Inclusion Criteria:

• Subject is >10 years of age and <17 years of age at the informed consent and the Randomization Visit.
• Subject has migraine with or without aura (ICHD-II criteria, 1.1 or 1.2.1). A minimum of a six month history of migraine prior to entry into the study is required.
• Subject has a history of at least two, but no more than eight, attacks per month for the two months prior to entry into the study.
• All migraine attacks associated with 3 or more pain on a 5-grade scale should last a minimum of three hours for the two months prior to entry into the study.
• Subject has shown nonresponse to at least one NSAIDs or acetaminophen for the two months prior to entry into the study.
• Subject is able to distinguish migraine from other headaches (e.g., tension-type headache).
• Subject is able to read, comprehend, and complete subject diaries.
• Males or female subjects. Female subjects are eligible for participation in the study if they are one of the following
• Females of non-childbearing potential (i.e., physiologically incapable of becoming pregnant or have undergone female sterilization)
• Females of childbearing potential, and who have a negative pregnancy test at the Screening Visit, and agree to use one of the following GlaxoSmithKline (GSK)-specified highly effective methods for avoiding pregnancy:
• Abstinence
• Oral Contraceptive, either combined or progestogen alone
• Male partner sterilization (vasectomy with documentation of azoospermia) prior to the female subject's entry into the study, and this male is the sole partner for that subject)
• Double barrier method: condom or occlusive cap (diaphragm or cervical/vault caps) plus spermicidal agent (foam/gel/film/cream/suppository)
• Subject's parent or legal guardian is willing and able to provide informed consent prior to subject entry into the study.
• Subject is willing and able to provide informed assent prior to entry into the study.
• Subjects considered for enrolment must have a QTc (either QTc B (Bazett's correction) or QTc F (Fridericia's correction)) <450msec at the Screening Visit, with the exception of subjects with bundle branch block (for whom either QTc B or QTc F must be <480msec).

Note: For the purposes of these criteria, QTc B is defined as (QT interval msec) / (square root of RR interval seconds); and QTc F is defined as (QT interval msec) / (cube root of RR interval seconds).)

• Liver function test at the Screening Visit: AST and ALT <2xULN; alkaline phosphatase and total bilirubin <1.5xULN (isolated bilirubin >1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin <35%)

Exclusion Criteria:

• Subject is < 30 kg.
• Subject has 15 or more headache days per month in total (migraine, probable migraine, or tension-type). Subject has retinal (ICHD-II 1.4), basilar (ICHD-II 1.2.6), hemiplegic (ICHD-II 1.2.4 or 1.2.5), or Ophthalmoplegic migraine (ICHD-II 13.17). Subject has secondary headaches.
• Subject has a history of cerebrovascular disease or ischemic cerebrovascular disease.
• Subject has a history of myocardial infarction.
• Subject has uncontrolled hypertension.
• Subject has symptoms or signs of ischemic cardiac syndromes.
• Subject has variant angina.
• Subject has evidence of a peripheral vascular syndrome.
• Subject has evidence or history of epilepsy or structural brain lesions which lower the convulsive threshold, or has been treated with an antiepileptic drug for seizure control.
• Subject has a history of impaired hepatic or renal function that, in the investigator (or subinvestigator)'s opinion, contraindicates participation in this study. Subject has unstable liver disease (as defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, esophageal or gastric varices or persistent jaundice). Subject has cirrhosis. Subject has known biliary abnormalities (with the exception of Gilberts's syndrome or asymptomatic gallstones).
• Subject has hypersensitivity, allergy, intolerance, or contraindication to the use of any triptan (including all sumatriptan preparations) or sulfonamide compounds.
• Subject has used an ergot medication in the previous three months for migraine prophylaxis or is taking a medication that is not stabilized (i.e., change of dose within the past 2 months) for either chronic or intermittent migraine prophylaxis.
• Subject has taken, or plans to take, a monoamine oxidase inhibitor (MAOI) anytime within the two weeks prior to entry into the study.
• Subject has evidence of psychotropic, alcohol, or substance abuse within the last year.
• Subject has participated in any investigational drug trial within the previous 3 months or plans to participate in another study at any time during this study.
• Subject has any concurrent medical or psychiatric condition which, in the investigator (or subinvestigator)'s judgment, contraindicates participation in this clinical trial.