Measurement of 5-HIAA levels in ventricular CSF (by LCEC) and in striatum (byin vivo voltammetry) during pharmacological modifications of serotonin metabolism in the rat

Summary The relationship between the concentrations of 5-hydroxyindoleacetic acid (5-HIAA) in the CSF and in the striatum has been evaluated in the rat by measuring the levels of this metabolite in ventricular CSF (by liquid chromatography coupled with electrochemical detection) and in the striatal extracellular fluid (byin vivo voltammetry) after administration of inhibitors of serotonin synthesis or degradation. Pargyline, NSD 1015 and-propyldopacetamide all caused an exponential decline of 5-HIAA in both CSF and striatum. For a given drug, the rate constants for 5-HIAA disappearance were identical in the CSF and in the striatal extracellular fluid. These results confirm the view that CSF 5-HIAA may serve as a good index of brain serotonin turnover.     

A single-strip mini-paper chromatographic method for rapid purity-control of 99mTc-labeled radiopharmaceuticals

A single-strip miniaturized paper chromatographic method (Mini-PC) was developed using 80%–90% acetone solvent for rapid purity-control of ^99mTc-radiopharmaceuticals. Routine ^99mTc-radiopharmaceuticals (eight kinds of kit made agents) and diluted agents (in which radiochemical impurities might be formed) were analyzed by Mini-PC and other methods. This showed that, compared with the other methods, the Mini-PC technique is useful for the simple and rapid routine analysis of radiochemical impurities of kit made ^99mTc-radiopharmaceuticals.     

Rapid hydroxylation of methtryptoline (1-methyltetrahydro-β-carboline) in rat: Identification of metabolites by chiral gas chromatography-mass spectrometry

Summary Racemic methtryptoline (1-methyltetrahydro--carboline) and 5-hydroxymethtryptoline-9-carboxylic acid (6-hydroxy-1-methyltetrahydro--carboline-1-carboxylic acid) were administered intraperitoneally to rats and the components of their urine was subsequently investigated by chiral gas chromatography-mass spectrometry. Methtryptoline rapidly became hydroxylated in the 5- and 6-position and excreted in urine. There was about a ninefold predominance of the S(–) enantiomer over the other in the 5-hydroxylated species, while the 6-hydroxylation produced a small excess of the R(+) enantiomer. About 75% of the injected dose of methtryptoline was recovered in the urine as 5- and 6-hydroxylated compounds during the first 24 h period, demonstrating that hydroxylation represents the major metabolic pathway. Treatment with 6-hydroxymethtryptoline-9-carboxylic acid led to a fivefold increase in the urinary excretion of 5-hydroxymethtryptoline during the first 24 h period with a predominance of the S(–)-enantiomer, indicating a much smaller conversion rate than from methtryptoline. It was concluded that hydroxylation of methtryptoline is a likely pathway for the natural formation of 5-hydroxymethtryptoline.     

Determination of free fractions of tricyclic antidepressants

Summary The plasma protein binding of amitriptyline, imipramine, clomipramine, and their primary demethylated metabolites were studied by means of a method combining dialysis and gas chromatography. Equilibrium in dialysis of serum containing amitriptyline and its metabolite nortriptyline was attained in about 0.5 h with the drug dissolved in the serum compartment, and in about 2 h with the drug passing from the buffer to the serum compartment.The calculation of free fractions was influenced by variations with dialysis time in the volumes of serum and buffer. Increase of pH in serum increased the protein binding of the weakly basic drugs studied, and made the Donnan distribution effects more pronounced. At pH 7.4, the Donnan effect was negligible.Binding parameters for the 6 tricyclic antidepressant substances studied were estimated for the binding to ₁-acid glycoprotein and for total binding in serum. For ₁-acid glycoprotein, the k-values ranged from 1·10⁵ to 8·10⁵ M^–1, and for pooled serum from 0.4·10⁵ to 8·10⁵ M^–1. The determined number of binding sites on the ₁-acid glycoprotein was, on average 0.87 for the 6 substances. In serum, the binding capacity was 2–14 times the concentration of ₁-acid glycoprotein.     

Dissolution test for felodipine tablets using chemical oxidation in situ to maintain 'sink conditions'

A test model is described for the determination of the dissolution rate of the vasodilator, felodipine, a derivative of dihydropyridine that is practically insoluble in water. ‘Sink conditions’ are maintained by means of an oxidizing agent, ceric sulphate, which reacts rapidly with dissolved drug molecules in the dissolution fluid. A pyridine derivative is formed quantitatively in the oxidation reaction. The amount of dissolved felodipine is calculated from the concentration of the pyridine derivative, as determined by reversed-phase liquid chromatography. Dissolution rates depend on the concentration of the oxidizing agent so that high concentrations accelerate dissolution. The dissolution test suggested for 25-mg felodipine tablets is performed in 500 ml fluid that contains 5 mM ceric sulphate in 0.12 M sulphuric acid. The test is performed on single tablets with USP paddle equipment. Dissolution rates for nine different tablet compositions are correlated to such bioavailability parameters as maximum plasma concentration and total area under the plasma concentration—time curve. Interferences and limitations of the method are discussed.     

Stability-indicating determination of adrenaline in injections containing procaine

Adrenaline was determined in injections containing procaine in a 1000-fold excess by reversed-phase high-performance liquid chromatography using UV detection at 205 nm and aqueous sulphuric acid (100 μmol/l) as eluent. The relative standard deviation was 2.1%, and the method was selective in the presence of adrenaline degradation products. Changes of the capacity factor with pH and ionic strength of the eluent were studied, and a simple model is suggested to explain the retention data.     

New detection schemes in liquid chromatography

A micropolarimeter interfaced to a liquid chromatograph is shown to be suitable for selective monitoring of the optically-active components in complex samples. When an optically-active eluent is used, indirect determination of even optically-inactive materials is possible, down to the level of 10 ng of an injected component. If a second chromatogram is obtained using the racemic analogue of the optically-active eluent, quantitation can be achieved without standards and without prior analyte identification. This concept is also applicable to the refractive index detector, the absorption detector and the conductivity detector in the special case of ion chromatography, and the ultrasonic detector in gas chromatography.     

Enrichment techniques and trace analysis with microbore columns in liquid chromatography

The advantages of microbore columns for trace analysis by liquid chromatography are identified, with reference to on-column enrichment techniques performed on analytical micro-columns. The selectivity and high sensitivity of the amperometric detector are utilized in combination with a microbore column for a number of pharmaceutical and bioanalytical analyses, including phenothiazines, parabens, sulphonamides, catecholamines, tetracyclines, vitamins, amino acids and dipeptides.     

The combined use of high-performance liquid chromatography and radioimmunoassay for the bioanalysis of nicomorphine and its metabolites

Methods have been developed for the determination of nicomorphine using reversed-phase HPLC with UV detection; for the simultaneous assay of morphine and mononicotinoylmorphine by a coupled normal-phase HPLC-radioimmunoassay method; and for conjugates of morphine and mononicotinoylmorphine by radioimmunoassay. The methods have been evaluated and applied to a pharmacokinetic study of nicomorphine administered intramuscularly.