Sumatriptan pharmacokinetics and molecular data

Pharmacokinetics and molecular data
Mechanism Pharmacokinetics Special populations
 * Renal impairment
 * Hepatic impairment
 * Age
 * Race

Mechanism
Sumatriptan is an agonist for a vascular 5-hydroxytryptamine1 receptor subtype (probably a member of the 5-HT1D family) having only a weak affinity for 5-HT1A, 5-HT5A, and 5-HT7 receptors and no significant affinity (as measured using standard radioligand binding assays) or pharmacological activity at 5-HT2, 5-HT3, or 5-HT4 receptor subtypes or at alpha1-, alpha2-, or beta-adrenergic; dopamine1; dopamine2; muscarinic; or benzodiazepine receptors. The vascular 5-HT1 receptor subtype that sumatriptan activates is present on cranial arteries in both dog and primate, on the human basilar artery, and in the vasculature of human dura mater and mediates vasoconstriction. This action in humans correlates with the relief of migraine headache. In addition to causing vasoconstriction, experimental data from animal studies show that sumatriptan also activates 5-HT1 receptors on peripheral terminals of the trigeminal nerve innervating cranial blood vessels. Such an action may contribute to the antimigrainous effect of sumatriptan in humans. In the anesthetized dog, sumatriptan selectively reduces the carotid arterial blood flow with little or no effect on arterial blood pressure or total peripheral resistance. In the cat, sumatriptan selectively constricts the carotid arteriovenous anastomoses while having little effect on blood flow or resistance in cerebral or extracerebral tissues. Return to top

Pharmacokinetics
In a study of 20 female volunteers, the mean maximum concentration following a 5- and 20-mg intranasal dose was 5 and 16 ng/mL, respectively. The mean Cmax following a 6-mg subcutaneous injection is 71 ng/mL (range, 49 to 110 ng/mL). The mean Cmax is 18 ng/mL (range, 7 to 47 ng/mL) following oral dosing with 25 mg and 51 ng/mL (range, 28 to 100 ng/mL) following oral dosing with 100 mg of sumatriptan. In a study of 24 male volunteers, the bioavailability relative to subcutaneous injection was low, approximately 17%, primarily due to presystemic metabolism and partly due to incomplete absorption. 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, but would be expected to be minor, given the low rate of protein binding. The mean volume of distribution after subcutaneous dosing is 2.7 L/kg and the total plasma clearance is approximately 1,200 mL/min. The elimination half-life of sumatriptan administered as a nasal spray is approximately 2 hours, similar to the half-life seen after subcutaneous injection. Only 3% of the dose is excreted in the urine as unchanged sumatriptan; 42% of the dose is excreted as the major metabolite, the indole acetic acid analogue of sumatriptan. Clinical and pharmacokinetic data indicate that administration of two 5-mg doses, 1 dose in each nostril, is equivalent to administration of a single 10-mg dose in 1 nostril. Return to top

Renal impairment
The effect of renal impairment on the pharmacokinetics of sumatriptan has not been examined, but little clinical effect would be expected as sumatriptan is largely metabolized to an inactive substance. Return to top

Hepatic impairment
The effect of hepatic disease on the pharmacokinetics of subcutaneously and orally administered sumatriptan has been evaluated, but the intranasal dosage form has not been studied in hepatic impairment. There were no statistically significant differences in the pharmacokinetics of subcutaneously administered sumatriptan in hepatically impaired patients compared to healthy controls. However, the liver plays an important role in the presystemic clearance of orally administered sumatriptan. In 1 small study involving oral sumatriptan in hepatically impaired patients (N = 8) matched for sex, age, and weight with healthy subjects, 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 bioavailability of nasally absorbed sumatriptan following intranasal administration, which would not undergo first-pass metabolism, should not be altered in hepatically impaired patients. The bioavailability of the swallowed portion of the intranasal sumatriptan dose has not been determined, but would be increased in these patients. The swallowed intranasal dose is small, however, compared to the usual oral dose, so that its impact should be minimal. Return to top

Age
The pharmacokinetics of oral sumatriptan in the elderly (mean age, 72 years; 2 males and 4 females) and in patients with migraine (mean age, 38 years; 25 males and 155 females) were similar to that in healthy male subjects (mean age, 30 years). Intranasal sumatriptan has not been evaluated for age differences. Return to top

Race
The systemic clearance and Cmax of sumatriptan were similar in black (n = 34) and Caucasian (n = 38) healthy male subjects. Intranasal sumatriptan has not been evaluated for race differences. Return to top