Zolmitriptan OD (Page 4 of 7)

11 DESCRIPTION

Zolmitriptan orally disintegrating tablets contain zolmitriptan, which is a selective 5-hydroxytryptamine1B/1D (5-HT1B/1D ) receptor agonist. Zolmitriptan is chemically designated as (S)-4-[[3-[2-(dimethylamino)ethyl]-1H-indol-5-yl]methyl]-2-oxazolidinone and has the following chemical structure:

zolmitriptan structure
(click image for full-size original)

The molecular formula is C­16 ­H­21 ­N­3 ­O­­2 ­, representing a molecular weight of 287.36. Zolmitriptan is white to cream colored crystalline powder that is freely soluble in methanol, slightly soluble in ethyl acetate and very slightly soluble in water.
Zolmitriptan orally disintegrating tablets are available for oral administration as 2.5 mg and 5 mg, white colored, round shaped, flat faced, beveled edged tablets. Each orally disintegrating tablet contains acesulfame potassium, aminomethacrylate copolymer, colloidal silicon dioxide, crospovidone, low-substituted hydroxypropyl cellulose, magnesium aluminometasilicate, magnesium stearate, mannitol, peppermint flavor, sodium lauryl sulfate and talc.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Zolmitriptan binds with high affinity to human recombinant 5­-HT1D and 5-HT1B receptors, and moderate affinity for 5-HT1A receptors. The N-desmethyl metabolite also has high affinity for 5-HT1B/1D and moderate affinity for 5-HT1A receptors.
Migraines are likely due to local cranial vasodilatation and/or to the release of sensory neuropeptides (vasoactive intestinal peptide, substance P and calcitonin gene-related peptide) through nerve endings in the trigeminal system. The therapeutic activity of zolmitriptan for the treatment of migraine headache is thought to be due to the agonist effects at the 5-HT1B/1D receptors on intracranial blood vessels (including the arterio-venous anastomoses) and sensory nerves of the trigeminal system which result in cranial vessel constriction and inhibition of pro-inflammatory neuropeptide release.

12.3 Pharmacokinetics

Absorption, Distribution, Metabolism, and Excretion
Absorption
Zolmitriptan is well absorbed after oral administration for both zolmitriptan tablets and the zolmitriptan orally disintegrating tablets. Zolmitriptan displays linear kinetics over the dose range of 2.5 to 50 mg.
The AUC and Cmax of zolmitriptan are similar following administration of zolmitriptan tablets and zolmitriptan orally disintegrating tablets, but the Tmax is somewhat later with zolmitriptan orally disintegrating tablets, with a median Tmax of 3 hours for zolmitriptan orally disintegrating tablets compared with 1.5 hours for the zolmitriptan tablet. The AUC, Cmax , and Tmax for the active N-desmethyl metabolite are similar for the two formulations.

During a moderate to severe migraine attack, mean AUC0-4 and Cmax for zolmitriptan, dosed as a zolmitriptan tablet, were decreased by 40% and 25%, respectively, and mean Tmax was delayed by one-half hour compared to the same patients during a migraine free period.
Food has no significant effect on the bioavailability of zolmitriptan. No accumulation occurred on multiple dosing.

Distribution
Mean absolute bioavailability is approximately 40%. The mean apparent volume of distribution is 7.0 L/kg. Plasma protein binding of zolmitriptan is 25% over the concentration range of 10-1000 ng/mL.
Metabolism
Zolmitriptan is converted to an active N-desmethyl metabolite; the metabolite concentrations are about two-thirds that of zolmitriptan. Because the 5HT1B/1D potency of the metabolite is 2 to 6 times that of the parent compound, the metabolite may contribute a substantial portion of the overall effect after zolmitriptan administration.

Excretion
Total radioactivity recovered in urine and feces was 65% and 30% of the administered dose, respectively. About 8% of the dose was recovered in the urine as unchanged zolmitriptan. Indole acetic acid metabolite accounted for 31% of the dose, followed by N-oxide (7%) and N-desmethyl (4%) metabolites. The indole acetic acid and N-oxide metabolites are inactive.
Mean total plasma clearance is 31.5 mL/min/kg, of which one-sixth is renal clearance. The renal clearance is greater than the glomerular filtration rate suggesting renal tubular secretion.

Special Populations
Hepatic Impairment
In patients with severe hepatic impairment, the mean Cmax , Tmax , and AUC0-∞ of zolmitriptan were increased 1.5-fold, 2-fold (2 vs. 4 hours), and 3-fold, respectively, compared to subjects with normal hepatic function. Seven out of 27 patients experienced 20 to 80 mm Hg elevations in systolic and/or diastolic blood pressure after a 10 mg zolmitriptan dose. Adjust the zolmitriptan dose in patients with moderate or severe hepatic impairment [see Dosage and Administration (2.3) and Use in Specific Populations (8.6)].

Renal Impairment
Clearance of zolmitriptan was reduced by 25% in patients with severe renal impairment (Clcr ≥ 5 ≤ 25 mL/min) compared to subjects with normal renal function (Clcr ≥ 70 mL/min); no significant change in clearance was observed in patients with moderate renal impairment (Clcr ≥ 26 ≤ 50 mL/min).
Age
Zolmitriptan pharmacokinetics in healthy elderly non-migraineur volunteers (age 65–76 years) was similar to those in younger non-migraineur volunteers (age 18-39 years).

Sex
Mean plasma concentrations of zolmitriptan were up to 1.5-fold higher in females than males.

Race
Retrospective analysis of pharmacokinetic data between Japanese and Caucasians revealed no significant differences.

Hypertensive Patients
No differences in the pharmacokinetics of zolmitriptan or its effects on blood pressure were seen in mild to moderate hypertensive volunteers compared with normotensive controls.

Drug Interaction Studies
All drug interaction studies were performed in healthy volunteers using a single 10 mg dose of zolmitriptan and a single dose of the other drug except where otherwise noted.

MAO Inhibitors
Following one week of administration of moclobemide (150 mg twice daily), a specific MAO-A inhibitor, there was an increase of about 25% in both Cmax and AUC for zolmitriptan and a 3-fold increase in the Cmax and AUC of the active N­-desmethyl metabolite of zolmitriptan. MAO inhibitors are contraindicated in zolmitriptan-treated patients [see Contraindications(4), Warnings and Precautions (5.7), and Drug Interactions (7.2, 7.4)].
Selegiline, a selective MAO-B inhibitor, at a dose of 10 mg/day for 1 week, had no effect on the pharmacokinetics of zolmitriptan and its metabolite.

Cimetidine
Following the administration of cimetidine, the half-life and AUC of zolmitriptan (5 mg dose), and its active metabolite, were approximately doubled [see Dosage and Administration (2.4), Drug Interactions (7.5)].

Fluoxetine
The pharmacokinetics of zolmitriptan, as well as its effect on blood pressure, were unaffected by 4 weeks of pretreatment with oral fluoxetine (20 mg/day).

Propranolol
Cmax and AUC of zolmitriptan were increased 1.5-fold after one week of dosing with propranolol (160 mg/day). Cmax and AUC of the N-desmethyl metabolite were reduced by 30% and 15%, respectively. There were no changes in blood pressure or pulse rate following administration of propranolol with zolmitriptan.

Acetaminophen
A single 1 gram dose of acetaminophen did not alter the pharmacokinetics of zolmitriptan and its N-desmethyl metabolite. However, zolmitriptan administration delayed the Tmax of acetaminophen by one hour.

Metoclopramide
A single 10 mg dose of metoclopramide had no effect on the pharmacokinetics of zolmitriptan or its metabolites.

Oral Contraceptives
Retrospective analysis of pharmacokinetic data across studies indicated that mean Cmax and AUC of zolmitriptan were increased by 30% and 50%, respectively, and Tmax was delayed by one-half hour in women taking oral contraceptives. The effect of zolmitriptan on the pharmacokinetics of oral contraceptives has not been studied.

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