# Abstract

 

## Purpose To study the pharmacokinetics, pharmacodynamics, and tolerability of rising single doses of macitentan, an endothelin receptor antagonist, in healthy male subjects. 

## Methods This double-blind, placebo-controlled study was performed in seven groups of eight healthy male subjects. Doses of 0.2, 1, 5, 25, 100, 300 and 600 mg or placebo (two subjects per group) were administered. Plasma macitentan and endothelin-1 and serum total bile salt concentrations were measured and analysed non-compartmentally. Plasma and urine were analysed qualitatively for the presence of metabolites and one of these, ACT-132577, was also measured quantitatively in plasma. Standard tolerability measurements were performed throughout the study. 

## Results Macitentan was slowly absorbed and, at a dose of 300 mg, the t~1/2~ (95% confidence interval, CI) was 17.5 h (14.1, 21.8). The dose-proportionality coefficient β for C~max~ (95% CI) was 0.83 (0.79, 0.87) indicating less than dose-proportional pharmacokinetics of macitentan. In plasma, a pharmacologically active oxidative depropyl metabolite, ACT-132577, was found whereas in urine two minor metabolites were detected. The t~1/2~ of ACT-132577 (95% CI) was 65.6 h (53.1, 80.9). Macitentan dose-dependently increased endothelin-1 concentrations up to 2.2-fold (95% CI 1.4, 2.4) at a dose of 600 mg, but had no consistent effect on total bile salts. Macitentan was well tolerated up to and including a dose of 300 mg, the maximum tolerated dose. Headache, nausea and vomiting were dose-limiting adverse events. 

## Conclusion The pharmacokinetic and tolerability profile of macitentan is consistent with a once-a-day dosing regimen and warrants further investigation in clinical studies. # Results 

## Subjects and tolerability Fifty-six healthy male Caucasian subjects (age range: 19--49 years, body weight range: 55.4--98.0 kg) participated in this study and all completed the study as per protocol. A summary of the adverse events reported during the study, including those adverse events judged to be unrelated to study medication, is provided in Table [1](#). No unexpected adverse events, signs of oedema and/or serious adverse events were reported and all events resolved without sequelae. Up to and including a dose of 300 mg, the adverse event profile of macitentan did not significantly differ from that of placebo, whereas more adverse events than in the placebo group were reported at a dose of 600 mg. In this latter dose group, 5 out of 6 subjects reported headache of moderate intensity, accompanied by nausea and vomiting in 2 subjects. Two cases of increased alanine aminotransferase to about 2 times the upper limit of normal or less were observed: in a subject who had received 600 mg of macitentan and the other in a subject who had received placebo. Both cases occurred 7 days after drug administration, whereas 48 h after administration liver enzymes were normal. In neither subject was a significant increase in aspartate aminotransferase, bilirubin or alkaline phosphatase noted, nor were there any changes in total bile salt concentrations. There were no clinically significant drug-related effects on vital signs, ECG and clinical laboratory variables. ::::table-wrap

::: caption
Overview of reported adverse events by treatment
:::

Adverse event Treatment (mg macitentan)

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0.2 1 5 25 100 300 600 Placebo\
Headache 0 0 0 2 1 2 5 3
Back pain 0 0 0 0 0 1 0 1
Hepatic function abnormal 0 0 0 0 0 0 1 1
Nausea 0 0 0 0 0 0 2 0
Rhinitis 0 0 0 0 0 0 2 0
Vomiting 0 0 0 0 0 0 2 0
Abdominal pain 0 0 0 0 0 0 1 0
Flushing 0 0 0 0 0 0 1 0
Leukocytosis 0 0 0 0 1 0 0 0
Nasopharyngitis 0 0 0 1 0 0 0 0
Neck pain 0 0 0 0 1 0 0 0

Number of subjects reporting adverse events after having received
macitentan (*n* = 6 per dose) or placebo (*n* = 14)

Adverse events reported more than once by the same subject were counted
once:::: 

## Pharmacokinetics The mean plasma concentration--time profiles and the pharmacokinetic variables of macitentan and its main metabolite are shown in Fig. [2](#), and Tables [2](#) and [3](#). Under fasting conditions, macitentan was absorbed slowly with a median t~max~ varying from 8 to 30 h for the different dose groups. After attainment of C~max~, plasma concentrations decreased slowly. The apparent terminal half-life could only be reliably estimated for the two higher dose groups and was about 16 h. The pharmacokinetics of macitentan showed a less than dose-proportional increase for C~max~ as indicated by a value for the dose proportionality coefficient β (95% CI) of 0.83 (0.79, 0.87). Formation of the depropyl metabolite was slow with maximum concentrations attained at least 30 h after dosing (Fig. [2](#), Table [3](#)). In comparison to the parent compound, plasma concentrations of the metabolite were higher and elimination was slower as demonstrated by mean t~1/2~ values varying from 40.2 to 65.6 h. This resulted in a total exposure (AUC~0−∞~) to the metabolite that was 2.7-fold (95% CI 2.5, 2.9) greater than that to macitentan at a dose of 600 mg. <figure> <p><img src="" /></p> <figcaption>Arithmetic mean plasma concentration–time profiles of macitentan (<em>top panel</em>) and ACT-132577 (<em>bottom panel</em>) in healthy subjects (<em>n</em> = 6 per group except for 600 mg dose where <em>n</em> = 5) after administration of a single dose of 0.2, 1, 5, 25, 100, 300 or 600 mg of macitentan</figcaption> </figure> ::::table-wrap
::: caption
Pharmacokinetic variables of macitentan in healthy subjects after
administration of a single dose of 0.2, 1, 5, 25, 100, 300 and 600 mg of
macitentan
:::

Dose (mg) *n* C~max~ (ng/ml) t~max~ (h) AUC~0--48~ (ng.h/ml) AUC~0−∞~ (ng.h/ml) t~1/2~ (h)

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0.2 6 4.0 (2.6 to 6.2) 8 (8--12) 85.9 (52.4 to 141) ND ND
1 6 17.9 (12.4 to 25.9) 8 (4--10) 439 (271 to 711) ND ND
5 6 93.4 (79.1 to 110) 8 (4--8) 2056 (1,855 to 2,278) ND ND
25 6 335 (264 to 425) 8 (4--30) 8,810 (7,412 to 10,472) ND ND
100 6 999 (643 to 1552) 8 (4--12) 25,281 (18,775 to 34,040) ND ND
300 6 1,847 (1,409 to 2,422) 30 (10--48) 67,109 (48,751 to 92,380) 103,007 (76,650 to 138,428) 17.5 (14.1 to 21.8)
600 5\* 2,967 (2,233 to 3,943) 12 (8--30) 96,530 (70,006 to 133,102) 127,104 (82,657 to 195,450) 13.4 (11.3 to 15.9)

Data are expressed as geometric means (and 95% CI) or for t~max~ the
median (and range)

ND = not determined because t~1/2~ could not be reliably assessed

\*One subject was excluded from the descriptive statistics because of an
atypical plasma concentration--time profile:::: ::::table-wrap
::: caption
Pharmacokinetic variables of ACT-132577 in healthy subjects after
administration of a single dose of 0.2, 1, 5, 25, 100, 300 and 600 mg of
macitentan
:::

Dose (mg) *n* C~max~ (ng/ml) t~max~ (h) AUC~0--48~ (ng.h/ml) AUC~0−∞~ (ng.h/ml) t~1/2~ (h)

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0.2 6 3.7 (2.6 to 5.2) 36 (30--48) 114 (77.8 to 168) ND ND
1 6 16.3 (12.6 to 21.2) 48 (30--48) 527 (415 to 670) ND ND
5 6 84.1 (74.2 to 95.4) 33 (30--48) 2,540 (2,117 to 3,048) ND ND
25 6 304 (271 to 342) 42 (30--48) 9,146 (7,297 to 11,463) ND ND
100 6 931 (674 to 1,287) 42 (30--48) 32,068 (22,727 to 45,249) ND ND
300 6 2,585 (1,759 to 3,798) 48 (48--72) 67,174 (45,343 to 99,515) 330,549 (257,489 to 424,340) 65.6 (53.1, 80.9)
600 5\* 3,688 (2,591 to 5,249) 48 (36--48) 104,968 (73,339 to 150,238) 342,084 (213,414 to 548,331) 40.2 (34.6, 46.7)

Data are expressed as geometric means (and 95% CI) or for t~max~ the
median (and range)

ND = not determined because t~1/2~ could not be reliably assessed

\*One subject was excluded from the descriptive statistics because of an
atypical plasma concentration--time profile:::: One subject in the 600-mg dose group was excluded from the pharmacokinetic analysis because of an atypical plasma concentration-time profile of both macitentan and its metabolite. The C~max~ values for parent and metabolite were within the range observed for the other subjects, but the elimination of both compounds was much slower. 

## Metabolic profiling The investigation of the metabolic profile showed that in plasma only two compounds could be identified containing bromine atoms, macitentan and its metabolite, ACT-132577. In urine, the presence of two other compounds was shown, one that corresponds to a metabolite formed by hydrolysis of either macitentan or ACT-132577, and the other compound, based on the molecular weight, corresponds to a glucoside analogue of ACT-132577. Because in urine no macitentan and ACT-132577 could be detected, the collected urine samples were not analysed for these compounds. 

## Pharmacodynamics Plasma endothelin-1 concentrations dose-dependently increased following administration of macitentan (Fig. [3](#)) and this effect was statistically significant for doses of 25 mg and higher. The maximum effect was observed with the dose of 600 mg, which increased endothelin-1 concentrations 2.2-fold (95% CI 1.4, 3.4) compared with placebo. Administration of macitentan had no dose-dependent effect on serum total bile salt concentration at single doses of up to 600 mg, although a small but statistically significant effect (*P* \< 0.05) was observed for the lowest dose (Fig. [3](#)). <figure> <p><img src="" /></p> <figcaption>Arithmetic mean (±SD) plasma endothelin-1 (<em>top panel</em>) and serum total bile salt (<em>bottom panel</em>) concentrations in healthy subjects after administration of a single dose of 0.2, 1, 5, 25, 100, 300 or 600 mg of macitentan (<em>n</em> = 6 per dose group) or placebo (<em>n</em> = 14). \*<em>P</em> \< 0.05 compared with placebo</figcaption> </figure>


Extracted trial result:
Outcome: Plasma endothelin-1 concentrations (continuous)
Intervention: macitentan dose of 600 mg
Comparator: placebo
Intervention group size: 6
Comparator group size: 14
Notes: The mean and SD are in bar chart (figure)