Axert (Almotriptan Malate) - Description and Clinical Pharmacology

PRESCRIBING INFORMATION

DESCRIPTION

AXERT^® (almotriptan malate) Tablets contain almotriptan malate, a selective 5-hydroxytryptamine_1B/1D (5‑HT_1B/1D) receptor agonist. Almotriptan malate is chemically designated as 1-[[[3-[2-(Dimethylamino)ethyl]-1H-indol-5-yl]methyl]sulfonyl]pyrrolidine (±)-hydroxybutanedioate (1:1), and its structural formula is:

Its empirical formula is C₁₇H₂₅N₃O₂S-C₄H₆O₅, representing a molecular weight of 469.56. Almotriptan is a white to slightly yellow crystalline powder that is soluble in water. AXERT^® for oral administration contains almotriptan malate equivalent to 6.25 or 12.5 mg of almotriptan. Each compressed tablet contains the following inactive ingredients: mannitol, cellulose, povidone, sodium starch glycolate, sodium stearyl fumarate, titanium dioxide, hypromellose, polyethylene glycol, propylene glycol, iron oxide (6.25 mg only), FD&C Blue No. 2 (12.5 mg only), and carnauba wax.

CLINICAL PHARMACOLOGY

Mechanism of Action

Almotriptan binds with high affinity to 5-HT_1D, 5-HT_1B, and 5-HT_1F receptors. Almotriptan has weak affinity for 5-HT_1A and 5-HT₇ receptors, but has no significant affinity or pharmacological activity at 5-HT₂, 5-HT₃, 5-HT₄, 5-HT₆; alpha or beta adrenergic; adenosine (A₁, A₂); angiotensin (AT₁, AT₂); dopamine (D₁, D₂); endothelin (ET_A, ET_B); or tachykinin (NK₁, NK₂, NK₃) binding sites.

Current theories on the etiology of migraine headache suggest that symptoms are due to local cranial vasodilatation and/or to the release of vasoactive and pro-inflammatory peptides from sensory nerve endings in an activated trigeminal system. The therapeutic activity of almotriptan in migraine can most likely be attributed to agonist effects at 5-HT_1B/1D receptors on the extracerebral, intracranial blood vessels that become dilated during a migraine attack, and on nerve terminals in the trigeminal system. Activation of these receptors results in cranial vessel constriction, inhibition of neuropeptide release, and reduced transmission in trigeminal pain pathways.

Pharmacokinetics

General

Almotriptan is well absorbed after oral administration (absolute bioavailability about 70%) with peak plasma levels 1 to 3 hours after administration; food does not affect pharmacokinetics. Almotriptan has a mean half-life of 3 to 4 hours. It is eliminated primarily by renal excretion (about 75% of the oral dose). Almotriptan is minimally protein bound (approximately 35%) and the mean apparent volume of distribution is approximately 180 to 200 liters.

Metabolism and Excretion

Almotriptan is metabolized by one minor and two major pathways. Monoamine oxidase (MAO)-mediated oxidative deamination (approximately 27% of the dose), and cytochrome P450-mediated oxidation (approximately 12% of the dose) are the major routes of metabolism, while flavin monooxygenase is the minor route. MAO-A is responsible for the formation of the indoleacetic acid metabolite, whereas cytochrome P450 (3A4 and 2D6) catalyzes the hydroxylation of the pyrrolidine ring to an intermediate that is further oxidized by aldehyde dehydrogenase to the gamma-aminobutyric acid derivative. Both metabolites are inactive.

Approximately 40% of an administered dose is excreted unchanged in urine. Renal clearance exceeds the glomerular filtration rate by approximately 3-fold, indicating an active mechanism. Approximately 13% of the administered dose is excreted via feces, both unchanged and metabolized.

Special Populations

Geriatric

Renal and total clearance, and amount of drug excreted in the urine were lower in elderly healthy volunteers (age 65 to 76 years) than in younger healthy volunteers (age 19 to 34 years), resulting in longer terminal half-life (3.7 h vs. 3.2 h) and a 25% higher area under the plasma concentration-time curve in the elderly subjects.  The differences, however, do not appear to be clinically significant.

Pediatric

The pharmacokinetics of almotriptan in pediatric patients have not been evaluated.

Gender

No significant gender differences have been observed in pharmacokinetic parameters.

Race

No significant differences have been observed in pharmacokinetic parameters between Caucasian and African-American volunteers.

Hepatic Impairment

The pharmacokinetics of almotriptan have not been assessed in this population. Based on the known mechanisms of clearance of almotriptan, the maximum decrease expected in almotriptan clearance due to hepatic impairment would be 60% (see DOSAGE AND ADMINISTRATION).

Renal Impairment

The clearance of almotriptan was approximately 65% lower in patients with severe renal impairment (Cl/F=19.8 L/h; creatinine clearance between 10 and 30 mL/min) and approximately 40% lower in patients with moderate renal impairment (Cl/F=34.2 L/h; creatinine clearance between 31 and 71 mL/min) than in healthy volunteers (Cl/F= 57 L/h). Maximal plasma concentrations of almotriptan increased by approximately 80% in these patients (see DOSAGE AND ADMINISTRATION).

Drug Interactions

(see also PRECAUTIONS, Drug Interactions)

All drug interaction studies were performed in healthy volunteers using a single 12.5 mg dose of almotriptan and multiple doses of the other drug.

Monoamine Oxidase Inhibitors

Coadministration of almotriptan and moclobemide (150 mg b.i.d. for 8 days) resulted in a 27% decrease in almotriptan clearance.

Propanolol

Coadministration of almotriptan and propranolol (80 mg b.i.d. for 7 days) resulted in no significant changes in the pharmacokinetics of almotriptan.

Selective Serotonin Reuptake Inhibitors

Coadministration of almotriptan and fluoxetine (60 mg daily for 8 days), a potent inhibitor of CYP4502D6, had no effect on almotriptan clearance, but maximal concentrations of almotriptan were increased 18%. This difference is not clinically significant.

Verapamil

Coadministration of almotriptan and verapamil (120 mg sustained release tablets b.i.d for 7 days), an inhibitor of CYP3A4, resulted in a 20% increase in the area under the plasma concentration-time curve, and in a 24% increase in maximal plasma concentrations of almotriptan. Neither of these changes is clinically significant.

Ketoconazole and Other Potent CYP3A4 Inhibitors

Coadministration of almotriptan and the potent CYP3A4 inhibitor ketoconazole (400 mg qd for 3 days) resulted in an approximately 60% increase in the area under the plasma concentration-time curve and maximal plasma concentrations of almotriptan. Although the interaction between almotriptan and other potent CYP3A4 inhibitors (e.g., itraconazole, ritonavir, and erythromycin) has not been studied, increased exposures to almotriptan may be expected when almotriptan is used concomitantly with these medications.

CLINICAL STUDIES

The efficacy of AXERT^® (almotriptan malate) Tablets was established in 3 multi-center, randomized, double-blind, placebo-controlled European trials. Patients enrolled in these studies were primarily female (86%) and Caucasian (more than 98%), with a mean age of 41 years (range of 18 to 72). Patients were instructed to treat a moderate to severe migraine headache. Two hours after taking one dose of study medication, patients evaluated their headache pain. If the pain had not decreased in severity to mild or to no pain, the patient was allowed to take an escape medication. If the pain had decreased to mild or to no pain at 2 hours but subsequently increased in severity between 2 and 24 hours, it was considered a relapse and the patient was instructed to take a second dose of study medication. Associated symptoms of nausea, vomiting, photophobia, and phonophobia were also evaluated.

In these studies, the percentage of patients achieving a response (mild or no pain) 2 hours after treatment was significantly greater in patients who received either AXERT^® 6.25 mg or 12.5 mg, compared with those who received placebo. A higher percentage of patients reported pain relief after treatment with the 12.5 mg dose than with the 6.25 mg dose. Doses greater than 12.5 mg did not lead to significantly better response. These results are summarized in Table 1.

Table 1. Response Rates 2 Hours Following Treatment of Initial Headache

	Placebo	AXERT® 6.25 mg	AXERT® 12.5 mg
Study 1	33.8% (n = 80)	55.4%p value 0.002 in comparison with placebo (n = 166)	58.5% 1 (n = 164)
Study 2	40.0% (n = 95)	---	57.1%p value 0.008 in comparison with placebo (n =175)
Study 3	33.0% (n = 176)	55.6% (n = 360)	64.9% (n = 370)

These results cannot be validly compared with results of anti-migraine treatments in other studies. Because studies are conducted at different times, with different samples of patients, by different investigators, employing different criteria and/or different interpretations of the same criteria, under different conditions (dose, dosing regimen, etc.), quantitative estimates of treatment responses and the timing of response may be expected to vary considerably from study to study.

Theestimated probability of achieving pain relief within 2 hours following initial treatment with AXERT^® is shown in Figure 1.

Figure 1. Estimated Probability of Achieving an Initial Headache Response (mild or no pain) in 2 Hours

This Kaplan-Meier plot is based on data obtained in the three placebo-controlled clinical trials that provided evidence of efficacy (Studies 1, 2, and 3). Patients not achieving pain relief by 2 hours were censored at 2 hours.

For patients with migraine-associated photophobia, phonophobia, nausea, and vomiting at baseline, there was a decreased incidence of these symptoms following administration of AXERT^® compared with placebo.

Two to 24 hours following the initial dose of study medication, patients were allowed to take an escape medication or a second dose of study medication for pain response. The estimated probability of patients taking escape medication or a second dose of study medication over the 24 hours following the initial dose of study medication is shown in Figure 2.

Figure 2. Estimated Probability of Patients Taking Escape Medication or a Second Dose of Study Medication Over the 24 Hours Following the Initial Dose of Study Treatment

This Kaplan-Meier plot is based on data obtained in the three placebo-controlled trials that provided evidence of efficacy (Studies 1, 2, and 3). Patients not using additional treatment were censored at 24 hours. Remedication was not allowed within 2 hours after the initial dose of AXERT^®.

The efficacy of AXERT^® was unaffected by the presence of aura; by gender, weight, or age of the patient; or by concomitant use of common migraine prophylactic drugs (e.g., beta-blockers, calcium channel blockers, tricyclic antidepressants), or oral contraceptives. There were insufficient data to assess the effect of race on efficacy.