Uwe Timm

Flumazenil kinetics in the elderly

SummaryIn an open design, randomised, two-way cross-over study, a single 2 mg i.v. dose and a single 30 mg oral dose of flumazenil were each administered to a group of healthy young (n=6) and elderly (n=12) volunteers (male: female 2/1). Plasma samples were collected at intervals and intact drug was assayed.Both the IV and oral doses of flumazenil were very well tolerated by both age groups and no severe or unexpected adverse effects were observed. The main complaints were dizziness and headache, mainly after oral dosing, probably due to the higher Cmax and AUC following this route of administration. After 2 mg i. v. the disposition parameters in the two age groups (elderly/young) were very similar: volume of distribution (Vss): 0.88/0.901·kg−1; total body clearance (ClPL): 0.86/0.99 l·min−1; terminal elimination half-life (t1/2β): 1.02/0.91 h. After the 30 mg oral dose the mean Cmax of 87.6 ng·ml−1 (elderly) and 78.4 ng·ml−1 (young) were generally reached within 0.5 to 1 h. In 26% (elderly) and 23% (young), the absolute bioavailability of flumazenil was very similar.It is concluded that the absorption and disposition paramters of flumazenil were not significantly affected by aging.

Pharmacokinetics of Retinoids in Women after Meal Consumption or Vitamin A Supplementation

These studies were conducted to evaluate the pharmacokinetics of several retinoids after meal consumption or vitamin A supplementation to establish a reference for future assessment of teratogenic risks of retinoid therapeutic agents. In the first study, 36 healthy young female volunteers consumed single meals containing vitamin A amounts ranging from 1,305 to 169,474 IU. In the second study, 24 other female volunteers took vitamin A supplements at a dose level of 5,000, 10,000, or 25,000 IU/day for 60 days. Plasma concentrations of tretinoin, isotretinoin, 4‐oxo‐tretinoin, and 4‐oxo‐isotretinoin in samples collected during the studies were analyzed using a high‐performance liquid chromatography method with ultraviolet detection. Pharmacokinetic parameters for the retinoids were calculated using model‐independent methods. Plasma concentrations of tretinoin were not altered by meal consumption or vitamin A supplementation. Plasma levels of 4‐oxo‐tretinoin were below the assay detection limit (0.3 ng/mL) in the majority of samples collected throughout the studies. Linear relationships between dose and maximum concentration (Cmax) and dose and area under the concentration—time curve (AUC) for isotretinoin and 4‐oxo‐isotretinoin were derived from data from the meal study. For the most bioavailable formulation used in the supplement study, daily ingestion of 5,000 IU of vitamin A caused increases of 141 ± 53% and 171 ± 77% from baseline in the 24‐hour AUCs of isotretinoin and 4‐oxo‐isotretinoin, respectively. Dose‐related increases in systemic exposure to retinoids were observed after ingestion of vitamin A by means of a meal or a supplement. Findings from these studies can be used as a basis for future safety evaluations of retinoid compounds.

Determination of a new non-benzodiazepine anxiolytic and its O-demethyl metabolite in plasma by high-performance liquid chromatography using automated column-switching

An highly sensitive and fully automated high-performance liquid chromatographic assay was developed for the determination of a novel non-benzodiazepine anxiolytic (I) [(R)-2-(methoxymethyl)-1-[(7-oxo-8-phenyl-7H-thieno[2,3-a]quinolizin+ ++- 10-yl)carbonyl]pyrrolidine] and its O-demethyl metabolite (II) in plasma, using column-switching for direct injection of plasma samples. After dilution in internal standard solution, the sample was injected onto a pre-column (17 mm x 4.6 mm) dry-packed with pellicular C18 reversed-phase material. Polar plasma components were removed by flushing the pre-column with water-acetonitrile (90:10, v/v). Retained substances, including I and II, were backflushed onto an analytical column, separated by gradient elution and detected by means of fluorescence detection (excitation, 304 nm; emission, 475 nm). After washing the analytical column and re-equilibrating the pre-column, the system was ready for the next injection. The limit of quantification for I and II was 0.25 and 0.5 ng/ml, respectively, using a 350-microliter specimen of plasma. The practicability of the new method was demonstrated by analysis of more than 300 plasma samples from a tolerance study performed with human volunteers. Owing to its high sensitivity, the method can be used to calculate pharmacokinetic parameters of compounds I and II in man after a single oral dose of about 1 mg of I.

Determination of the oral platelet aggregation inhibitor Sibrafiban® in rat, dog, and human plasma utilising HPLC-column switching combined with turbo ion spray single quadrupole mass spectrometry

A sensitive and selective HPLC-column switching method with single quadrupole mass spectrometric detection was developed for the simultaneous determination of the oral platelet aggregation inhibitor Sibrafiban (double protected prodrug), its prodrug and the active metabolite in rat, dog, and human plasma. The three analytes together with their tri-deuterated internal standards were isolated from plasma by protein precipitation (0.5 M perchloric acid). The de-proteinated samples were injected onto a standard-bore trapping column (4.0 mm i.d., LC-ABZ) of an HPLC-column switching system. Polar plasma components were removed by flushing the trapping column with ammonium formate (pH 3.6; 5 mM). Enriched compounds (including the analytes of interest) were backflushed onto a narrow-bore analytical column (2.1 mm i.d., Inertsil ODS-2) and separated by gradient elution (formic acid/ methanol). The whole effluent (200 microl/min) from the analytical column was passed to the turbo ion spray interface without splitting. Selected ion monitoring (SIM) was used for mass spectrometric detection. The limit of quantification for all three analytes was 1 ng/ml, using a 250-microl specimen of plasma. The mean precision and inaccuracy for the three analytes in all species were < 6 and < 5%, respectively. The practicability of the new analytical method was demonstrated by the analysis of about 500 rat and dog plasma and about 14,000 human plasma samples. The new method represents a successful example for the application of LC single MS with ionspray ionisation to the analysis of small molecule drugs in biological matrices from toxicokinetic studies and large clinical trials.

Pharmacokinetics and metabolism of the dipeptidyl peptidase IV inhibitor carmegliptin in rats, dogs, and monkeys.

The pharmacokinetics and excretion of carmegliptin, a novel dipeptidyl peptidase IV inhibitor, were examined in rats, dogs, and cynomolgus monkeys. Carmegliptin exhibited a moderate clearance, extensive tissue distribution, and a variable oral bioavailability of 28–174%. Due to saturation of intestinal active secretion, the area under the plasma concentration–time curve (AUC) in dogs and monkeys increased in a more than dose-proportional manner over an oral dose range of 2.5–10 mg/kg. Following oral administration of [14C]carmegliptin at 3 mg/kg, > 94% of the radioactive dose was recovered in 72-h post-dose from Wistar rats and Beagle dogs. Virtually, the entire administered radioactive dose was excreted unchanged in urine, intestinal lumen, and bile. Approximately 36%, 29%, and 19% of the dose were excreted by respective routes. Consistently, in vitro, carmegliptin was highly resistant to hepatic metabolism in all species tested. Based on in vitro studies, carmegliptin is a good substrate for Mdr1/MDR1. Breast cancer resistance protein (Bcrp) is not expected to be involved in the transport of carmegliptin since in vitro carmegliptin was not significantly transported by this transporter. The very high extravascular distribution of carmegliptin in the intestinal tissues, as demonstrated in Wistar rats and Beagle dogs, could play a significant role in its therapeutic effect.

Oral platelet aggregation inhibitor Ro 48-3657 : Determination of the active metabolite and its prodrug in plasma and urine by high-performance liquid chromatography using automated column switching

A sensitive and highly automated high-performance liquid chromatography (HPLC) column-switching method has been developed for the simultaneous determination of the active metabolite III and its prodrug II, both derivatives of the oral platelet inhibitor Ro 48-3657 (I), in plasma and urine of man and dog. Plasma samples were deproteinated with perchloric acid (0.5 M), while urine samples could be processed directly after dilution with phosphate buffer. The prepared samples were injected onto a pre-column of a HPLC column switching system. Polar plasma or urine components were removed by flushing the precolumn with phosphate buffer (0.1 M, pH 3.5). Retained compounds (including II and III) were backflushed onto the analytical column, separated by gradient elution and detected by means of UV detection at 240 nm. The limit of quantification for both compounds was 1 ng/ml (500 microl of plasma) and 25 ng/ml (50 microl of urine) for plasma and urine, respectively. The practicability of the new method was demonstrated by the analysis of about 6000 plasma and 1300 urine samples from various toxicokinetic studies in dogs and phase 1 studies in man.

Determination of the partial benzodiazepine receptor agonist Ro 16-6028 in plasma by capillary gas chromatography with nitrogen-selective detection after conversion into the ethyl ester derivative.

A highly sensitive capillary gas chromatographic method was developed to determine plasma levels of a novel partial benzodiazepine receptor agonist in man following the very low therapeutic doses required for anxiolysis. The compound was isolated from plasma by liquid-liquid extraction at basic pH, converted into the ethyl ester analogue by a two-step procedure, separated from plasma constituents by capillary gas chromatography and quantified by means of nitrogen-selective detection. Because of the thermolabile tert.-butyl ester function, the agonist could not be gas chromatographed without degradation. Formation of the far more stable ethyl ester analogue was achieved by treatment with hydrogen chloride in ethanol, followed by an ethylation step with diazoethane. The high sensitivity of the new method (about 100 pg/ml, using 1-ml plasma specimens) allowed the monitoring of plasma levels of the agonist for up to 8 h (about three elimination half-lives) after a single 0.1-mg oral dose to human volunteers. The practicability of the procedure was demonstrated by the analysis of more than 600 plasma samples from clinical studies performed with human volunteers.