H. J. Dengler

Defective N-oxidation of sparteine in man: a new pharmacogenetic defect.

SummarySparteine, an antiarrhythmic and oxytocic drug, is metabolised by N1-oxidation. The sparteine-N1-oxide rearranges with loss of water to 2- and 5-dehydrosparteine. 18 (i. e., 5%) out of 360 subjects were unable to metabolise the drug. These persons, who were designated as nonmetabolisers, excreted almost 100% of the administered dose in urine as unchanged drug. The defective metabolism of sparteine was found to have a genetic basis. Sparteine-N1-oxidation appears to be determined by two allelic genes at a single locus where nonmetabolisers are homozygous for an autosomal recessive gene.

Polymorphic CYP2D6 mediates O-demethylation of the opioid analgesic tramadol

AbstractObjective: This study was designed to investigate whether the in vivo metabolism of tramadol was influenced by CYP2D6 polymorphism. Methods: The extent of tramadol O- and N-demethylation was calculated by determining the amounts of tramadol and O- and N-desmethyltramadol in 24 h urine after ingestion of a test dose of tramadol. The O- and N-demethylation rates were calculated by dividing the 24-h urinary excretion amount of tramadol by that of O-and N-desmethyltramadol. Volunteers were phenotyped for CYP2D6 polymorphism using sparteine as an in vivo probe. Results and conclusion: High correlation was found between tramadol-O-demethylation and sparteine oxidation in 71 extensive metabolizers of sparteine (rs= 0.544). The mean metabolic ratio of tramadol O-demethylation was significantly higher in poor metabolizers of sparteine than in extensive metabolizers (4.4 vs 0.8). These in vivo results confirm that tramadol O-demethylation is carried out to a large extent by the polymorphic CYP2D6.

Influence of the defective metabolism of sparteine on its pharmacokinetics

SummarySparteine is metabolized by N1-oxidation, which in some subjects is defective. The defect has a pronounced effect on the kinetics of the drug. In non-metabolisers elimination of sparteine proceeds entirely via renal excretion by a capacity-limited process, 99,9% of the dose being excreted as unchanged drug. In metabolisers the drug is mainly eliminated by metabolic degradation. Pronounced differences in β-phase half-life and total plasma clearance were observed between metabolisers (156 min; 535 ml · min−1) and nonmetabolisers (409 min; 180 ml · min−1).

Absorption of digoxin from the distal parts of the intestine in man

SummaryIn 12 patients undergoing coloscopy, 0.5 mg digoxin in aqueous alcoholic solution was injected into the transverse colon. The late maximum of the blood level curve at about 2 hours after the administration suggested delayed absorption of the glycoside. However, the 24 hour urinary excretion of 17±3.4% in 8 patients with normal colonic mucosa demonstrated extensive absorption in the distal part of the bowel. The results have been contrasted with the findings in 4 patients with ulcerative colitis who excreted only 1.66±0.6% of the given dose in 24 hours.

High-performance liquid chromatographic assay for the simultaneous determination of tramadol and its metabolites in microsomal fractions of human liver

A high-performance liquid chromatographic assay for the quantitative determination of the opioid analgesic tramadol and its metabolites is described. A homologue of tramadol [1-(m-hydroxyphenyl)-2-(N-ethyl-N-methylaminomethyl)cycloheptane-1 -ol hydrochloride] is used as internal standard. The assay allows the determination of tramadol O- and N-demethylation activity in vitro in microsomal fractions of human liver. Tramadol and its in vitro generated Phase I metabolites are extracted by a one-step extraction procedure from microsomal incubation mixtures using methylene chloride. Extraction efficiencies of tramadol, O-demethyltramadol and mono-N-demethyltramadol were 70, 91 and 94% respectively. The isocratic high-performance liquid chromatographic system employs a C18 reversed-phase column. The mobile phase is a mixture of methanol, ammonium hydrogencarbonate solution and ammonium hydroxide solution. Sensitivity of the assay was 0.5, 0.2 and 0.2 microgram/ml for tramadol, O-demethyltramadol and mono-N-demethyltramadol, respectively. Within-run precision of the overall assay was 13, 3.1 and 7.6% for tramadol, O-demethyltramadol and mono-N-demethyltramadol, respectively. Accuracy of the assay was determined as mean differences of concentrations added and found in microsomal fractions. It was -2.4% for tramadol, -0.85% for O-demethyltramadol and 0.32% for mono-N-demethyltramadol.

Bioavailability of m-octopamine in man related to its metabolism.

SummaryThe diminished sympathomimetic pressor activity of monohydroxylated phenylalkylamines after oral administration has been attributed to incomplete enteric absorption. Therefore, urinary excretion of the unchanged drug and its metabolites has been compared after intravenous and oral administration of3H-m-octopamine to eight patients. Identical amounts of3H-activity (80% of the dose) were excreted after the two routes of dosing, so enteric absorption has been assumed to be complete. Significant differences were found in the fraction of free urinarym-octopamine, which amounted to 10.5% of the dose after infusion and 0.58% after oral administration. The only metabolic pathways form-octopamine are deamination and conjugation. Following oral administration the percentage of conjugates was considerably higher than after intravenous infusion. This metabolic pattern appears typical of all phenylalkylamines with a hydroxyl group in themeta position. Ring hydroxylation to catecholamines was not observed. The enzymes mainly responsible for conjugation after oral administration are located in the gut wall. The resulting “first pass effect”, i.e. metabolism prior to the access to the central compartment, can account for the diminished pharmacodynamic effect after dosing by this route.

The physiological disposition of p-octopamine in man

SummaryAfter oral administration of 3H-p-octopamine (8 mg≙300 μCi) more 3H-activity (93% of the dose) is excreted in the urine within 24 h than after intravenous infusion (2 mg≙300 μCi) over 2.5 h (82% of the dose). This proves that p-octopamine is absorbed quantitatively in man. The absorption proceeds rapidly, peak plasma levels are reached between 30 and 60 min.The only metabolic pathways for p-octopamine are deamination and conjugation. The predominant step is oxidative deamination by monoamine oxidase (MAO) to p-hydroxymandelic acid. This acid represents 2/3 of the urinary 3H-activity after both routes of admistration.A quantitative difference is seen in the fraction of free p-octopamine which equals the amount of conjugated amine after infusion but is only 1/20 after oral administration. This indicates a higher total clearance after an oral dose which consequently explains the diminished efficacy on blood pressure after this route.Hydroxylation to catecholamines was not found.

Atypisches Carcinoidsyndrom mit vermehrter Ausscheidung von 5-Hydroxyindolessigsäure bei Pankreascarcinom

ZusammenfassungEs wird eine Patientin mit dem klinischen Bild eines atypischen Carcinoidsyndroms beschrieben, bei der die Ausscheidung der 5-Hydroxyindolessigsäure im Urin stark gesteigert war. Die pathologisch-anatomische Untersuchung ergab jedoch ein metastasierendes Pankreascarcinom, in dem keine argentaffinen Zellen nachzuweisen waren. Es wird die Vermutung ausgesprochen, daß es eine Gruppe von Pankreastumoren gibt, die biochemische Ähnlichkeiten mit den Carcinoiden haben.

Pharmacokinetic studies in man with sparteine

SummaryPlasma levels of sparteine were determined in two groups of 8 patients each of whom received 200 mg of sparteine sulphate (Depasan®) intravenously and orally. A method was developed for the determination of sparteine in biological fluids, relying on solvent extraction and gas chromatography. After oral administration, 69.4% of the sparteine was absorbed and peak plasma levels were reached after 46.5 min. After intravenous injection the plasma levels declined with a half life of 117 min. When sparteine is given intravenously, 34.2% of the dose administered is excreted in the urine in the next 24 h as unchanged sparteine. Two metabolites were found in the urine but have not yet been identified. They contribute only a few percent to the total urinary excretion of sparteine. Approximately 50% of sparteine is bound to plasma proteins. — The pharmacokinetics of sparteine after intravenous administration can be described in terms of a one-compartment model. —The tissue distribution of sparteine was studied in preliminary experiments in rats. The drug was accumulated in several tissues, with the greatest concentration in the lungs. The hypothesis is advanced that drugs, which are organic bases with high pKa-values and high lipid solubility, are concentrated mainly in the lungs, followed by the adrenals, spleen, and the heart.

Characterization of cyclosporine A uptake in human erythrocytes

More than 70% of cyclosporine A (CsA) is bound to erythrocytes at whole blood concentrations of 50–1000 ng·ml−1. Cytosolic CsA is bound to the erythrocyte peptidyl-prolyl cis-trans isomerase cyclophilin. Measurements of serum CsA levels under clinical conditions are hampered by a temperature-dependent translocation of CsA into erythrocytes during cooling of the probes to room temperature. In order to characterize the kinetics of CsA uptake and to find a specific uptake inhibitor, we developed a method to measure the velocity of uptake based on rapid cooling of the erythrocyte suspension.The total erythrocyte-binding capacity for CsA amounted to 43·10−5 nmol per 106 erythrocytes or 2.6·105 molecules per erythrocyte. Whereas the erythrocyte-binding capacity of CsA was temperature-independent between 10°C and 42°C, uptake kinetics of CsA were temperature-dependent. The Arrhenius plot for CsA uptake in human erythrocytes was linear and no transition temperature between 0°C and 42°C could be detected. Therefore the CsA uptake process in human erythrocytes did not fulfil the criteria of carrier-mediated transport.This indicates that CsA diffuses passively into human erythrocytes. Hence, erythrocyte CsA uptake cannot be specifically inhibited.