Effect of MAO-A inhibition on the pharmacokinetics of almotriptan, an antimigraine agent in humans

Abstract

Aims

To assess the effect of a reversible MAO-A inhibitor, moclobemide, on the single-dose pharmacokinetics of almotriptan and assess the clinical consequences of any interaction.

Methods

Twelve healthy volunteers received the following treatments in a randomized, open-label, two-way crossover design (with a 1 week washout between treatments): (A) one 150 mg moclobemide tablet every 12 h for 8 days and one 12.5 mg almotriptan tablet on the morning of day 8; and (B) one 12.5 mg almotriptan tablet on day 8. Plasma almotriptan was quantified by h.p.l.c.-MS-MS, while urinary concentrations were measured by h.p.l.c.-u.v. Vital signs, ECGs, and adverse events were evaluated after almotriptan administration. Treatment effects on pharmacokinetics and vital signs were assessed by analysis of variance.

Results

Mean almotriptan AUC was higher (483 ± 99.9 vs 352 ± 75.4 ng ml⁻¹ h, P = 0.0001) and oral clearance was lower (26.6 ± 4.00 vs 36.6 ± 5.89 l h⁻¹, P = 0.0001) when almotriptan was administered with moclobemide. Mean half-life was longer (4.22 ± 0.78 vs 3.41 ± 0.45 h, P = 0.0002) after coadministration with moclobemide. Renal clearance of almotriptan was unaffected by moclobemide. No serious adverse events occurred and no clinically significant vital sign changes were observed.

Conclusions

Moclobemide increased plasma concentrations of almotriptan on average by 37%, but the combined administration of these two compounds was well tolerated. The degree of interaction was much less than that seen previously for sumatriptan or zolmitriptan given with moclobemide.

Introduction

Migraine is a disease characterised by paroxysmal headache, usually unilateral, and frequently accompanied by generalized sensorial hyperaesthesia and gastrointestinal disturbances. Serotonin (5-HT) is a neurotransmitter located in the brain, spinal cord and myenteric plexus. It is also a local hormone released by platelets, enterochromaffin cells and paracrine cells in the thyroid. Serotonin acts on vascular and gastrointestinal smooth muscle and may be involved in the genesis of migraine attacks [1].

Serotonin acts on several receptor subtypes; 5-HT_1B/1D receptors are found on intracranial blood vessels in the main carotid arterial tree, and in pial and dural vessels where they mediate vasoconstriction [1–2]. Agonists of 5-HT_1B/1D receptors are used for the symptomatic relief of migraine. Almotriptan is a new 5-HT_1B/1D agonist under development for the treatment of acute migraine. The affinity of the compound for the 5HT_1A receptors is 70 times lower than that for 5-HT_1B/D receptors, while its affinity for the remaining serotonin receptors studied (5HT₂, 5HT₄) is negligible [3]. Almotriptan has no apparent behavioural or central side-effects in animal models [3].

Almotriptan is well absorbed orally, with an absolute bioavailability of around 70% [4]. The drug shows dose-linear pharmacokinetics and a mean elimination half-life of 1.4–3.8 h [5–6]. In humans, almotriptan is eliminated by various pathways. Approximately 40–50% of the dose is recovered unchanged in the urine; renal elimination probably occurs via active tubular secretion [6]. The balance of the dose is eliminated unchanged in faeces (approximately 5%) or is metabolised. Studies suggest that monoamine oxidase is primarily responsible for almotriptan metabolism in man; cytochrome P-450 (CYP3A4 and CYP2D6 isozymes) contributes to a lesser degree [6–7].

Moclobemide is an antidepressant that affects the monoaminergic cerebral neurotransmitter system by means of a reversible inhibition of monoamine oxidase (preferentially type A, MAO-A). The metabolism of noradrenaline and serotonin is decreased by this effect, and this leads to increased concentrations of these neuronal transmitters. After multiple dosing, plasma concentrations of moclobemide increase over the first week of therapy and remain stable thereafter. Moclobemide is almost entirely metabolised before its elimination from the body. Less than 1% of a dose is excreted renally in the unchanged form. Metabolism occurs largely via oxidative reactions on the morpholine moiety of the molecule. Moclobemide is metabolised by CYP2C19, and is an inhibitor of CYP2D6, CYP2C19, and CYP1A2 [8]. The elimination half-life of moclobemide is 1 - 2 h with a slight increase at higher doses [9, 10].

Antimigraine compounds in the triptan class (sumatriptan, and zolmitriptan) are metabolised to varying extents by monoamine oxidase type A [11, 12]. In fact, coadministration of oral sumatriptan or zolmitriptan with monoamine oxidase inhibitors is contraindicated in current product labelling [13]. Monoamine oxidase inhibitors raise plasma concentrations of these compounds and thus may result in increased side-effects. Almotriptan is also metabolised by MAO-A, but this pathway is less prominent for almotriptan relative to sumatriptan and zolmitriptan. A MAO-A inhibitor, such as moclobemide, would be expected to have only a modest effect on almotriptan pharmacokinetics.

The primary objective of this study was to measure plasma drug concentrations and assess the pharmacokinetics of almotriptan when administered as a single dose in the presence and absence of moclobemide. The secondary objective was to assess the clinical consequences of a pharmacokinetic interaction between almotriptan and moclobemide.

Methods

The study was conducted at Biokinetic Clinical Applications, Belfast, Northern Ireland. The protocol was approved by the local ethics committee prior to commencement, and all subjects provided written informed consent prior to enrolment. The study was conducted in accordance with the Declaration of Helsinki and subsequent amendments.

Subjects

Non-smoking males or females from 18 to 45 years of age and with a body mass index between 18 and 29 kg m⁻² were recruited. All females had a negative serum pregnancy test prior to entry into the study. Females of childbearing potential were using a medically acceptable, nonhormonal method of birth control. Subjects were determined to be healthy, based on the results of physical examination, detailed medical history, and clinical laboratory tests.

Seven women and five men completed all protocol requirements. All subjects were Caucasian, and the mean age was 33.6 ± 8.2 years. The mean weight was 66.5 ± 9.9 kg.

Study design

This study was a randomized, open-label, two-way crossover, pharmacokinetic study conducted in healthy volunteers. Subjects received the following treatments with a minimum 1 week washout from the last day of period I until day −1 of Period II: (A) One 150 mg moclobemide tablet at approximately 08.00 h and 20.00 h on days 1–8 and one 12.5 mg almotriptan tablet administered with the morning moclobemide dose on day 8 and (B) no drug administration on days 1–8 and one 12.5 mg almotriptan tablet at approximately 08.00 h am on day 8. Subjects fasted for 10 h prior to and until 4 h after the almotriptan dose on day 8. All medication was administered with 200 ml of water. During each study period, subjects spent approximately 3 days in the clinical research unit.

Clinical assessments

Subjects were asked daily about any symptoms or effects they might have noticed during the interval since the last query. Spontaneously reported events were also recorded.

Twelve-lead electrocardiograms were recorded prior to dosing and at 1, 3, and 6 h after the morning dose on days 7 and 8. Continuous Holter monitoring was performed during almotriptan dosing (just prior to the morning dose on day 7 through day 9). Supine blood pressure, heart rate, oral temperature, and respiratory rate were collected predose and at 1, 2, 3, 4, 6, 8, 12 and 24 h after dosing on day 7 and day 8.

Almotriptan concentration measurements

Blood samples for the analysis of almotriptan were collected just prior to the almotriptan dose and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 16, and 24 h after drug administration. Venous whole blood (7 ml) was collected into tubes containing sodium heparin. The tubes were centrifuged at approximately 1000 g for 10 min at approximately 4 °C. After centrifugation, the plasma layer was transferred to plastic storage vials, frozen and stored below −20 °C until assayed.

Heparinized plasma samples were assayed for almotriptan concentrations using a validated, sensitive and specific LC/MS/MS assay. Using this method, almotriptan and the internal standard (d6-almotriptan, a deuterated analogue of almotriptan) were extracted from 250 µl plasma using a Varian Prospekt 9200 automated in-line solid phase extraction system. Each sample was diluted with 250 µl of acetonitrile:water (10 : 90 v/v), and centrifuged. The cartridge (Varian Prospekt Bond Elute C18) was conditioned with acetonitrile, followed by acetonitrile:water (10 : 90 v/v). The sample was injected onto the cartridge. The loaded cartridge was washed with 10 mm ammonium formate (pH 4.0):acetonitrile (50 : 50 v/v) and eluted with 10 mm ammonium formate (pH 4.0):acetonitrile (18 : 82, v/v). Effluent (100 µl) was loaded directly onto the guard column (Javelin BetaBasic C18) connected to a Waters Spherisorb ODS-2 analytical column (Keystone; 5 µm; 50 × 2 mm). The mobile phase consisted of 10 mm ammonium formate (pH 4.0):acetonitrile (18 : 82, v/v). Analysis was conducted on a SCIEX API 300 LC/MS/MS system using positive ion Turbo Ionspray with multiple reaction monitoring (MRM) ion detection. The almotriptan molecular ion (M + H) at 336 m z⁻¹ was monitored, along with its primary fragmentation ion at 201 m z⁻¹. The IS was monitored at 342 m z⁻¹ (M + H) and 207 m z⁻¹ (product ion).

Calibration standard responses were linear over the range of 0.5–200 ng ml⁻¹, using a weighted (1/concentration²) least squares linear regression model based on peak area ratios. Correlation coefficients, which measure the goodness of fit, were ≥ 0.9991. The lower limit of quantification for almotriptan was 0.5 ng ml⁻¹. Assay precision, expressed as the interday percentage coefficient of variation (CV) of the estimated concentrations of QC standards, was 2.3%, 2.9%, and 3.9%, respectively, for the 1.5, 50, and 150 ng ml⁻¹ QC pools.

Urine was collected from all subjects for both treatments on day 8. Subjects collected all urine voided into clean, disposable, pretared containers provided by the clinic. Each subject began urine collection at the time of awakening until just prior to dosing, when each subject voided his/her bladder immediately prior to dosing. Urine was then collected from 0–4, 4–8, 8–12, and 12–24 h after drug administration. Following each collection interval, the collected urine was well-mixed and the total volume recorded. A 20 ml aliquot of urine for each collection interval was frozen at −20 °C until analysis.

Urine samples were assayed for almotriptan concentrations using a validated, sensitive and specific h.p.l.c. assay. Using this method, almotriptan and the internal standard (PNU-181314, an analogue of almotriptan) were extracted from a 100 µl aliquot of urine using a Varian Prospekt 9200 automated in-line solid phase extraction system. The samples were centrifuged and injected onto cartridges (Varian Prospekt Bond Elute C2, 2 mm i.d.) that had been conditioned with methanol, followed by water. Loaded cartridges were washed with water:acetonitrile (70 : 30 v/v) and eluted with mobile phase [50 mm sodium phosphate (pH 4.0, with 0.1% triethylamine):acetonitrile (76 : 24 v/v)]. The effluent was loaded directly onto a Waters Spherisorb ODS-2 analytical column (Keystone; 5 µm; 150 × 4.6 mm). The mobile phase was run at a flow rate of 1.0 ml min⁻¹, and the analytes were detected by u.v. at 227 nm.

Calibration standard responses were linear over the range of 50–10 000 ng ml⁻¹, using a weighted (1/concentration²) least squares linear regression model based on peak height ratios. Correlation coefficients were ≥ 0.9971. The lower limit of quantification was 50 ng ml⁻¹. The interday CVs of the estimated concentrations of QC standards, were 2.8%, 2.7%, and 2.8%, respectively, for the 150, 2500, and 7500 ng ml⁻¹ QC pools; the CV was 0.3% for a two-fold dilution of the 7500 ng ml⁻¹ QC pool.

Data analysis

Pharmacokinetic parameters were calculated by the Clinical Pharmacokinetics Analysis Package, Version 1.0 [14], using noncompartmental methods [15]. The elimination rate constant (λ_z) was determined by linear regression of the terminal portion of the log concentration-time profile (which included 3–7 data points). Terminal half-life (t_½) was calculated as 0.693/λ_z. Area under the plasma concentration-time curve (AUC(0,∞)) was determined by trapezoidal rule up to the last time at which a measurable concentration was observed and extrapolated to infinity. Apparent oral clearance (CL_po) was calculated as Dose/AUC(0,∞). Maximal concentrations (C_max) and the time at which they occurred (t_max) were determined by inspection of the concentration-time profile. Renal clearance (CL_R) was calculated as:

where Ae is the cumulative renal excretion from 0 to 72 h.

Differences between treatments in pharmacokinetic parameters were assessed by analysis of variance (anova) for a crossover design. Blood pressure measures recorded on days 7 and 8 were analysed for treatment effects by anova for a crossover study at each time point. All statistical analyses were performed by SAS [16]. Using a CV of 8.47% for AUC(0,∞) (CV for residual error from anova), the actual power to detect a 20% difference in this parameter between treatments was 99.9% at an α level of 0.05.

Results

Pharmacokinetics

Mean plasma concentrations of almotriptan are depicted in Figure 1. It is clear that postpeak almotriptan concentrations were higher after concomitant administration of almotriptan and moclobemide than after almotriptan administration alone.

Figure 1.

Mean plasma concentrations of almotriptan following administration of 12.5 mg almotriptan in the presence (▪) and absence (□) of 150 mg moclobemide given twice daily.

Mean almotriptan pharmacokinetic parameters are summarized in Table 1. Mean almotriptan AUC(0,∞) was 37% higher and CL_po was 27% lower when almotriptan was administered with moclobemide than after almotriptan alone. Mean almotriptan half-life increased 24% following moclobemide administration. Mean V_z/F was 11% lower following coadministration of moclobemide. All of these differences were statistically significant. Mean C_max and t_max were unaffected by moclobemide administration. The fraction of the dose excreted in the urine as unchanged drug was significantly greater following coadministration of moclobemide, but renal clearance was unchanged.

Table 1.

Mean (± s.d.) pharmacokinetic parameters for almotriptan following the oral administration of 12.5 mg almotriptan in the presence and absence of 150 mg moclobemide given twice daily.

Parameters	Almotriptan+moclobemide	Almotriptan	Treatment P value anova
AUC(0,∞) (ng ml−1 h)	483	352	0.0001
	(99.9)	(75.4)
CLpo (l h−1)	26.6	36.6	0.0001
	(4.00)	(5.89)
Cmax (ng ml−1)	56.3	53.3	0.5061
	(14.2)	(12.4)
tmax (h)	2.71	2.13	0.1868
	(1.44)	(1.35)
λz (h−1)	0.17	0.21	0.0001
	(0.03)	(0.03)
t½ (h)	4.22	3.41	0.0002
	(0.78)	(0.45)
Ae (% of dose)	48.9	35.4	0.0001
	(8.03)	(4.36)
CLR (ml min−1)	216	215	0.8814
	(43.9)	(36.6)

Clinical assessments

Subjects in this study reported a number of adverse events of mild to moderate intensity; three subjects reported events prior to dosing. All events were nonserious and resolved with no residual effects. The most frequent adverse event was headache, occurring in four subjects.

No significant effects of treatment on oral temperature, pulse, or respirations were recorded. No significant effects of treatment on blood pressure were detected by repeated measures analysis of variance. No significant drug effects on the ECG or QTc intervals were observed.

Discussion

Sumatriptan and zolmitriptan are metabolised by monoamine oxidase type A (MAO-A) [11, 12]. Thus, the pharmacokinetics of these drugs may be altered by the coadministration of a MAO-A inhibitor, such as moclobemide. In the case of sumatriptan, AUC in plasma after subcutaneous administration is approximately doubled by moclobemide coadministration. Since sumatriptan is subject to a substantial first-pass effect after oral administration, the degree of interaction after oral administration is much greater. Zolmitriptan plasma concentrations are increased only about 25%, but the plasma concentrations of its active N-demethyl metabolite are increased approximately three fold. Concurrent administration of oral sumatriptan or zolmitriptan with MAO-A inhibitors is therefore contraindicated [13]. More recently, a substantial interaction between moclobemide and rizatriptan has also been reported, with the recommendation that rizatriptan not be used in patients receiving concomitant MAO inhibitors [17].

In vitro studies indicate that the indole acetic acid metabolite of almotriptan is formed by MAO-A. Analysis of data obtained following [¹⁴C]-almotriptan administration suggests that approximately 27% of the dose is excreted in the urine and faeces as the indole acetic acid metabolite or a conjugate thereof [6–7]. Therefore, it would be expected that systemic clearance of almotriptan via MAO-A would be approximately 27% of the total clearance of almotriptan in man. If this pathway was completely blocked, this would result in a 37% increase in almotriptan AUC. In the present study, almotriptan AUC was increased approximately 37% and clearance decreased 27% by the administration of moclobemide, an MAO-A inhibitor. CYP2D6 inhibition by moclobemide could also have contributed to the decrease in almotriptan clearance. However, fluoxetine, a potent CYP2D6 inhibitor, did not reduce almotriptan clearance [18]. The results of the present study thus show that the degree of interaction between almotriptan and an MAO-A inhibitor can be readily predicted from the results of in vitro experiments and the results of radiolabelled almotriptan disposition experiments in man.

Although moclobemide increased plasma concentrations of almotriptan, the degree of increase was modest relative to the interactions seen for other triptans. Additionally, the coadministration of these compounds appeared to be well-tolerated, and there was no evidence of cardiovascular side-effects. Due to the modest elevation of plasma almotriptan concentrations in the presence of moclobemide, no adjustment of the almotriptan dose is warranted.