The pharmacokinetics of tranylcypromine enantiomers in healthy subjects after oral administration of racemic drug and the single enantiomers.

Abstract

The pharmacokinetics of the two enantiomers of tranylcypromine were evaluated in six healthy subjects after oral dosage of the racemate (20 mg of the sulphate) and the single enantiomers (10 mg of the sulphate) using an enantiospecific assay. Significant differences in AUC, Cmax, lambda(z), and CLR of the two enantiomers were observed both on administration of the racemate and of the individual enantiomers. The plasma concentrations and urinary excretion rates of (-)-tranylcypromine exceeded those of (+)-tranylcypromine. AUCs of the (-)-enantiomer [arithmetical means 197 ng ml(-1) h after the racemate, 130 ng ml(-1) h after the enantiomer] were greater than those of the (+)-enantiomer [26 ng ml(-1) h after the racemate, 28 ng ml(-1) h after the enantiomer] (P = 0.0001). No in vivo racemisation was detected. The power of the study was insufficient to establish any enantiomer-enantiomer interaction except for a possible interaction at the level of renal clearance (P = 0.013 for both enantiomers).

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Br J clin Pharmac 1993; 36: 363-365
The pharmacokinetics of tranylcypromine enantiomers in
healthy subjects after oral administration of racemic drug and
the single enantiomers
H. WEBER-GRANDKE, G. HAHN, E. MUTSCHLER, W. MOHRKE', P. LANGGUTH2 &
H. SPAHN-LANGGUTH
Pharmakologisches Institut fur Naturwissenschaftler der Johann Wolfgang Goethe-Universitat, Theodor-Stern-Kai 7,
Gebaude 75A, D-6000 Frankfurt/Main 70, lRohm Pharma GmbH, Dr-Otto-Rohm-StraBe 2-4, D-6108 Weiterstadt,
F.R.G. and 2Departement Pharmazie, ETH Zentrum, ClausiusstraBe 25, CH-8092 Zurich, Switzerland
The pharmacokinetics of the two enantiomers of tranylcypromine were evaluated in six
healthy subjects after oral dosage of the racemate (20 mg of the sulphate) and the
single enantiomers (10 mg of the sulphate) using an enantiospecific assay. Significant
differences in AUC, Cmax,
administration ofthe racemate and of the individual enantiomers. The plasma concentra-
tions and urinary excretion rates of (-)-tranylcypromine exceeded those of (+)-tranyl-
cypromine. AUCs of the (-)-enantiomer [arithmetical means 197 ng ml-1 h after the
racemate, 130 ng ml-' h after the enantiomer] were greater than those of the (+)-
enantiomer [26 ng ml-' h after the racemate, 28 ng ml-' h after the enantiomer] (P =
0.0001). No in vivo racemisation was detected. The power of the study was insufficient
to establish any enantiomer-enantiomer interaction except for a possible interaction at
the level of renal clearance (P = 0.013 for both enantiomers).
Xz, and CLR of the two enantiomers were observed both on
Keywords
tranylcypromine
enantiomers
pharmacokinetics
Introduction
Methods
The two enantiomers of the monoamine oxidase inhibitor
tranylcypromine are the two optically active trans-2-
phenylcyclopropylamines [(+)-tranylcypromine = 1S,
2R-(+)-trans-2-phenylcyclopropylamine; (-)-tranylcy-
promine = 1R,2S-(-)-trans-2-phenylcyclopropylamine].
While (+)-tranylcypromine has a much higher inhibitory
potency (in vitro 100 times, in vivo 10 times) than its
optical antipode, mainly on MAO-B [1, 2], (-)-tranyl-
cypromine exhibits 2-3 times greater inhibition of
presynaptic catecholamine re-uptake [3] and causes
increased catecholamine release [4]. In a previous study,
involving separate administration of (+)- and (-)-
tranylcypromine, a difference in their kinetics was
observed [5]. For analytical reasons it was not possible
to measure the concentrations of the two enantiomers
simultaneously in this study. In addition, any kinetic
interaction between the stereoisomers could not be
investigated. Therefore, we have developed an assay to
separate tranylcypromine enantiomers in biological
fluids in order to study the pharmacokinetics of the
tranylcypromine enantiomers after oral administration
of racemic tranylcypromine.
Six healthy subjects (one female, five male; aged 18-35
years), three of whom were investigators and all of
whom had given their written informed consent, partici-
pated in this investigation. Ethics committee approval
was obtained for the study from the University Clinics
of Frankfurt. The study was performed according to a
randomised cross-over design, and the three treatment
periods were separated by wash-out periods of 3 days.
The subjects received 10 mg (+)-tranylcypromine
sulphate, 10 mg (-)-tranylcypromine sulphate and 20
mg rac-tranylcypromine sulphate orally as 100 ml aqueous
solutions.
Venous blood samples (10 ml) were collected into
heparinized tubes prior to dosage and at 0.5, 1, 2, 3, 4,
5, 6, 7 and 8 h thereafter. The plasma was separated by
centrifugation at 1000 g for 20 min. Urine was collected
up to 8 h after dosage. Samples were stored frozen
(-80°C) in glass tubes until analysis.
Plasma (and urine) tranylcypromine enantiomer
concentrations were measured as follows: to 1 ml of
plasma (or 0.5 ml of urine) 1 ml borate/sodium hydroxide
buffer pH 11 (0.1 M), 20 ng (200 ng for urine) internal
Correspondence: Dr H. Spahn-Langguth, Pharmakologisches Institut fur Naturwissenschaftler, Theodor-Stern-Kai 7, Geb. 75A, D-
6000 Frankfurt/Main 70, FRG
363

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364
H. Weber-Grandke et al.
standard, S-(+)-amphetamine, and diethyl ether 5 ml
(containing 1.5% ethanol, by volume) were added.
After extraction the organic layer was transferred to a
second tube and evaporated to dryness.
The residue was derivatised using 120 ,ul o-phthaldial-
dehyde/N-acetyl-L-cysteine reagent [6]. After a reaction
time of 5 min the resulting diastereomeric derivatives
were resolved by h.p.l.c. on a Zorbax octadecylsilane
column (250 x 4.5 mm) eluted with a mixture ofsodium
phosphate buffer pH 6.5 (0.05 M), methanol and tetra-
hydrofuran (50:60:1, by volume) at a flow rate of 1.2 ml
min-'. The fluorescence of the eluate was monitored at
344/442 nm. The retention times ofthe derivatives ofthe
(-)-enantiomer and the (+)-enantiomer of tranyl-
cypromine and of the internal standard were 32.5, 35.0
and 25.0 min, respectively. The assay limit for plasma
was 0.5-1 ng ml- and the coefficient of variation was
less than 10% in the range from 5 ng ml-' to 100 ng
ml-1 for both tranylcypromine enantiomers [7].
Pharmacokinetic parameters were calculated using
standard methods. Extrapolated areas (of AUC and
AUMC) were less than 5% of the total areas.
The data were evaluated statistically according to the
cross-over trial design [8] using a non-parametric two-
way analysis of variance [9] and the sign test [10],
accepting P . 0.05 as significant. Confidence limits [11]
were calculated in addition to P values.
Results and discussion
The average plasma concentrations of both enantiomers
after administration of racemate and the single enan-
tiomers, respectively, are shown in Figure 1. There was
no evidence of racemisation of the tranylcypromine
enantiomers in vivo.
After administration of the racemate the plasma
concentrations of the (-)-enantiomer always exceeded
those of the (+)-enantiomer. Yet, for corresponding
samples after enantiomer dosage a reverse (-)/(+) ratio
was found in 5% of the samples (all at sampling times
2h).
The plasma concentrations of the sum of both enan-
tiomers after giving the racemate were mostly (at 90%
of all sampling points in the six individuals) higher than
those after administration of the single enantiomers, (P
< 0.01, sign test), and always higher after 2 h.
The pharmacokinetic parameters are summarized in
Table 1. Cmax values ranged from 2.5 to 46.5 ng mlF- for
(+)-tranylcypromine and from 33.6 to 104.6 ng mlF- for
(-)-tranylcypromine after dosage of the racemate. The
corresponding ranges after enantiomer dosage were
14.0 to 24.3 ngmlF for (+)-tranylcypromine and 14.8 to
87.5 ng ml-1 for (-)-tranylcypromine. Terminal plasma
half-lives were shorter for (+)-tranylcypromine (P <
0.05), for both racemate and enantiomer dosage. The
oral clearance of (+)-tranylcypromine always exceeded
that of (-)-tranylcypromine. Mean residence times
were significantly longer for (-)-tranylcypromine.
Renal drug clearances were low compared with total
clearances with average values of 24.9 ml min-1 for
(+)- and 15.3 ml min-1 for (-)-tranylcypromine after
racemate dosage and 17.7 ml min-1 for (+)- and 8.1 ml
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Short report
365
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Figure 1
(-)-tranylcypromine (rectangles) after oral administration of
20 mg racemic tranylcypromine sulphate (closed symbols) and
10 mg of the separate enantiomers (open symbols).
Mean plasma concentrations of (+)- (circles) and
min-1 for (-)-tranylcypromine after enantiomer dosage.
The total fraction of the (-)-tranylcypromine dose that
was excreted within the 8 h of urine collection always
exceeded that of (+)-tranylcypromine, which
accordance with the findings of Lang et al. [5].
Whilewehaveshownmarkeddifferencesinthekinetics
ofthe enantiomers oftranylcypromine, the power ofthe
study was insufficient to establish any enantiomer-
enantiomer interaction with the possible exception of an
interaction at the level of renal clearance.
If the enantiomer concentration differences are mainly
due to a stereoselective first-pass effect, variation in
hepatic extraction ratio, caused by drug-drug inter-
actions, liver diseases or genetic polymorphism, may
lead to an altered enantiomer ratio with implications for
the interpretation of concentration-effect relationships.
is in
This work was supported by the Deutsche Forschungsgemein-
schaft, the Doktor-Robert-Pfleger-Stiftung (Bamberg), and
a graduate research grant from Rohm Pharma GmbH
(H. W.-G.).
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(Received 19 November 1991,
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