Zolmitriptan (Page 4 of 7)

11 DESCRIPTION

Zolmitriptan tablets, USP contain zolmitriptan, which is a selective 5-hydroxytryptamine_1B/1D (5-HT_1B/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:

The molecular formula is C₁₆ H₂₁ N₃ O₂ , representing a molecular weight of 287.36. Zolmitriptan is a white to off-white powder that is readily soluble in water.
Zolmitriptan tablets, USP are available as 2.5 mg (yellow and functionally-score) and 5 mg (pink, not scored) film-coated tablets for oral administration. The film-coated tablets contain anhydrous lactose, colloidal silicon dioxide, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, sodium starch glycolate, and titanium dioxide. In addition, the 2.5 mg tablets contain yellow iron oxide and the 5 mg tablets contain red iron oxide.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Zolmitriptan binds with high affinity to human recombinant 5-HT_1D and 5-HT_1B receptors, and moderate affinity for 5-HT_1A receptors. The N-desmethyl metabolite also has high affinity for 5-HT_1B/1D and moderate affinity for 5-HT_1A 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-HT_1B/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 C_max of zolmitriptan are similar following administration of zolmitriptan tablets and Zolmitriptan Orally Disintegrating Tablets, but the T_max is somewhat later with Zolmitriptan Orally Disintegrating Tablets, with a median T_max of 3 hours for Zolmitriptan Orally Disintegrating Tablet compared with 1.5 hours for the zolmitriptan tablet. The AUC, C_max , and T_max for the active N-desmethyl metabolite are similar for the two formulations.
During a moderate to severe migraine attack, mean AUC_0-4 and C_max for zolmitriptan, dosed as a zolmitriptan tablet, were decreased by 40% and 25%, respectively, and mean T_max 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 L/kg. Plasma protein binding of zolmitriptan is 25% over the concentration range of 10 to 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 5-HT_1B/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.
Specific Populations

Hepatic Impairment

In patients with severe hepatic impairment, the mean C_max , T_max , and AUC_0-∞ 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), 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 to 76 years) was similar to those in younger non-migraineur volunteers (age 18 to 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 C_max and AUC for zolmitriptan and a 3-fold increase in the C_max 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), 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

C_max and AUC of zolmitriptan were increased 1.5-fold after one week of dosing with propranolol (160 mg/day). C_max 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 T_max 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 C_max and AUC of zolmitriptan were increased by 30% and 50%, respectively, and T_max 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.