High-performance liquid chromatographic method with coulometric detection for the determination of buspirone in human plasma by means of a column-switching technique.

A reversed-phase high-performance liquid chromatographic method with electrochemical detection has been developed for the determination of buspirone from human plasma. The separation was carried out by using a Supelcosil ABZ+ plus C18 reversed-phase column and 0.05 M potassium dihydrogenphosphate (pH 6.5)-acetonitrile (7:3, v/v) as the mobile phase. The compounds were detected by coulometry. Buspirone and the internal standard were extracted from the human plasma using Bond-Elut C18 solid-phase extraction cartridges. Following removal of the the highly lipophilic plasma components we applied a column-switching technique which reduced the duration of HPLC measurement from 60 min to 15 min. The limit of quantitation was found to be 100 pg/ml plasma.

Validated liquid chromatographic method for the determination of N-3-(2,2,5,5-tetramethyl-3-pirrolin-3-carboxamidopropylphthalimide hydrochloride), a novel antiarrhythmic agent in human plasma.

A simple high-performance liquid chromatographic method with ultraviolet absorbance detection has been developed to determine the concentration of N-3-(2,2,5,5-tetramethyl-3-pirrolin-3-carboxamidopropylphthalim ide hydrochloride; A-2545), a new antiarrhythmic agent from human plasma. Separation of the investigated compound and internal standard was achieved on a Nucleosil 7 C18 column with a 0.01-M potassium dihydrogenphosphate buffer (pH 2.5)-methanol (60:40, v/v) mobile phase. The detection was performed at 220 nm. During the determinations, buspirone served as the internal standard. The compounds were isolated from plasma on a Bakerbond C18 solid-phase extraction cartridge and the mean absolute recovery was 92.9%. The limit of quantitation was found to be 10 ng/ml. The bioanalytical method was validated with respect to linearity, within- and between-day accuracy and precision, system suitability and stability. All validated parameters were found to be within the internationally required limits. The developed analytical method for A-2545 was found to be suitable for application in pharmacokinetic studies and for human drug monitoring.

Determination of alpha-methyldopa in human plasma by validated high-performance liquid chromatography with fluorescence detection.

A sensitive reversed-phase gradient elution high-performance liquid chromatographic method with fluorescence detection has been developed for the determination of alpha-methyldopa (AMD) in human plasma. Separation of the investigated compound and the 3,4-dihydroxyphenylalanine (DOPA) internal standard was achieved on a Nucleosil 7 C18 column with a 5 mM heptanesulphonic acid sodium salt containing 0.05 M potassium dihydrogenphosphate (pH 3.2)-acetonitrile mobile phase. The composition of the mobile phase was changed according to a linear gradient time program. Detection was performed at 270 nm fluorimetric excitation and 320 nm emission. The compounds were isolated from plasma by Bond-Elut C18 solid-phase extraction. The limit of quantitation was found to be 10 ng/ml plasma. The assay was validated with respect to accuracy, precision and system suitability. All validated parameters were found to be within the 20% required limits. On the basis of the sensitivity, linearity and validation parameters the developed analytical method was found to be suitable for application in a bioequivalency study.

Relation of renal thromboxane A2 production to urine flow, electrolyte excretion and plasma renin activity in control state and drug induced hypotension.

The functional importance of renal TxB2 generation in the maintenance of elevated arterial blood pressure in essential hypertension was followed in 22 patients, using the method of sustained blood pressure decrease by i.v. sodium nitroprusside infusion. Linear correlation between urinary excretion of TxB2, urine flow, and sodium excretion could be established in both control and hypotensive periods. Presumably, changes in urinary excretion of TxB2 reflect a secondary intrarenal counterregulatory response.

Comparative bioavailability of alpha-methyldopa normal and film tablet formulations after single oral administration in healthy volunteers.

In a single dose, randomized, cross-over study, with one week of wash-out period, the relative bioavailability of Dopegyt tablets containing 250 mg alpha-methyldopa (AMD) and Presinol film tablets with identical active ingredient content was examined in 24 healthy volunteers. Since technologically two completely different preparations (a film-tablet and a non-film-tablet) having significantly different in vitro dissolution were to be compared, both preparations were compared to a third one, AMD solution (Dopegyt solution) with 250 mg/50 ml concentration. Plasma concentrations of the drug were measured for 24 hours post-dose, applying HPLC with fluorometric detection. Pharmacokinetic parameters calculated from individual data (AUC0-infinity, AUC0-t, Cmax, Cmax/AUC0-infinity, t(max)) were evaluated statistically. Wilcoxon's nonparametric test and the four-way variance analysis could not detect any significant difference at the usual a=95% probability level in these pharmacokinetic parameters of the two tablet preparations. For AUC0-infinity at the 90% probability level, the confidence interval was 0.883-1.237 (with an estimated geometric mean of 1.045), for the test/reference ratio of Dopegyt and Presinol tablets, thus the two preparations proved to be bioequivalent. The relative bioavailability of Dopegyt (test preparation) and Presinol (reference preparation) calculated from the AUC0-infinity values was 116.7+/-56.7% that also confirmed bioequivalence. The results of all the applied statistical tests suggest that Dopegyt and Presinol can be considered as bioequivalent preparations.

[Determination of paracetamol in urine by liquid chromatography]. / Paracetamol meghatározása vizeletböl folyadékkromatográfiával.

Since the biotransformation of paracetamol (Acetaminophen) is practically confined to conjugation, the quantitative determination of paracetamol excretion may provide important information on phase II of the drug metabolism. We elaborated a simple and rapid liquid chromatographic method for the assessment of paracetamol and its conjugated metabolites in the urine to be available for routine use in the clinicopharmacological laboratory. The persons involved in the trial were administrated 500 mg of paracetamol to be taken on an empty stomach in the morning. Subsequently, their urine was collected for 8 hours. The so-called free paracetamol of unchanged form excreted into the urine was measured from this 0 to 8 hours' urine fraction, then, after treating it with beta-glucuronidase/arysulphatase enzyme, the total amount of paracetamol released from the conjugate, as well as that of the existing free paracetamol, the so-called total paracetamol were determined. The urine extracts containing paracetamol obtained by ethylacetate, at pH 10, and dried under nitrogen stream were analysed by HPLC on an ODS column in an eluent of methanol and water mixture (3:7, v/v) in the presence of 3-acetaminophenol internal standard. The flow rate was 1 ml/min, the detection wavelength was 254 nm.

[Validity of a liquid chromatographic (HPLC) method for the determination of ticlopidine in human plasma]. / Validált folyadékkromatográfiás (HPLC) módszer a ticlopidin humán plazmából történó meghatározására.

A simple high-performance liquid chromatographic method for determination of ticlopidine in human plasma using UV detection was developed. The separation of the investigated compound and internal standard was achieved on "BST Rutin" 10, C18 BD column with a 0.01 M, (pH 4) potassium dihydrogen phosphate bufferacetonitrile-methanol (20:40:40 v/v) mobile phase. The detection was performed at 215 nm. The compounds were isolated from plasma by Bond Elut C18 solid-phase extraction, the mean absolute recovery was 84.9%. The limit of quantitation was 10 ng/ml, the limit of detection was 5 ng/ml. The assay has been validated with respect to accuracy, precision and system suitability. All validated parameters were found to be within the necessary limits. The developed analytical method for ticlopidine was found to be suitable for application in pharmacokinetic studies and human drug monitoring.

[Role of food interaction pharmacokinetic studies in drug development. Food interaction studies of theophylline and nifedipine retard and buspirone tablets]. / Etelinterakciós farmakokinetikai vizsgálatok helye és jelentósége a gyógyszerfejlesztésben. Teofillin retard, nifedipin retard és buspiron tabletták ételinterakciós vizsgálata.

Due to several mechanism, meals may modify the pharmacokinetics of drug products, thereby eliciting to clinically significant food interaction. Food interactions with the drug substance and with the drug formulation should be distinguished. Food interaction of different drug products containing the same active ingredient can be various depending on the pharmaceutical formulation technology. Particularly, in the case of modified release products, the food/formulation interaction can play an important role in the development of food interaction. Well known example, that bioavailability of theophylline can be influenced in different way (either increased, decreased or unchanged) by concomitant intake of food in the case of different sustained release products. The role and methods of food interaction studies in the different kinds of drug development (new chemical entity, modified release products, generics) are reviewed. Prediction of food effect response on the basis of the physicochemical and pharmacokinetic characteristics of the drug molecule or formulations is discussed. The results of three food interaction studies carried out the products of EGIS Pharmaceuticals Ltd. are also reviewed. The pharmacokinetic parameters of theophyllin 400 mg retard tablet were practically the same in both fasting condition and administration after consumption of a high fat containing standard breakfast. The ingestion of a high fat containing breakfast, increased the AUC of nifedipine from 259.0 +/- 101.2 ng h/ml to 326.7 +/- 122.5 ng h/ml and Cmax from 34.5 +/- 15.9 ng/ml to 74.3 +/- 23.9 ng/ml in case of nifedipine 20 mg retard tablet, in agreement with the data of literature. The statistical evaluation indicated significant differences between the pharmacokinetic parameters in the case of two administrations (before and after meal). The effect of a high fat containing breakfast for a generic version of buspiron 10 mg tablet and the bioequivalence after food consumption were studied in a single-dose, three-way (test and reference products administered after consumption of standard breakfast, as well as test product in fasting condition), cross-over, food effect bioequivalence study. According to the results, the test product--which, in a former study proved to be bioequivalent with the reference product in fasting state--is bioequivalent with the reference product under feeding conditions and the food intake influenced the pharmacokinetics of the test tablets.

[Pharmacokinetic study of nerisopam and its n-acetyl metabolite in rats]. / A nerisopam es N-acetil metabolitjának farmakokinetikai vizsgálata patkányokon.

Three doses were administered to the rats during the pharmacokinetic study of nerisopam and the plasma concentrations of nerisopam and its N-acetyl metabolite were determined parallelly by means of validated SPE-HPLC method developed by the authors. The pharmacokinetics of nerisopam could be described by a two-compartment open model in rats, it was absorbed rapidly and could be measured in plasma for about 8 hours. The peak plasma concentration of the N-acetyl metabolite was reached rapidly a little bit later than that of the parent compound, similarly to the human plasma, and it could be measured for about 12 hours. The pharmacokinetics of N-acetyl metabolite could be described by an one-compartment open model. The fast appearance of the metabolite and the Cmax and AUC 0-infinity values higher than those of nerisopam refer to an intensive "first-pass" metabolism. The AUC-dose curves indicate that supposingly the mechanism transforming the N-acetyl metabolites are not as fast as the acetylation.

[Human pharmacokinetic study of nerisopam and its n-acetyl metabolite]. / A nerisopam és N-acetil metabolitjainak humán farmakokinetikai vizsgálata.

It was established during the human phase I study of nerisopam, a new anxiolytic drug, that nerisopam (EGIS-6775) shows two, while N-acetyl metabolite (EGIS-7649) shows one compartmental pharmacokinetic behaviour. Acetylation of nerisopam is polymorph, so that volunteers belonging into slow or fast acetylating group show significantly different plasma concentration. Observed pharmacokinetic differences are primarily manifested in the absorption phase, and not in the elimination one. Accordingly, slow acetylators have higher nerisopam levels, while fast acetylators possess higher metabolite levels. Elimination phase is practically parallel for both compounds. At the same time, significant differences are found in the AUC and Cmax values. Nerisopam is rapidly absorbed, but N-acetyl metabolite is appeared especially fast in the blood. Our consideration is, that nerisopam undergoes significant "first-pass" metabolism process, the extent of which is different between the two acetylator phenotypes.