In vitro characterization of cytochrome P450 catalysed metabolism of the antiemetic tropisetron.

The new 5-hydroxytryptamine type 3 (5HT3) receptor antagonist tropisetron is used in the treatment of chemotherapy-related nausea. The drug is extensively metabolized in man, with the enzymes involved in tropisetron biotransformation being unknown. Identification of these enzymes would make it possible to predict both interindividual variability in plasma concentrations and metabolic interaction potential.

Maprotiline metabolism appears to co-segregate with the genetically-determined CYP2D6 polymorphic hydroxylation of debrisoquine.

The plasma concentrations of the tetracyclic antidepressant maprotiline and its effect on histamine-induced bronchoconstriction were measured after single (50 mg) and multiple (50 mg twice daily) oral doses in healthy subjects. Histamine-induced bronchoconstriction was abolished after a single dose of maprotiline and this effect persisted throughout multiple dose treatment. The mean Cmax of maprotiline in six poor metabolisers (PM) of debrisoquine was 2.

Oxaprotiline: enantioselective noradrenaline uptake inhibition indicated by intravenous amine pressor tests but not alpha 2-adrenoceptor binding to intact platelets in man.

The optically active isomers of the racemic tetracyclic antidepressant oxaprotiline, R (-) oxaprotiline CGP 12,103 A (levoprotiline) and the S (+) oxaprotiline CGP 12,104 A, have been used as tools for a methodological Phase I study. Only the S (+) enantiomer CGP 12,104 A inhibits noradrenaline uptake. Intravenous amine pressor tests and ex vivo measurement of alpha 2-adrenoceptor binding to intact human platelets were compared with respect to their reliability in indicating CGP 12,104 A-induced amine uptake inhibition and possibly associated alpha 2-receptor down-regulation in healthy subjects.

Intravenous amine pressor tests in healthy volunteers. Within- and between subject variances and sex differences.

The pressor effect of intravenous tyramine (TYR) and noradrenaline (NA) has been evaluated, respectively, in 157 tests in 19 healthy unmedicated subjects, and in 202 tests in 24 similar subjects, all of whom took part in greater than or equal to 3 test sessions. The pressor dose (PD) that raised systolic blood pressure by 30 mm Hg (PD30) ranged from 2 to 8 mg for TYR, and from 3.5 to 17 micrograms.

Monoamine oxidase inhibition by phenelzine and brofaromine in healthy volunteers.

The two monoamine oxidase (MAO) inhibitors phenelzine and brofaromine given for 2 to 3 weeks were compared in six volunteers. Blood pressure sensitivity to intravenous tyramine increased 2.6-fold during phenelzine (60 mg/day) and 4.