Minimal biliary excretion and enterohepatic recirculation of metoclopramide in patients with extrahepatic cholestasis.

The biliary excretion and apparent oral clearance of metoclopramide (MCL) were determined after oral administration of 1 mg MCL/kg body weight to 10 patients suffering from extrahepatic cholestasis with nasobiliary tube for drainage of the common bile duct. A bilioduodenal endoprosthesis was subsequently fitted in 6 of these patients, i.e. the enterohepatic circulation was restored, and the apparent oral clearance was re-determined. Biliary excretion, comprising free MCL and the products of conjugation, accounted for less than 1% of the administered dose. In accordance with this, the median areas under the plasma concentration-time-curves AUC(0-15 h) in patients with intact and interrupted enterohepatic recirculation were of similar size. The pharmacokinetic values in patients with cholestasis (median apparent oral clearance 0.5 l.kg-1.h-1; median t1/2 4.5 h) were similar to those previously reported in patients with healthy liver function. We conclude that it is not necessary to adjust single doses of MCL in patients recovering from obstructive jaundice.

Pharmacokinetics and relative bioavailability of prajmalium bitartrate after single oral dosing.

Pharmacokinetics and relative bioavailability of the marketed prajmalium bitartrate tablet (Neo-Gilurytmal, CAS 2589-47-1) compared to an oral solution were investigated in an open, randomized, single-dose two-fold crossover study in 20 healthy male volunteers. One subject was identified to be a poor metabolizer. In the study population with normal metabolic status the two oral formulations proved to be bioequivalent with regard to the pharmacokinetic parameters Cmax, AUC(0-Tlast), AUC(0-infinity) and Ae(24h). tmax was prolonged after administration of the tablets. The relative bioavailability of prajmalium bitartrate from the tablet amounted to 112%. The poor metabolizer demonstrated in both oral formulations high plasma concentrations, increased AUCs and prolonged terminal half-lives as well as increased renal excretion of prajmalium bitartrate.

Transfer of metaclazepam and its metabolites into breast milk.

Ten young women took part in this study a few days after delivery (day 3 and day 5 post partum). Lactation had developed normally but the newborn infants were not breast-fed. The study was intended to investigate whether metaclazepam (Talis), a new 1,4-benzodiazepine, and some of its metabolites were present in breast milk. Levels were measured in the plasma and milk. The levels in the milk showed that metaclazepam, N-desmethylmetaclazepam and two of its metabolites with a lactam structure could be found in small amounts. Differences in metaclazepam and N-desmethylmetaclazepam concentrations in the breast milk on days 3 and 5 post partum are discussed.

Pharmacokinetics and metabolism of 14C isobytylnaphtyl acetic acid in rat.

After oral administration to rats, absorption of INAA was slow but complete. Plasma level curves reached a plateau for INAA as well as for the two metabolites, which were rapidly formed (MI and MII). The plateau concentration led to an increase of the apparent elimination half-life, which was short after i.v. administration due to the small volume of distribution and to the high rate of metabolism. In any case the half-life was independent of the dose and the pharmacokinetics of INAA remained linear from 1.5 to 15 mg/kg. The two rapidly formed plasma metabolites were eliminated more slowly than INAA. INAA and its metabolites were distributed only sparsely in all tissues under investigation, probably due to the high protein binding. Both routes of administration resulted in elimination of the radioactivity mainly by the urine. Besides the two main metabolites with known structures (MI and MII) small amounts of INAA and two additional metabolites were detected.

Absolute bioavailability of metoclopramide given orally or by enema in patients with normal liver function or with cirrhosis of the liver.

Single dose studies were performed with three different dosage forms of metoclopramide (0.25 mg/kg body weight) in patients with normal liver function (i.v. (Paspertin): n = 4, oral liquid preparation: n = 4, rectal micro-enema n = 4) and patients with histologically confirmed cirrhosis of the liver (i.v.: n = 6, oral liquid preparation n = 4, rectal micro-enema: n = 8). Drug plasma-concentrations were measured over 8 h by a specific gas chromatographic method. The median areas under the plasma concentration-time curves (AUC0-8) after i.v. and rectal administration were similar in both groups. In contrast, the median oral bioavailability was considerably higher in patients with cirrhosis of the liver (82%) than in patients with normal liver function (60%). It can be concluded from this study, that dosage adjustments may be necessary in oral treatment of patients with cirrhosis of the liver, especially if prolonged therapy is required.

Pharmacokinetics of n-propyl-ajmaline-bitartrate in elderly patients with ventricular ectopic activity.

11 patients (9m, 2f, median age 59 years) with ventricular ectopic activity of at least Lown grade III received 20 mg N-Propyl-ajmaline-bitartrate (N-PAB) p.o. Plasma concentrations of N-PAB were determined with HPLC from blood samples within 26 hours after administration. An open two-compartment model was used. In 8 patients with normal function of the liver and the kidneys, the median clearance of N-PAB was 6.86 ml/min/kg and the median volume of distribution was 1.56 l/kg. Two patients had a clearly diminished clearance of 1.58 ml/min/kg without obvious impairment of liver or renal function. One patient with chronic glomerulonephritis (plasma creatinine 3.4 mg/dl) had a N-PAB clearance of 2.79 ml/min/kg. None of the Spearman rank correlation coefficients between the pharmacokinetic parameters of N-PAB with age, plasma albumin/globulin-quotient, plasma creatinine and cholin-esterase were significant. All calculated parameters were in the range determined in young subjects. It is concluded that physiological changes with age do not lead to significant changes of the pharmacokinetics of N-PAB. On the other hand in patients with increased levels of plasma creatinine a diminished clearance of N-PAB can be expected. It is also possible that patients without an obvious impairment of liver or renal function may have diminished N-PAB clearance.

[Dose-effect relation of N-prajmalium bitartrate with control of plasma levels]. / Dosis-Wirkungs-Beziehung von N-Prajmaliumbitartrat unter Plasmaspiegelkontrolle.

15 patients with ventricular ectopic beats classified to at least Lown class III with more than 100 ventricular ectopic beats in one hour were treated with N-prajmalium bitartrate (NPAB) in increasing dosages. The first dosage of 4 X 5 mg/d has been increased by 5 mg in three steps of three days to a level of 4 X 20 mg/d. A resting ECG, the systolic time intervals and a 24 h ECG were registered before treatment and after every dose. The median PQ time increased from 170 msec to 200 msec, the increase becoming significant (p less than 0.05) with a dose of 4 X 5 mg/d NPAB and above. Frequency, QRS and the frequency-corrected QT time did not change significantly. At a dose of 4 X 10 mg/d NPAB the increase of the quotient pre-ejection period to ejection time PEP/LVET became significant, increasing continuously from 0.35 to 0.48. Six of the 15 patients showed a significant reduction of ventricular ectopic beats, couplets and salvoes. In two patients the antiarrhythmic effect was significant at 4 X 5 mg/d. With an increasing dose from 4 X 10 mg/d each responder showed a significant reduction of ventricular ectopy. The lowest effective plasma concentrations ranged from 15 to 213 ng/ml with a median value of 58 ng/ml and an upper quartile of 94 ng/ml. There was no significant difference in plasma concentrations between responders and non-responders.

Pharmacokinetic profile of metaclazepam (Talis), a new 1.4-benzodiazepine. Influence of different dosage regimens on the pharmacokinetic profile of metaclazepam and its main metabolite under steady-state conditions.

The pharmacokinetic parameters of the new 1.4-benzodiazepine metaclazepam (Talis) were investigated. In particular, the question of whether the drug and/or its main metabolite accumulates in the body under steady-state conditions was studied. Two dosage regimens were compared by a randomized two-way crossover design: a once-a-day dosing (15 mg metaclazepam in the evening, = A) versus a twice-a-day dosing (5 mg in the morning plus 10 mg in the evening, = B) over ten days in twelve healthy male volunteers. Plasma levels of metaclazepam and its major biotransformation product, N-desmethylmetaclazepam, were determined. Comparing the treatments, significant differences were found for Cmax, but not for AUC-3 and Tmax. These results are also valid for the comparison of days 1 and 10 of each treatment. Higher Cmax values for dosage regimen A were found but Tmax and Cl/F remained stable in both treatments taking into account that 12 hours after the first medication, another dosing took place in treatment B. Eight hours after application, plasma levels were markedly low, Cmax values after single-dosing were nearly twice as high as after multiple dosing. Therefore based on these pharmacokinetic findings, a second dosing seems to be necessary; the clinical relevance needs further investigation. It has been reported, in fact, that it is in general very difficult to demonstrate a correlation between blood levels and therapeutic effects for 1.4-benzodiazepines (1,2).

Pharmacokinetics of N-propylajmaline in relation to polymorphic sparteine oxidation.

In order to determine whether the metabolism of the antiarrhythmic drug N-propylajmaline is under the same genetic control as sparteine metabolism, the pharmacokinetics of this antiarrhythmic drug were studied in a groups of six extensive and four poor metabolizers of sparteine. Pronounced differences in terminal half-life, total plasma clearance, metabolic clearance and urinary excretion of N-propylajmaline were observed between extensive and poor metabolizers. A close relationship between the total clearance and metabolic clearance of N-propylajmaline and sparteine could be demonstrated. Clinically available N-propylajmaline is a 55% to 45% mixture of the i- and n-diastereomers. The extensive metabolizers exhibited stereoselective metabolism; the i-diastereomer was preferentially metabolized. Poor metabolizers were characterized by a loss of this stereoselective metabolism. Five subjects were treated for 7 days with a daily N-propylajmaline dosage of either 60 mg or 20 mg. Since a close relationship between the clearance of N-propylajmaline and the metabolic ratio of sparteine had been observed after single dosing the metabolic ratio of sparteine was used to predict N-propylajmaline steady-state plasma concentrations during multiple dosing. Only in two extensive metabolizers with a metabolic ratio less than 0.4 predicted and observed, steady-state plasma concentrations were in good agreement. In the other three subjects observed steady-state plasma concentrations were appreciably higher than predicted. In these three subjects metabolic N-propylajmaline clearance decreased indicating saturation N-propylajmaline metabolism during multiple dosing. The data indicate that N-propylajmaline metabolism is subject to a genetic polymorphism controlled by the sparteine/debrisoquine gene locus.

Metoclopramide kinetics at high-dose infusion rates for prevention of cisplatin-induced emesis.

Eleven male subjects aged 24 to 58 yr received cisplatin, 90 to 120 mg/m2 iv, in combination with other cytostatic drugs such as doxorubicin HCl and bleomycin. To prevent emesis, two high-dose metoclopramide regimens were started 2 hr before cytostatic therapy. Regimen A (n = 7) consisted of a loading dose infusion of 1 mg/kg/hr over 2 hr, followed by a maintenance infusion of 0.5 mg/kg/hr over 24 hr (total dose was 14 mg/kg in each cytostatic cycle). Regimen B (n = 6) consisted of half the metoclopramide dose. The following kinetics were derived from the metoclopramide steady-state plasma levels and the t1/2 of the elimination phase 26 to 38 hr after dosing (median value and range are listed): Steady-state plasma concentration in group A and group B was 750 (480 to 1520) and 360 (300 to 480) ng/ml plasma. Drug clearance in group A and group B was 0.67 (0.3 to 1.0) and 0.70 (0.5 to 0.8) l/hr/kg. Volumes of drug distribution in group A and group B were 4.4 (1.9 to 6.5) and 4.3 (3.2 to 5.9) l/kg. Values for the t1/2 in the elimination phase in group A and group B were 4.7 (3.0 to 5.4) and 4.3 (3.7 to 5.1) hr. It appears that metoclopramide kinetics at high doses were dose linear, i.e., without evidence of cumulation. There were few side effects; vomiting was effectively suppressed by both regimens.

Comparison of the pharmacokinetic profile of metaclazepam in old and young volunteers.

A single-centre, open, Phase I-study comparison of the pharmacokinetics of a single dose of metaclazepam 10 mg, a new 1,4-benzodiazepine has been done in 10 older and 20 younger volunteers. No important age-related effect was found on the kinetics of metaclazepam or its N-desmethyl derivative, the principal metabolite in man.

Metabolism and pharmacokinetics of metaclazepam (Talis), Part III: Determination of the chemical structure of metabolites in dogs, rabbits and men.

The metabolism of 7-bromo-1-methyl-2-methoxymethyl-5-(2'-chlorophenyl)-2, 3-dihydro-1H-1,4-benzodiazepine (metaclazepam, Talis) in animals and men is described. Based upon mass spectrometry fifteen metabolites could be identified. Qualitative and quantitative differences in the biotransformation products of metaclazepam in comparison with the well known metabolites of other drugs in the 1,4-benzodiazepine class could be demonstrated. Metabolites with a benzodiazepine-2-one structure representing the most characteristic feature of other 1,4-benzodiazepines and their metabolites, were found in trace amounts only. The major metabolic pathways of metaclazepam led via stepwise demethylation of the O-methyl and/or the N-methyl group to O-demethyl-metaclazepam (M 2), N-demethyl-metaclazepam (M 7) and bis-demethyl-metaclazepam (M 6). Further aromatic hydroxylation yielded the metabolite M 1. Two metabolites with amino-benzophenone structure (M 5, M 8) which are in general known to result from other 1,4-benzodiazepines could be detected. Additionally a 3-oxo-benzodiazepine (M 4) was found. Minor biotransformation pathways led to a chlorophenyl-bromo-benzodiazepine (M 9) by loss of the side chain from bis-demethyl-metaclazepam and N-demethyl-metaclazepam. By further oxidation and degradation the 2-oxo-benzodiazepine M 10 and the dihydro-quinazoline M 12 were formed. The respective N-methylated metabolites M 13 and M 16 were possibly generated by the same pathway. Still open is the formation of M 15, a 1-methyl-3-hydroxy-4-(2'-chlorophenyl)-6-bromo-1,2-dihydroquinoline and M 11, a 2-methyl-4-(2'-chlorophenyl)-6-bromo-quinazoline. The substitution of bromine by a hydroxyl group during the formation of M 14 can be explained by a NIH-shift mechanism. Quantitative investigations show that the methoxymethyl side chain in the benzodiazepine ring system of metaclazepam acts as an effective barrier with respect to the metabolic attack at position two. We assume that this barrier only can be overcome by complete side chain degradation. This multi-step reaction can hardly compete with more favourable and faster conjugation and elimination processes.

[Pharmacokinetics and biotransformation of N-propylajmaline hydrogen tartrate in man]. / Pharmakokinetik und Biotransformation von N-Propyl-ajmalin-hydrogentartrat beim Menschen.

10 and 20 mg of N-Propyl-ajmalin-hydrogentartrate (N-PAB, Neo-Gilurytmal) were administered i.v. and orally respectively to healthy volunteers. In the study 14C-labelled N-PAB was used. The pharmacokinetics and the metabolic behaviour was examined. A fast and complete absorption of the compound could be observed. The bioavailability was 78%. The terminal plasma elimination half-life (beta-phase) was in the range of 4 to 6 hours. A total of 33% of the administered radioactivity was excreted via the kidney. 35 to 48% of the radioactivity found in urine was unchanged N-PAB. The excretion-kinetics of the three main metabolites as well as of the parent compound were determined. The possible presence of non-metabolizers is suggested.