Inclusion Criteria:

A subject will be eligible for inclusion in this study only if all of the following criteria apply:

1. Male or female subject with a clinical diagnosis of probable Alzheimer's disease in accordance with NINCDS-ADRDA criteria (Appendix 2).

   (Note: National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and Alzheimer's Disease and Related Disorders Association (ADRDA).)

2. Subject has mild to moderate Alzheimer's disease as defined by a MMSE score 10 to 26 inclusive at Screening.
3. Hachinski Ischemia Score ≤ 4 at Screening (See Appendix 3).
4. Age ≥50 and ≤90 years.
5. At least 6 months of ongoing acetylcholinesterase inhibitor therapy for Alzheimer's disease, with stable dosing for at least the last 2 months (and with no intent to change for the duration of the study).
6. Current use of medication is in accordance with the criteria listed in Table 2 (Permitted Medications, Section 8.1).
7. Female subjects must be post-menopausal (i.e. >1 year without menstrual period), surgically sterile, or agree to use adequate method of contraception (Appendix 4) for the duration of the study. Female subjects who are pre-menopausal or who have been post-menopausal for <1 year must undertake pregnancy testing (urine test) at Visit 1, which must be negative.

8. Brain CT or MRI scan performed within the past 12 months or at Screening, showing no evidence of any other potential cause of dementia other than Alzheimer's disease.

   (Note: Questionable CT or MRI scans should be discussed with the medical monitor, using central imaging guidelines.)

9. Neurological exam without focal changes (excluding changes attributable to AD or peripheral trauma).
10. Subject has the ability to comply with procedures for cognitive and other testing.

11. Subject lives with (or has substantial periods of contact with) a regular caregiver who is willing to attend all visits, oversee the subject's compliance with protocol-specified procedures and study medication, and report on subject's status.

    (Note: A non-cohabiting caregiver must spend sufficient time with the subject so that, in the opinion of the Investigator, the caregiver can reliably assess cognitive function, activities and behavior, and report on the subject's compliance and health. As caregiver time spent with a potential subject is anticipated to be highly variable across countries and cultures, GSK will consider a variety of different measures by which this stipulation may be met, and GSK should be consulted if adequacy of a caregiver situation is in doubt. However, as guidance, the ability for a caregiver to meet his/her expected responsibilities for this study would normally be possible when the caregiver spends no less than 10 hours per week with the subject, divided over multiple days.)

12. Subject has provided full written informed consent prior to the performance of any protocol-specified procedure; or if unable to provide informed consent due to cognitive status, full written informed consent on behalf of the subject has been provided by a legally acceptable representative.

    (Note: Consent by legally acceptable representative is allowed where this is in accordance with local laws, regulations and ethics committee policy.)

13. Caregiver has provided full written informed consent on his/her own behalf prior to the performance of any protocol-specified procedure.
14. Subjects considered for enrolment must have a QTc (either QTc B (Bazett's correction) or QTc F (Fridericia's correction)) <450msec at Visit 1, 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]).)

Exclusion Criteria:

A subject will not be eligible for inclusion in this study if any of the following criteria apply:

1. Diagnosis of possible, probable, or definite vascular dementia in accordance with NINDS-AIREN criteria (Appendix 5).

   (Note: National Institute of Neurological Disorders and Stroke (NINDS) and Association Internationale pour la Recherche et l'Enseignement en Neurosciences (AIREN).)

2. History or evidence of any other CNS disorder that could be interpreted as a cause of dementia: e.g. cerebrovascular disease (stroke, hemorrhage), structural abnormality, epilepsy, infectious or inflammatory/demyelinating CNS conditions, Parkinson's disease.

3. Evidence of the following disorders: current vitamin B12 deficiency, positive syphilis serology, or active thyroid dysfunction (particularly that suggestive of hypothyroidism), including abnormally high or low serum levels of thyroid stimulating hormone (TSH), that are clinically significant in the opinion of the investigator.

   (Note: Testing is required for each parameter only when no result is available from previous 12 months.)

4. History of Type 1 diabetes mellitus or secondary diabetes mellitus.
5. Type 2 diabetes mellitus where the subject is being treated with insulin, a PPARγ agonist, or an insulin secretagogue (e.g. a sulfonylurea or glitinide).
6. Any patient with an HbA1c ≥8.5%. (See Section 6.3.8.4 for Safety Measures for Enrolled Subjects with Type 2 Diabetes Mellitus.)
7. History or clinical/investigational evidence of congestive heart failure defined by the New York Heart Association criteria (Class I to IV cardiac status; Appendix 6).
8. History of cardiovascular event within the last 6 months (i.e. intervention, percutaneous coronary intervention, vascular surgery, acute coronary syndrome [non Q-wave myocardial infarction, Q-wave myocardial infarction, unstable angina] or significant arrhythmia; or major intervention (e.g. cardiac surgery or angiography plus stenting) scheduled).

9. History of significant psychiatric illness such as schizophrenia or bipolar affective disorder that in the opinion of the Investigator would interfere with participation in the study, major depressive disorder (according to DSM-IV) in the past year, or current active depression requiring initiation of treatment.

   (Note: If not currently treated, but active depression is suspected, the Cornell Scale for Depression in Dementia (CSDD, Appendix 7) can be used by the Investigator as a guide for deciding whether a prospective subject requires treatment. If the subject has a CSDD score >7, the Investigator should decide if the subject has depression in need of prescribed medication, and a CSDD >12 is considered a strong indicator that treatment is needed. Subjects will be allowed to re-screen after their depression has been adequately managed for >3 months.)

10. History or presence of gastro-intestinal, hepatic, or renal disease or other condition known to interfere with the absorption, distribution, metabolism, or excretion of drugs, or any other clinically relevant abnormality, medical or psychiatric condition, which, in the opinion of the Investigator, makes the subject unsuitable for inclusion in the study.
11. Clinically significant peripheral edema at the time of screening.
12. Current or recent drug or alcohol abuse or dependence (defined by DSM-IV criteria for substance-related disorders), or recent or remote history of the same if that could be a contributing factor to the dementia.
13. Systolic blood pressure >165 or <90 mmHg or diastolic blood pressure >95 or <60 mmHg at the time of screening.
14. Clinically significant anemia (i.e. hemoglobin <11 g/dL for males or <10 g/dL for females) or presence of hemoglobinopathies which would prevent accurate assessment of HbA1c.
15. Abnormal kidney function tests (>1.5 times the upper limit of normal (ULN)).

16. ALT, AST, or alkaline phosphatase values >2.5 times the ULN, total bilirubin values >1.5 times the ULN, or history of severe hepatobiliary disease (e.g. hepatitis B or C, or cirrhosis, Child-Pugh Class B/C).

    (Note: For subjects with a diagnosis of Gilberts Syndrome and an isolated increase in total bilirubin >1.5 ULN, fractionation should be performed. If all of the following conditions are met, the patient may enter or remain in the study, even if total bilirubin >1.5 ULN: •an elevated unconjugated (indirect) bilirubin;

    • the percentage of direct bilirubin <35%;
    • ALT, AST, and alkaline phosphatase <2.5 ULN if subject is in screening (<2.0 ULN for Canadian subjects only), or ≤3 ULN if subject is already randomized into the study)
17. History of a bone marrow transplant.
18. Subject is unable (with assistance, if appropriate) to take study medication as prescribed throughout the study or is at risk of non-compliance with study medication or procedures.
19. Subject is an immediate family member or employee of the participating Investigator, of any of the participating site staff, or of GSK.
20. In France, a subject is neither affiliated with nor a beneficiary of a social security category.
21. The French subject has participated in any study using an investigational drug during the previous 30 days or 5 half-lives (whichever is longer).
22. Cognitive tasks prescribed for cognitive rehabilitation and performed under medical supervision are prohibited for 6 months prior to Screening, as well as for the duration of the study.

This amendment is country-specific and applies only to sites in Canada. The change was not incorporated into the body of the current amendment.

(1) Change in Exclusion criterion #16 regarding ALT cutoff in order to meet regulatory requirements.

This amendment will apply to:

• 5.2.2 Exclusion Criteria (p.31)

  a.Original Verbatim Text:

  1.ALT, AST, or alkaline phosphatase values >2.5 times the ULN, total bilirubin values >1.5 times the ULN, or history of severe hepatobiliary disease (e.g. hepatitis B or C, or cirrhosis, Child-Pugh Class B/C).

  b.Amended Text: 2.ALT, AST, or alkaline phosphatase values >2.0 times the ULN, total bilirubin values >1.5 times the ULN, or history of severe hepatobiliary disease (e.g. hepatitis B or C, or cirrhosis, Child-Pugh Class B/C).