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Biomedical subjects

J Vasiliades

Publications and source records attributed to J Vasiliades.

At least 19 recordsLinked to original sources
PubMed1979

Determination of therapeutic and toxic concentrations of doxepin and loxapine using gas-liquid chromatography with a nitrogen-sensitive detector, and gas chromatography-mass spectrometry of loxapine.

A gas-liquid chromatographic procedure is presented for the determination of therapeutic and toxic serum levels of doxepin and loxapine, using a nitrogen-phosphorus-sensitive detector. Amitriptyline is used as the internal standard. The method is accurate, sensitive and specific with no derivatization required prior to analysis. An advantage of the procedure is the small serum sample size needed for analysis and the selectivity and sensitivity of the detector, with the limit of detection being 3 and 2 microgram/l for doxepin and loxapine, respectively. Nine cases of doxenin and loxapine misuse are presented. Serum doxepin concentrations ranged from 113 to 439 microgram/l, with a loxapine concentration of 192 microgram/l observed in one patient. The presence of the tricyclics was identified and confirmed by gas chromatography-mass spectrometry and the mass spectrum of loxapine is reported.

Adult↗
PubMed1979

Disopyramide determination by gas chromatography, liquid chromatography, and gas chromatography--mass spectrometry.

Disopyramide is determined in serum by gas chromatography with a nitrogen-selective detector, by liquid chromatography, and by gas chromatography--mass spectrometry. Comparable results are obtained with the three techniques, with a within-run and between-run precision of 5 to 10% (coefficient of variation). Least-squares analysis of data on patients' sera, analyzed first by gas chromatography (y) and then liquid chromatography (x), gave a slope of 1.12; y-intercept, -0.31; standard error of estimate, 0.46; and correlation coefficient, 0.94. Comparison of patients' sera by gas chromatography (y) and then by gas chromatography--mass spectrometry (x) gave a slope of 0.94; y-intercept, 0.42; standard error of estimate, 0.38; and correlation coefficient, 0.97. Interferences observed when using one technique--for example, gas chromatography--can be eliminated by analyzing the sample extract with one of the other techniques.

Chromatography, Gas↗
PubMed1979

Gas-chromatographic determination of disopyramide in serum, with use of a nitrogen-selective detector.

In this procedure for disopyramide in serum, the drug is extracted into n-heptane/isobutanol (96/4 by vol), then back-extracted into 1 mol/L H2SO4. The acidic solution is made basic with sodium hydroxide, extracted with diethyl ether, and the extract evaporated. The residue is redissolved in ethanol and analyzed by gas-chromatography, with use of a nitrogen-selective detector. p-Chlorodisopyramide is used as internal standard. Concentration and instrument response for serum extracts are linearly related from 1 to 5 mg/L, the slope being 0.61, the y-intercept -0.10, the standard error of estimate 0.01, and the correlation coefficient 0.99. Within-run precision was 6 and 4% for 3 and 5 mg/L concentrations, respectively, with a between-run precision of 7% at the 3 mg/L concentration. Diazepam interferes, but procainamide, chlordiazepoxide, quinidine, lidocaine, propranolol, sulfanilamide, and many other basic drugs do not.

Chromatography, Gas↗
PubMed1978

A modified sensitive spectrofluorometric method for the determination of propranolol in serum.

A modification of the spectrofluorometric propranolol procedure of Shand and associates and Ambler and colleagues is presented. A 3-ml volume of propranolol in serum is made basic with sodium hydroxide and extracted with 1.5% isoamyl alcohol in n-heptane. The drug is back-extracted into a mixture of 0.01 M citric acid in 50% ethylene glycol and measured spectrofluorometrically with the use of 299 nm for excitation and 352 nm for emission. Excellent linearity is observed in the 25--200 ng/ml range. The effects of sodium hydroxide, citric acid, and ethylene glycol concentration on the procedure were investigated. Ethylene glycol--citric acid in water is a better back-extracting mixture from the organic phase than hydrochloric acid. Using pentyl acetate as the extracting solvent instead of isoamyl alcohol in n-heptane did not change significantly the amount of the drug extracted. Other extracting solvents investigated did not increase sensitivity. At high citric acid concentrations a decrease in fluorescence intensity was observed at 350 nm. Interferences from other drugs using this procedure were investigated. Quinidine, methaqualone, and procainamide interfere at therapeutic levels.

Citrates↗
PubMed1978

Pitfalls of the alcohol dehydrogenase procedure for the emergency assay of alcohol: a case study of isopropanol overdose.

We describe a case of ethanol and isopropanol ingestion that resulted in coma. The concentration of ethanol and isopropanol was 0.90 and 1.65 g/liter in serum and 3.12 and 5.34 g/liter in gastric contents. With an enzymatic (alcohol dehydrogenase) method for ethanol determination we obtained erroneous analytical results. Because of partial cross reactivity with isopropanol, ethanol concentration was overestimated and total alcohol (i.e., the contribution of isopropanol) was underestimated. This was recognized by measuring serum osmolality. Differences between measured and calculated serum osmolality that are not accounted for by the serum ethanol concentration as determined by an enzymatic ethanol method must be further investigated by specific methods to see if other alcohols are present.

1-Propanol↗
PubMed1976

A modified ultraviolet spectrophotometric method for the determination of theophylline in serum in the presence of barbiturates.

Ultraviolet spectrophotometry is the most commonly used technique for the determination of theophylline levels for therapeutic monitoring. Common interferences in most methods are barbiturates and xanthines. A modified method which eliminates interferences from barbiturates and most xanthines is presented. Theophylline is extracted from serum with chloroform/isopropanol at pH 7.4 back extracted into dilute hydrochloric acid and then the solution is made alkaline with sodium hydroxide. Barbiturate interferences are eliminated. Interference from caffeine, uric acid, 7-(2,3-dihydroxypropyl)theophylline, xanthine, and hypoxanthine are not observed. Theobromine, and the metabolite 3-methylxanthine interfere. Interference is not observed from quinidine, diazepam, salicylate, glutethimide, methylprylon, propranolol, methaqualone, dilatin and ethchlorvynol. Sulfanilamide, procainamide and chlordiazepoxide interfere.

Barbiturates↗
PubMed1976

Reaction of alkaline sodium picrate with creatinine: I. Kinetics and mechanism of formation of the mono-creatinine picric acid complex.

Spectrophotometric, kinetic, and nuclear magnetic resonance studies indicate that alkaline sodium picrate and creatinine react to form a 1/1 aduct between picric and creatinine, with a stability constant of log K= 4.26. Kinetic studies indicate that the forward reaction is first order with respect to picric acid, hydroxide, and creatinine concentration. The reverse reaction, the dissociation of the 1/1 complex, shows a complex dependence on hydroxide concentration. The expression for the observed pseudo-first-order rate constant in the presence of excess picric acid is: Kobsd = K1K0[P][OH] +[K2[OH]x. A value of K1K0 = 5.0 (mol/liter)-2s-1 is obtained. For accurate analytical results with this reaction, hydroxide concentration must be maintained at a constant value for both samples and standards.

Chemical Phenomena↗