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 4.8-fold during brofaromine, whereas sensitivity to oral tyramine increased more during phenelzine (15.7-fold vs 8.5-fold). After withdrawal of phenelzine, pressor sensitivity to oral tyramine returned to control values within 2 and for more than 8 weeks. Relative bioavailability of conjugated tyramine was elevated sixfold by brofaromine and 11.6-fold by phenelzine. Urinary elimination of tryptamine increased during phenelzine and brofaromine to 12.7-fold and threefold, respectively. 3-Methoxy-4-hydroxyphenylglycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA) excretion decreased during brofaromine significantly by 72% and 49%, respectively. The nonsignificant decrease of MHPG excretion and the increase of intravenous tyramine pressor sensitivity caused by phenelzine are significantly related. The data suggest that the selective reversible MAO-A inhibitor brofaromine has a larger therapeutic safety than phenelzine.

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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 2.7‐fold greater than that in six extensive metabolisers (EM) and the mean AUC(0,48 h) was 3.5 times higher. The duration of the pulmonary effect of maprotiline after cessation of multiple dose treatment in EM was less than 3 weeks compared with at least 4 weeks in PM.

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.min-1 for NA. Coefficients of variation ranged from 3 to 47% and from 6 to 38% for TYR and NA, respectively, in the intra-subject comparison. The average inter-subject variation in the TYR PD30 was 22% for 8 females and 30% for 11 males; the corresponding variation in the NA PD30 was 27% (8 females) and 26% (16 males). While the average PD30 for NA was similar for males (10.8 micrograms/min) and females (10.9 micrograms/min), a sex-related difference was found for the PD30 of i.v. TYR: 4.4 mg for 11 males and 3.8 mg for 8 females. Additional results from volunteers who took part in fewer than 3 pressor test sessions supported this observation; PD30 of TYR 4.6 mg in 34 males vs 3.5 mg in 21 females. The large intra- and inter-subject variations in the i.v. TYR and NA pressor test results, and the sex difference in the systolic blood pressure response to i.v. TYR, should be considered in assessing the number and gender of subjects required in studies intended to show "significant" differences in the blood pressure response in amine pressor tests.

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. alpha 2-Adrenoceptor binding on intact human platelets did not distinguish between CGP 12,104 and CGP 12,103 A. However, amine pressor tests reflected the amine uptake inhibiting effect of CGP 12,104 A as a 5-fold decrease in tyramine pressor sensitivity and a 5-fold increase in noradrenaline pressor sensitivity.