Sumatriptan Succinate

SUMATRIPTAN SUCCINATE- sumatriptan succinate tablet
Cobalt Laboratories

DESCRIPTION

Sumatriptan tablets, USP contain sumatriptan (as the succinate), a selective 5-hydroxytryptamine1 receptor subtype agonist. Sumatriptan succinate is chemically designated as 3-[2-(dimethylamino)ethyl]-N-methyl-indole-5-methanesulfonamide succinate (1:1), and it has the following structure:

imitrex-tablets-chem-struc.jpg

The empirical formula is C14 H21 N3 O2 S•C4 H6 O4 , representing a molecular weight of 413.5. Sumatriptan succinate is a white to off-white powder that is readily soluble in water and in saline. Each sumatriptan tablet for oral administration contains 35, 70, or 140 mg of sumatriptan succinate equivalent to 25, 50, or 100 mg of sumatriptan, respectively. Each tablet also contains the following inactive ingredients: croscarmellose sodium, lactose anhydrous, magnesium stearate, and microcrystalline cellulose. Sumatriptan tablets (25 mg, 50 mg and 100 mg) comply with USP dissolution test 2.

CLINICAL PHARMACOLOGY

Mechanism of Action:

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 also 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.

Pharmacokinetics:

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 20-mg intranasal dose, respectively. The mean Cmax following a 6-mg 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 migraine-free period, but the Tmax is slightly later during the attack, approximately 2.5 hours compared to 2.0 hours. When given as a single dose, sumatriptan displays dose proportionality in its extent of absorption (area under the curve [AUC]) over the dose range of 25 to 200 mg, but the Cmax after 100 mg is approximately 25% less than expected (based on the 25-mg dose).

A food effect study involving administration of sumatriptan tablet 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.

Plasma protein binding is low (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 apparent volume of distribution is 2.4 L/kg.

The elimination half-life of sumatriptan is approximately 2.5 hours. Radiolabeled 14 C-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.

In vitro studies with human microsomes suggest that sumatriptan is metabolized by monoamine oxidase (MAO), predominantly the A isoenzyme, and inhibitors of that enzyme may alter sumatriptan pharmacokinetics to increase systemic exposure. No significant effect was seen with an MAO-B inhibitor (see CONTRAINDICATIONS, WARNINGS, and PRECAUTIONS: Drug Interactions).

Special Populations

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.

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 1 small study of 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 (see DOSAGE AND ADMINISTRATION).

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) (see PRECAUTIONS: Geriatric Use).

Gender:

In a study comparing females to males, no pharmacokinetic differences were observed between genders for AUC, Cmax , Tmax , and half-life.

Race:

The systemic clearance and Cmax of sumatriptan were similar in black (N = 34) and Caucasian (N = 38) healthy male subjects.

Drug Interactions

Monoamine Oxidase Inhibitors:

Treatment with MAO-A inhibitors generally leads to an increase of sumatriptan plasma levels (see CONTRAINDICATIONS and PRECAUTIONS).

Due to gut and hepatic metabolic first-pass effects, the increase of systemic exposure after coadministration of an MAO-A inhibitor with oral sumatriptan is greater than after coadministration of the monoamine oxidase inhibitors (MAOI) with subcutaneous sumatriptan. In a study of 14 healthy females, pretreatment with an MAO-A inhibitor decreased the clearance of subcutaneous sumatriptan. Under the conditions of this experiment, the result was a 2-fold increase in the area under the sumatriptan plasma concentration x time curve (AUC), corresponding to a 40% increase in elimination half-life. This interaction was not evident with an MAO-B inhibitor.

A small study 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.

CLINICAL STUDIES

The efficacy of sumatriptan tablets in the acute treatment of migraine headaches was demonstrated in 3, randomized, double-blind, placebo-controlled studies. Patients enrolled in these 3 studies were predominately female (87%) and Caucasian (97%), with a mean age of 40 years (range, 18 to 65 years). Patients were instructed to treat a moderate to severe headache. Headache response, defined as a reduction in headache severity from moderate or severe pain to mild or no pain, was assessed up to 4 hours after dosing. Associated symptoms such as nausea, photophobia, and phonophobia were also assessed. Maintenance of response was assessed for up to 24 hours postdose. A second dose of sumatriptan tablets or other medication was allowed 4 to 24 hours after the initial treatment for recurrent headache. Acetaminophen was offered to patients in Studies 2 and 3 beginning at 2 hours after initial treatment if the migraine pain had not improved or worsened. Additional medications were allowed 4 to 24 hours after the initial treatment for recurrent headache or as rescue in all 3 studies. The frequency and time to use of these additional treatments were also determined. In all studies, doses of 25, 50, and 100 mg were compared to placebo in the treatment of migraine attacks. In 1 study, doses of 25, 50, and 100 mg were also compared to each other.

In all 3 trials, the percentage of patients achieving headache response 2 and 4 hours after treatment was significantly greater among patients receiving sumatriptan tablets at all doses compared to those who received placebo. In 1 of the 3 studies, there was a statistically significant greater percentage of patients with headache response at 2 and 4 hours in the 50- or 100-mg group when compared to the 25-mg dose groups. There were no statistically significant differences between the 50- and 100-mg dose groups in any study. The results from the 3 controlled clinical trials are summarized in Table 1.

Comparisons of drug performance based upon results obtained in different clinical trials are never reliable. 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 response and the timing of response may be expected to vary considerably from study to study.

Table 1. Percentage of Patients With Headache Response (No or Mild Pain) 2 and 4 Hours Following Treatment

Placebo

2 hr 4 hr

Sumatriptan Tablets

25 mg

2 hr 4 hr

Sumatriptan Tablets

50 mg

2 hr 4 hr

Sumatriptan Tablets

100 mg

2 hr 4 hr

Study 1

27% 38%

52%* 67%*

61%*† 78%*†

62%*† 79%*†

(N = 94)

(N = 298)

(N = 296)

(N = 296)

Study 2

26% 38%

52%* 70%*

50%* 68%*

56%* 71%*

(N = 65)

(N = 66)

(N = 62)

(N = 66)

Study 3

17% 19%

52%* 65%*

54%* 72%*

57%* 78%*

(N = 47)

(N = 48)

(N = 46)

(N = 46)

* p<0.05 in comparison with placebo.

p<0.05 in comparison with 25 mg.

The estimated probability of achieving an initial headache response over the 4 hours following treatment is depicted in Figure 1.

imitrex-tablets-fig1.jpg
(click image for full-size original)

Figure 1. Estimated Probability of Achieving Initial Headache Response Within 240 Minutes*

* The figure shows the probability over time of obtaining headache response (no or mild pain) following treatment with sumatriptan. The averages displayed are based on pooled data from the 3 clinical controlled trials providing evidence of efficacy. Kaplan-Meier plot with patients not achieving response and/or taking rescue within 240 minutes censored to 240 minutes.

For patients with migraine-associated nausea, photophobia, and/or phonophobia at baseline, there was a lower incidence of these symptoms at 2 hours (Study 1) and at 4 hours (Studies 1, 2, and 3) following administration of sumatriptan tablets compared to placebo.

As early as 2 hours in Studies 2 and 3 or 4 hours in Study 1, through 24 hours following the initial dose of study treatment, patients were allowed to use additional treatment for pain relief in the form of a second dose of study treatment or other medication. The estimated probability of patients taking a second dose or other medication for migraine over the 24 hours following the initial dose of study treatment is summarized in Figure 2.

imitrex-tablets-fig2.jpg
(click image for full-size original)

Figure 2. The Estimated Probability of Patients Taking a Second Dose or Other Medication for Migraine Over the 24 Hours Following the Initial Dose of Study Treatment*

* Kaplan-Meier plot based on data obtained in the 3 clinical controlled trials providing evidence of efficacy with patients not using additional treatments censored to 24 hours. Plot also includes patients who had no response to the initial dose. No remedication was allowed within 2 hours postdose.

There is evidence that doses above 50 mg do not provide a greater effect than 50 mg. There was no evidence to suggest that treatment with sumatriptan was associated with an increase in the severity of recurrent headaches. The efficacy of sumatriptan tablets was unaffected by presence of aura; duration of headache prior to treatment; gender, age, or weight of the patient; relationship to menses; or concomitant use of common migraine prophylactic drugs (e.g., beta-blockers, calcium channel blockers, tricyclic antidepressants). There were insufficient data to assess the impact of race on efficacy.

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