in an acid medium.

In previous work, molecular connectivity computations were successfully used to predict the chemiluminescent behaviour of organic compounds upon reaction with common strong oxidants and the native fluorescence too; both of them in a liquid phase. The obtained results were used to develop new analytical procedures to the given compounds. For the first time, connectivity methods were used for a purely analytical purpose. In this work, we went deeper into the knowledge of direct chemiluminescence processes by using molecular connectivity in the form of QSAR methods to predict the chemiluminescence intensity produced by reactions between organic compounds (pharmaceuticals mainly) and potassium permanganate in a liquid phase. The choice of this oxidant was dictated by its being the most active by far in producing chemiluminescence. We used discriminant analysis to examine the results for 63 substances the emission intensity of which upon reaction with acid potassium permanganate was experimentally measured in a continuous-flow manifold. Descriptors were chosen by applying stepwise linear dicriminant analysis (LDA) to Snedecor F-values, using the smallest Mahalanobis distance, the minimum error on the test set and the lowest value of the Wilks'lambda as sorting criterion. The theoretical predictions thus obtained were checked against the experimental results for a set of 16 compounds not used in the previous theoretical computations the chemiluminescent behaviour of which was also experimentally assessed. The result was a hit rate of 87.5% in the predictions.

Theoretical prediction of the native fluorescence of pharmaceuticals.

At present, to search fluorescent compounds or to increase the native fluorescence is an active research line specially and not only with analytical purposes. On some analytical areas and from the early times of applications of fluorescence (mid-fifties) the fluorimeter was defined as the suitable detector for determination of pharmaceuticals and subsequently, this detection mode has been widely applied. Therefore, it is mandatory to develop new strategies to discover or to enhance in a simple way the native fluorescence of organic compounds to increase the number of analytes to be determined by direct fluorescence. In the present paper are studied further applications of a new tool suitable to increase the research in analytical field. Calculations on molecular connectivity and discriminant analysis are applied to a certain number of pharmaceuticals (and some pesticides) on which fluorescence behaviour was observed in an experimental screening or obtained from scientific literature. The screening tests were based on the on-line fluorimetric measurement by using a continuous-flow assembly. The screening comprised pre-selected compounds with different molecular structures. The theoretical predictions agree with the empirical results from the screening test.

Theoretical prediction of the photoinduced chemiluminescence of pesticides.

Although it is relatively easy to find chemiluminescent (CL) molecules working on the field of direct liquid phase (especially employing strong oxidants), the molecules found as chemiluminescent are normally very weak CL compounds for developing suitable analytical CL-procedures. Therefore, it is mandatory to develop new strategies to enhance in a simple way the native chemiluminescence of such a compounds, and even to increase the number of compounds to be determined by direct chemiluminescence. Photoinduced chemiluminescence (Ph-CL) results in a simple and easily on-line accessible strategy to solve these disadvantages. In the present paper, molecular connectivity, a topological method which allows an unique mathematical characterization of molecular structures by the so-named topological descriptors and their correlation with physical, chemical and biological properties of molecules was applied to predict the Ph-CL in liquid phase. Molecular connectivity calculations and discriminant analysis was applied to 72 pesticides for which either a Ph-CL or non Ph-CL behaviour was observed in an experimental screening. The screening test is based on the on-line photodegradation of pesticides by using an automated multicommutation based flow asssembly provided with a photoreactor consisting of 150 cm x 0.8mm PTFE tubing helically coiled around a 20 W low-pressure mercury lamp. Photodegraded pesticides are detected by direct chemiluminescence of the resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The screening comprised pesticides with different molecular structures and relevant members of the most important families of pesticides were tested (oxime carbamates, sulfonylcarbamates, thiocarbamates, 1,3,5-triazines, organophosphorous, hydroxybenzonitrile, sulfonylureas, phosphonic acid derivatives, imidazolinones, carboxamides, aryloxyalkanoic acids, 1,2,4-triazinones, etc.). The theoretical predictions agree with the empirical results obtained by means of the screening test performed in the multicommutation flow-assembly.

Photo-induced chemiluminescence-based determination of diphenamid by using a multicommuted flow system.

This manuscript deals with the application of molecular connectivity calculations to predict the photo-induced chemiluminescent behaviour of the family of herbicides grouped as amides. Several compounds of this group were theoretically studied by means of a general discriminant equation formerly obtained, being 18 of them (plus eight from the chloroacetanilide sub-group) predicted with a high probability as photo-induced chemiluminescent. Empirical confirmation of the chemiluminometric behaviour was performed with some few commercially available amide herbicides. On the basis of these results, a new multicommutation-photo-chemiluminescent method is proposed for the determination of the diphenamid. The method is based on the photodegradation of the pesticide and then the resulting photo-fragment solutions are oxidized by K(3)[Fe(CN)(6)] in sodium hydroxide medium, at room temperature and 80 degrees C, for the photodegradation and chemiluminometric oxidation, respectively. The studied calibration up to 5.0mgl(-1), revealed a linear dynamic graph up to 20mgl(-1). The reproducibility between days resulted in a R.S.D. (in slope %) of 2.8 (n=5) and the repeatability with a %R.S.D. (n=20) of 4.3. LOD (s/n=3) of 1mugl(-1) and sample throughput of 20h(-1). The influence of foreign compounds is also tested and the optimized flow assembly is applied to different kind of samples.

Search compounds with antimicrobial activity by applying molecular topology to selected quinolones.

Molecular topology was used to obtain substances with antimicrobial activity. Selected quinolones were employed to develop the corresponding connectivity functions and discriminant equation. Limiting functions were selected that allowed the discriminant function to more efficiently distinguish substances with and without antibacterial activity. Antibacterial tests were run to confirm the theoretically established activity.

Kinetics and equilibrium in insulin radioimmunoassay.

The kinetics of insulin reaction has been studied with its specific antibody immobilized on the inner wall of the reaction tube; the radioimmunoanalytical determination of such a substance is based on the reaction. Independent variables were labelled and unlabelled insulin concentrations, temperature, viscosity, and the medium's ionic strength. Biexponential kinetics was found to be dependent on the concentrations fitted to the models discussed in the paper. The effect of temperature shows activation parameters similar to the viscous flow energy of water, which suggests that the reaction is diffusion-controlled. The results of the viscosity analysis points at the clearly negative influence of viscosity upon the direct reaction rate. Ionic strength has a noticeable, though not relevant, effect which seems to indicate that the variation resulting from the glycerol addition is not due to the influence of the dielectric constant in the solutions used.

Use of molecular topology for the prediction of physico-chemical, pharmacokinetic and toxicological properties of a group of antihistaminic drugs.

We used molecular connectivity to search mathematical models for predicting physico-chemical (e.g. the partition coefficient, P), pharmacokinetic (e.g. the time of maximum plasma level, and toxicological properties (lethal dose, LD) for a group of antihistaminic drugs. The results obtained clearly reveal the high efficiency of molecular topology for the prediction of these properties. Randomization and cross-validation by use of leave-one-out tests were also performed in order to assess the stability and the prediction ability of the connectivity functions selected.

Search of a topological pattern to evaluate toxicity of heterogeneous compounds.

Molecular connectivity has been applied to the search of mathematical models able to predict the carcinogenic and teratogenic activity of a wide group of structurally heterogeneous compounds. Through the linear discriminant analysis and the diagrams of distribution of pharmacological activity, the classification criteria that minimizes the percentage of error are established. The easiness and speed of the calculation of the descriptors used in this work make the models developed useful in data bases containing a huge number of compounds.

Prediction of the chemiluminescent behavior of pharmaceuticals and pesticides.

The present paper deals with the first attempt to apply molecular connectivity calculations to predict a chemical property with analytical usefulness: the chemiluminescent behavior of substances when reacted with common oxidants in a liquid phase. Preliminary evidence when searching for new direct CL methods consisted of the examination of analyte reaction with a wide range of oxidants and media. This task, which results in time-consuming and trial-and-error expensive procedures, is necessary due to ensure empirical or theoretical rules for CL prediction are available. On the other hand, in quantitative structure-activity relationship studies, molecular connectivity is a topological method capable of describing the structure of a molecule by means of numbers named indices; subsequent regression in relation to the experimental values of the physical, chemical, or biological properties yields a series of functions called connectivity functions. Discriminant analysis was applied to 200 either chemiluminescent or nonchemiluminescent substances found either bibliographically or in an experimental screening. The method used for the selection of descriptors was a stepwise linear discriminant analysis from the Snedecor F-parameter. The classification criterion used was the minimum value of Mahalanobis. The quality of the discriminant function was calculated through the Wilks U-statistical parameter. Finally, the function was applied to a database including of more than 50,000 structurally heterogeneous compounds. The theoretical predictions were faced with the empirical evidence obtained through a continuous-flow manifold.

Optimization of a mathematical topological pattern for the prediction of antihistaminic activity.

Molecular topology was used to develop a mathematical model capable of classifying compounds according to antihistaminic activity. The equations used for this purpose were derived using multilinear regression and linear discriminant analysis. The topological pattern of activity obtained allows the reliable prediction of antihistaminic activity in drugs frequently used for other therapeutic purposes. Based on the results, the proposed pattern is seemingly only valid for drugs that interact with histamine through competitive inhibition with H1 receptors.