Study Evaluating LAMICTAL Extended-Release Therapy Added To Current Seizure Treatments In Patients With Primary Generalized Tonic-Clonic Seizures (PGTC) Seizures

Inclusion Criteria:

• Is ≥13 years of age (male or female).

• Has a confident diagnosis of epilepsy with PGTC seizures for more than 24 weeks priorto the Baseline Phase.

• Has electroencephalogram (EEG) evidence of either spike-and-wave discharges consistentwith PGTC, or at least 2 EEGs with no indication of focal abnormalities. The EEG maybe historical or prospective. Investigators may use a historical EEG as long as thereis appropriate documentation.

• Has a documented history of PGTC seizures with or without other generalized seizuretype(s) with no focal onset, and at least 1 PGTC seizure during the eight consecutiveweeks (i.e., 56 consecutive days) prior to starting the 8-week Baseline Phase.

• Has at least 3 PGTC seizures occurring anytime during an 8-week (i.e., 56 days)prospective Baseline Phase.

• NOTE: When a historical baseline is used, the same time period cannot count fordocumentation of inclusion criteria 4 and 5. Additionally, innumerable seizureactivity will not count towards the number of seizures required forrandomization.

• NOTE: With authorization from GSK, a maximum of four weeks (i.e., 28 days) ofhistorical seizure data may replace up to four weeks (i.e., 28 days) of theprospective Baseline Phase for subjects providing reliable documentation of thefollowing:

1. complete daily seizure diary that includes the number of seizuresexperienced each day along with the exact classification of each seizuretype for consecutive days prior to the prospective Baseline Phase

2. stability of prescribed dosages of background antiepileptic drugs (AEDs)

3. compliance with background AEDs.

• All subjects permitted to use historical seizure data must complete a minimum offour weeks (i.e., 28 days) of the prospective Baseline Phase. The historicalBaseline Phase and the prospective Baseline Phase must equal 56 consecutive days.

• Is currently treated with a stable regimen of one or two AED(s) for at least fourweeks prior to starting the Baseline Phase (historical or prospective).

• NOTE: Benzodiazepines used chronically will be considered to be concurrent AEDs.

• NOTE: Subjects with surgically implanted vagal nerve stimulators (VNS) will beallowed to enter the study provided that all of the following conditions are met:

1. VNS has been in place for at least 24 weeks prior to the Baseline Phase.

2. The settings must remain the same for at least 28 days prior to the BaselinePhase.

3. The settings must remain the same during the Baseline, Escalation,Maintenance and Transition Phases.

4. The battery is expected to last for the duration of the study.

5. VNS is counted as a "concurrent AED."

• Is able and willing to maintain an accurate and complete daily written seizure diary,or has a parent/caregiver who is able and willing to maintain an accurate and completedaily written seizure diary for the entire duration of the study.

• Is able to comply with dosing of study drugs, background AEDs and all studyprocedures.

• Has given written informed consent, or has a parent/legally authorized representativewho has given written informed consent, prior to the performance of any studyassessments.

• If female, and of childbearing potential, must be using an acceptable form of birthcontrol, to include one of the following:

1. Complete abstinence from intercourse for two weeks before exposure to the studydrug, throughout the clinical trial, and for a period after the trial to accountfor elimination of the drug (a minimum of 3 weeks).

2. Consistent and correct use of one of the following methods of birth control:

• Male partner who is sterile prior to the female subject's entry into thestudy and is the sole sexual partner for that female subject

• Implants of levonorgestrel

• Injectable progestogen

• Oral contraceptive (either combined, with at least 50mcg estrogen for womenon enzyme-induced AEDs, or progestogen only)

• Any intrauterine device (IUD) with a documented failure rate of less than 1%per year

• Double barrier method consisting of spermicide plus a mechanical barrier (e.g., spermicide plus a male condom or a female diaphragm).

• NOTE: Women who have had a hysterectomy, tubal ligation, or arepost-menopausal are considered to be of non-childbearing potential.

Exclusion Criteria:

• Has a history of partial seizures or interictal expression of partial seizures asevidenced by EEG NOTE: EEG may be historical or prospective.

• Has had status epilepticus within the 24 weeks prior to, or during, the BaselinePhase.

• Is taking three or more background AEDs chronically.

• Has Lennox-Gastaut syndrome.

• Is currently using or has previously used lamotrigine.

• Is currently taking felbamate.

• Is abusing alcohol and/or other substance(s).

• Has taken an investigational drug within the previous 30 days or plans to take aninvestigational drug anytime during the study.

• Is receiving chronic treatment with any medication that could influence seizurecontrol. NOTE: Use of benzodiazepines is allowed.

• Is currently following the ketogenic diet.

• Is planning surgery to control seizures during the study.

• Is suffering from acute or progressive neurological disease, severe psychiatricdisease, or severe mental abnormality that are likely to interfere with the objectivesof the study.

• Has any clinically significant cardiac, renal, hepatic condition, or a condition thataffects the absorption, distribution, metabolism or excretion of drugs.

• Is pregnant, breastfeeding, or planning to become pregnant during the study or withinthe three weeks after the last dose of study drug.