IMITREX tablet clinical pharmacology

# Clinical Pharmacology

### Mechanism of Action
Sumatriptan binds with high affinity to human cloned 5HT1B/1D receptors. Sumatriptan presumably exerts its therapeutic effects in the treatment of migraine headache through agonist effects at the 5HT1B/1D receptors on intracranial blood vessels and sensory nerves of the trigeminal system, which result in cranial vessel constriction and inhibition of proinflammatory neuropeptide release.

### Pharmacodynamics
Blood Pressure: Significant elevation in blood pressure, including hypertensive crisis, has been reported in patients with and without a history of hypertension .
Peripheral (Small) Arteries: In healthy volunteers (N = 18), a trial evaluating the effects of sumatriptan on peripheral (small vessel) arterial reactivity failed to detect a clinically significant increase in peripheral resistance.
Heart Rate: Transient increases in blood pressure observed in some patients in clinical trials carried out during sumatriptans development as a treatment for migraine were not accompanied by any clinically significant changes in heart rate.

### Pharmacokinetics
Absorption and Bioavailability: The mean maximum concentration following oral dosing with 25 mg is 18 ng/mL (range: 7 to 47 ng/mL) and 51 ng/mL (range: 28 to 100 ng/mL) following oral dosing with 100 mg of sumatriptan. This compares with a Cmax of 5 and 16 ng/mL following dosing with a 5- and 20mg intranasal dose, respectively. The mean Cmax following a 6mg subcutaneous injection is 71 ng/mL (range: 49 to 110 ng/mL). The bioavailability is approximately 15%, primarily due to presystemic metabolism and partly due to incomplete absorption. The Cmax is similar during a migraine attack and during a migrainefree period, but the Tmax is slightly later during the attack, approximately 2.5 hours compared with 2.0 hours. When given as a single dose, sumatriptan displays dose proportionality in its extent of absorption (area under the curve ) over the dose range of 25 to 200 mg, but the Cmax after 100 mg is approximately 25% less than expected (based on the 25mg dose).
A food effect trial involving administration of IMITREX Tablets 100 mg to healthy volunteers under fasting conditions and with a high	fat meal indicated that the Cmax	 and AUC were increased by 15% and 12%, respectively, when administered in the fed state.
Distribution: Protein binding, determined by equilibrium dialysis over the concentration range of 10 to 1,000 ng/mL is low, approximately 14% to 21%. The effect of sumatriptan on the protein binding of other drugs has not been evaluated. The apparent volume of distribution is 2.7 L/kg.
Metabolism: In vitro studies with human microsomes suggest that sumatriptan is metabolized by MAO, predominantly the A isoenzyme. Most of a radiolabeled dose of sumatriptan excreted in the urine is the major metabolite indole acetic acid (IAA) or the IAA glucuronide, both of which are inactive.
Elimination: The elimination half-life of sumatriptan is approximately 2.5 hours. Radiolabeled 14C-sumatriptan administered orally is largely renally excreted (about 60%) with about 40% found in the feces. Most of the radiolabeled compound excreted in the urine is the major metabolite, indole acetic acid (IAA), which is inactive, or the IAA glucuronide. Only 3% of the dose can be recovered as unchanged sumatriptan.
Special Populations: Age: The pharmacokinetics of sumatriptan in the elderly (mean age: 72 years, 2 males and 4 females) and in subjects with migraine (mean age: 38 years, 25 males and 155 females) were similar to that in healthy male subjects (mean age: 30 years).
Renal Impairment: The effect of renal impairment on the pharmacokinetics of sumatriptan has not been examined.
Hepatic Impairment: The liver plays an important role in the presystemic clearance of orally administered sumatriptan. Accordingly, the bioavailability of sumatriptan following oral administration may be markedly increased in patients with liver disease. In one small trial of patients with moderate liver impairment (n = 8) matched for sex, age, and weight with healthy subjects (n = 8), the hepatically-impaired patients had an approximately 70% increase in AUC and Cmax and a Tmax 40 minutes earlier compared to the healthy subjects.
The pharmacokinetics of sumatriptan in patients with severe hepatic impairment has not been studied. The use of IMITREX Tablets in this population is contraindicated .
Gender:In a trial comparing females to males, no pharmacokinetic differences were observed between genders for AUC, Cmax, Tmax, and halflife.
Race: The systemic clearance and Cmax of subcutaneous sumatriptan were similar in black (n = 34) and Caucasian (n = 38) healthy male subjects. Oral sumatriptan has not been evaluated for race differences.
Drug Interaction Studies: Monoamine Oxidase-A Inhibitors:Treatment with MAO-A inhibitors generally leads to an increase of sumatriptan plasma levels .
Due to gut and hepatic metabolic first-pass effects, the increase of systemic exposure after co-administration of an MAO-A inhibitor with oral sumatriptan is greater than after co-administration of the MAO inhibitors with subcutaneous sumatriptan.
In a trial of 14 healthy females, pretreatment with an MAO-A inhibitor decreased the clearance of subcutaneous sumatriptan, resulting in a 2-fold increase in the area under the sumatriptan plasma concentration-time curve (AUC), corresponding to a 40% increase in elimination half-life.
A small trial evaluating the effect of pretreatment with an MAO-A inhibitor on the bioavailability from a 25-mg oral sumatriptan tablet resulted in an approximately 7-fold increase in systemic exposure.
Alcohol: Alcohol consumed 30 minutes prior to sumatriptan ingestion had no effect on the pharmacokinetics of sumatriptan.