A novel HPLC-MS/MS method for the simultaneous determination of astemizole and its major metabolite in dog or monkey plasma and application to pharmacokinetics.

Astemizole (AST), a second-generation antihistamine, is metabolized to desmethyl astemizole (DEA), and although it has been removed from the market for inducing QT interval prolongation, it has reemerged as a potential anticancer and antimalarial agent. This report describes a novel high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for simultaneously determining the concentrations of AST and DEA in beagle dog and cynomolgus monkey plasma with simple preparation method and short retention time. Prior to HPLC analyses, the plasma samples were extracted with simple liquid-liquid extraction method. The isocratic mobile phase was 0.025% trifluoroacetic acid (TFA dissolved in acetonitrile) and 20 mM ammonium acetate (94:6) at a flow rate of 0.25 mL/min and diphenhydramine used as internal standard. In MS/MS analyses, precursor ions of the analytes were optimized as protonated molecular ions: [M+H](+). The lower limit of quantification of astemizole was 2.5 ng/mL in both species and desmethyl astemizole were 7.5 ng/mL and 10 ng/mL in dog and monkey plasma, respectively. The accuracy, precision, and stability of the method were in accordance with FDA guidelines for the validation of bioanalytical methods. Finally this validated method was successfully applied to a pharmacokinetic study in dogs and monkeys after oral administration of 10 mg/kg AST.

MALDI-tandem mass spectrometry imaging of astemizole and its primary metabolite in rat brain sections.

BACKGROUND: Matrix-assisted laser desorption/ionization (MALDI)-tandem mass spectrometry (MS)/MS is a proven reliable tool for visualizing the spatial distribution of dosed drugs and their primary metabolites in animal tissue sections. MATERIALS & METHODS: The rat brain tissue sections coated with dihydroxybenzoic acid as matrix, were analyzed by MALDI-MS/MS imaging experiments. The potential metabolites of astemizole in rat brain homogenate selected for MALDI-MS/MS imaging experiments were first identified by high-performance liquid chromatography coupled to an electrospray ionization source and a hybrid-quadrupole-linear-ion-trap mass spectrometer. RESULTS: Astemizole was observed to be heterogeneously distributed to most parts of the brain tissue slices including the cortex, hippocampus, hypothalamic, thalamus and ventricle regions, while its major metabolite, desmethylastemizole, was only found around ventricle sites. CONCLUSION: The results indicated that the dosed compound alone might be responsible for the CNS side-effects when drug exposures became elevated.

Determination of astemizole in pharmaceutical preparations using spectrophotometric methods.

UV absorption and second derivative spectrophotometric methods were developed for the determination of astemizole in commercial pharmaceutical formulations containing this compound alone. Solutions of astemizole in 0.1 M HCl:methanol (1:3) were used in the methods and the linearity range was 4.6-45.8 microg ml(-1) in both methods. The mean recoveries and relative standard deviations were calculated and the method was applied to two commercial preparations marketed in Turkey. Results were compared with the literature method, HPLC. Also, two new spectrophotometric methods are described for the simultaneous determination of astemizole and pseudoephedrine hydrochloride in their combination. In the first method, first derivative spectrophotometry, dA/dlambda values were read at selected wavelengths in zero-crossing points in the first derivative spectra of the mixture solution in 0.1 M HCl:methanol (1:3). In the second, ratio spectra derivative spectrophotometry, analytical signals were measured at the wavelengths corresponding to either maximums and minimums for both drugs in their solution in 0.1 M HCl:methanol (1:3) in the first derivative spectra of their ratio spectra. The procedures do not require any separation step. The mean recoveries were found satisfactory in the methods.

Determination of astemizole, terfenadine and flunarizine hydrochloride by ternary complex formation with eosin and lead(II).

A simple and sensitive spectrophotometric method has been established for the determination of astemizole(I), terfenadine(II) and flunarizine hydrochloride(III) based on ternary complex formation with eosin and lead(II). The method does not involve solvent extraction. The colour of the produced complex is measured at 547.5 nm for (I) and (III), while (II) is measured at 540.7 nm. Appropriate conditions were established for the colour reaction and for the eosin: Pb(II): drug ratio to obtain maximum sensitivity. Under the proposed conditions, the method is applicable over concentration range of 4.1-37.6, 11.8-47.2 and 2.4-19.1 microg x ml(-1) with mean percentage recovery of 99.20+/-0.63, 99.76+/-0.39 and 99.60+/-0.47% for (I), (II) and (III), respectively. The suggested method was applied for determination of (I), (II) and (III) in pharmaceutical preparations. Through the use of a non-ionic surfactant (methylcellulose), prior extraction of the drugs was unnecessary. The results obtained demonstrated that the method is equally accurate, precise and reproducible as the official or reported methods. For the purpose of enhancing the sensitivity, a fluorescence quenching method for determination of the studied drugs via ternary complex formation was also investigated. The detection limit for the studied drugs (I), (II) and (III) was 0.94-7.1 microg x ml(-1) with mean percentage recovery of 99.84+/-0.29, 99.24+/-0.36 and 99.34+/-0.26%, respectively. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by official or reference methods. Unlike other reported ion-pair techniques, the suggested methods have the advantage of being applicable for the determination of the three drugs in their pharmaceutical dosage forms without prior extraction. They are recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical techniques are of great importance.

Colorimetric determination of astemizole in bulk and in its pharmaceutical dosage forms using flow injection.

A continuous flow spectrophotometric method for determining 0.5-100 micrograms ml-1 of astemizole in pure and in dosage forms is suggested. It depends on forming a pinkish orange product which can be quantified spectrophotometrically at 495 nm. The coloured product was due to the action of N-bromosuccinimide on astemizole in alkaline medium and in the presence of a cetyltrimethylammonium bromide micellar medium. The procedure is automated and solutions can be analysed at a rate of 167 h-1 with a relative error of about 1.25%. The limit of detection is 0.5 microgram ml-1 (approximately 1.09 x 10(-6) M). The method is evaluated by a recovery study and by the analysis of commercial formulations.