Acute administration of levodopa-benserazide and tolcapone, a COMT inhibitor, Parkinson's disease.

Tolcapone, a catechol-O-methyltransferase inhibitor, can interfere with the metabolism of levodopa and dopamine and could prolong the motor effect induced by levodopa in parkinsonian patients. To test this hypothesis, we studied the motor effect induced by three acute administrations of a dose of levodopa-benserazide (Madopar) with either 200 mg or 400 mg of tolcapone or placebo, in a double-blind latin-square design. The duration of the on-phase could be compared in 10 parkinsonian patients suffering from square-shaped motor effect. In comparison to placebo, 200 mg and 400 mg of tolcapone significantly increased the mean duration of the on-phase by 61.7 min ( +/- 19.4 SEM) and by 72.2 min ( +/- 18.5), respectively. This clinical effect is suggested to be related mainly to the increase in levodopa area under the curve and half-life induced by tolcapone. The intensity in dyskinesias was increased by 400 mg of tolcapone. Tolcapone appears to be well tolerated and could be helpful as an adjuvant treatment to levodopa in parkinsonian patients with motor fluctuations.

Mixed linear and non-linear disposition of lazabemide, a reversible and selective inhibitor of monoamine oxidase B.

1. Single oral doses (100-300 mg) and multiple oral doses (100-350 mg 12 hourly for 7 days) of lazabemide were administered to 35 young and 40 elderly healthy subjects. Plasma concentrations of unchanged drug were determined to study the dose-concentration relationship. 2. The elimination phase time course of lazabemide concentrations indicated concentration-dependent elimination after both single and multiple dosing. Nevertheless, maximum concentrations and areas under concentration-time curves increased almost proportionally with dose and accumulation after chronic dosing was less than a factor of 2; steady-state concentrations were achieved by the third day of dosing. The apparent half-life determining accumulation was approximately 8-9 h. 3. Drug absorption commenced rapidly after a dose; two components to the absorption process were detectable in young subjects possibly due to simultaneous administration of multiple tablets at the higher doses. 4. Observations after single and multiple dosing were described with a compartmental model allowing for parallel saturable (population mean +/- s.d.: maximum elimination rate Vmax/F: 2.8 +/- 1.4 mg h-1; concentration at half-maximum elimination Km: 36 +/- 19 micrograms l-1) and first-order (CL/F 16 +/- 3.8 l h-1) elimination pathways. No important difference between the young and the elderly subjects was noted in absorption or disposition parameters of lazabemide.

Biochemical effects of high single doses of moclobemide in man: correlation with plasma concentrations.

The effects of high single doses of moclobemide (300, 450 and 600 mg given at the end of a standardized meal) on plasma levels of several catecholamines and their deaminated metabolites, and on plasma levels of pituitary hormones were determined in eight healthy young male volunteers in a randomized, double-blind, placebo-controlled study. Assessment of the i.v. tyramine potentiation and determination of the plasma levels of moclobemide were also performed. The tyramine sensitivity factor at 2 h after dosing was about 2.1, with no significant differences between the doses used. The inhibitory activity of moclobemide on MAO-A was reflected in significant reductions of plasma concentrations of DHPG and 5-HIAA. No clear differences were detected between the moclobemide doses. Prolactin plasma concentrations were only slightly increased after the two higher doses. The plasma concentrations of moclobemide were very much in agreement with those found in previous studies under similar experimental conditions. Thus, single oral doses of 300, 450 and 600 mg moclobemide demonstrated marked inhibition of MAO-A activity, whereas a single dose of 300 mg induced a near-maximum effect.

Cimetidine alters the disposition kinetics of the monoamine oxidase-A inhibitor moclobemide.

The influence of cimetidine on the absorption and disposition of moclobemide was examined in eight healthy male subjects. A single 100 mg intravenous and 100 mg oral dose of moclobemide was administered before and after 2 weeks of cimetidine administration (200 mg five times a day). The data on intravenous administration indicated that cimetidine produced a statistically significant alteration in the following disposition parameters (mean values for control versus cimetidine): systemic clearance, 46.6 versus 28.3 L/hr; mean residence time, 2.1 versus 3.2 hours; elimination half-life, 1.6 versus 2.3 hours. There was no significant difference in the steady-state volume of distribution. The absolute oral bioavailability of moclobemide increased significantly after cimetidine administration (54% versus 68%), as did the maximum plasma concentration after a single oral dose (575 versus 787 ng/ml). There were no differences in the mean absorption time or time to achieve maximum concentration. The values of systemic and apparent oral clearances of moclobemide after cimetidine administration were directly related to the corresponding control values before cimetidine. In contrast, the percentage change in clearance was essentially independent of the corresponding initial control clearance value.

Pharmacokinetics of moclobemide after single and multiple oral dosing with 150 milligrams 3 times daily for 15 days.

This study was undertaken to determine the absolute bioavailability and steady-state concentrations of moclobemide after doses of 150 mg. In 14 healthy human volunteers, no differences in tmax, t 1/2 beta, C1/F, Cmax and AUC were found between a single oral dose of 100 mg and one of 150 mg. The mean absolute oral availability was 0.66 and 0.69 respectively. Plasma concentration profiles of moclobemide on repeated dosing with 150 mg 3 times daily for 15 days were essentially superimposable, although the mean concentration was higher than after the single 150 mg dose. This concentration increased over the first week and then remained relatively constant. Mean accumulation factors for moclobemide during the first week were 1.85 for Cmax and 3.0 for AUC. These values were higher than predicted from single-dose characteristics. There was a marked reduction in the variability of AUC and clearance (C1/F) values at steady-state compared with the first dose. Minimum plasma concentrations of the 2 metabolites, Ro 12-5637 and Ro 12-8095, were relatively stable throughout dosing. The exact mechanism of the decrease in systemic and oral clearance of moclobemide with time during multiple oral dosing is not known at present. Either moclobemide inhibits its own clearance or moclobemide metabolism is inhibited by one or more of its metabolites. The findings indicate that, if dosage needs to be adjusted during treatment with moclobemide, the changes should be made carefully and at intervals of not less than 1 week.

Absorption and disposition of moclobemide in patients with advanced age or reduced liver or kidney function.

Three different studies were conducted to assess the pharmacokinetics of moclobemide in subjects with conditions complicating dose determination. The first examined the absorption and disposition of moclobemide in an elderly population and compared these with results obtained in a group of normal young subjects. No significant differences were found between the groups in the intravenous (i.v.) parameters of disposition, and no differences with regard to disposition of the metabolite, Ro 12-8095. In addition, the minimum steady-state concentrations of moclobemide and the main plasma metabolite did not differ between the elderly and younger patients. In the second study, clearance tests in patients with cirrhosis of the liver confirmed that hepatic function is drastically reduced in this group of patients; it is therefore possible that moclobemide absorption and distribution might be influenced. In only 3 of the 12 patients investigated, slowly declining plasma concentrations after administration pointed to a severely limited elimination capacity for moclobemide. In the remaining 9 subjects, average values of several parameters changed significantly (t 1/2 beta, MRT and C1), whereas Vss and renal clearance were not significantly altered. In patients with kidney dysfunction, there were no differences in kinetics between patients undergoing hemodialysis and those who were not. Compared with normal healthy volunteers, no differences were found for renal patients, with the exception of the mean absorption time, which was significantly prolonged. From these studies it can be concluded that, pharmacokinetically, neither age nor renal impairment require adjusting the dosage of moclobemide. Patients with liver cirrhosis, however, need to have the usual dose reduced to one half or one third, or else the dosage intervals can be increased to prevent cumulation.

Comparison of the pharmacokinetics of moclobemide in poor and efficient metabolizers of debrisoquine.

A number of pharmacokinetics studies in which patients had been phenotyped and poor metabolizers for moclobemide found were analysed retrospectively. There were 27 subjects in all, aged between 19 and 75 years, and 5 of these were classified as poor debrisoquine metabolizers. Although there was a wide variability in the pharmacokinetic parameters observed, no consistent relationship was found between these and debrisoquine phenotype. Poor debrisoquine metabolizers all had values within the extremes for the efficient metabolism. This was true for both single and multiple dosing. This analysis is limited by the small number of subjects as well as its retrospective nature. Nevertheless, the data suggest that no deviations of moclobemide pharmacokinetics should be expected in poor metabolizers of debrisoquine compared with normal metabolizers.

Moclobemide excretion in human breast milk.

1. Six lactating white women, aged 24-36 years, received a single oral dose of 300 mg moclobemide, between 09.00 h and 11.00 h, 3 to 5 days after the delivery of a full term neonate. 2. Complete milk collections were obtained before, 3, 6, 9, 12 and 24 h after drug administration by means of a breast pump. Venous blood samples were drawn before, and 0.5, 1, 3, 4.5, 6, 9, 12, 24 h post-dosing. 3. Moclobemide, and its major metabolite (Ro 12-8095) were measured in milk and plasma samples using h.p.l.c. The active metabolite (Ro 12-5637) could only be detected in plasma. 4. Moclobemide and its metabolites were not detectable in 24 h plasma samples. Cmax, tmax and t1/2 for moclobemide were (mean +/- s.d.) 2.70 +/- 1.24 mg l-1, 2.03 +/- 1.19 h and 2.26 +/- 0.26 h, respectively. 5. The concentrations of moclobemide and Ro 12-8095 in milk were highest at 3 h after drug administration and the drug and metabolite were not detectable after 12 h. Ro 12-5637 was not detected in any milk sample. The percentages of the dose excreted as moclobemide and Ro 12-8095 were (mean +/- s.d.) 0.057 +/- 0.020% and 0.031 +/- 0.011%, respectively. An average 3.5 kg breast-fed neonate would therefore be exposed to only a 0.05 mg kg-1 moclobemide dose (approximately 1% of the maternal dose on the mg kg-1 basis). The low amount of moclobemide excreted into breast milk is unlikely to be hazardous to suckling infants.

Effect of food intake on the relative bioavailability of moclobemide (Ro 11-1163).

Twelve healthy adult volunteers received a single 100-mg tablet of moclobemide in an open-label crossover study designed to determine the influence of food on moclobemide absorption. Moclobemide was administered 30 min after a standard breakfast as well as under fasting conditions. Moclobemide absorption was rapid in the absence of food. Bioavailability parameters obtained when drug was taken 30 min after the meal suggested that the rate of absorption was slightly decreased in the presence of food (mean Tmax 0.71 h vs. 1.14 h), while the extent of absorption of moclobemide given with food was unaltered. The decreased absorption rate in the presence of food is not expected to be of clinical significance.