This study will investigate the effect of Tafenoquine (TQ) 150 mg tablet ageing (dissolution profiles) on human exposure of TQ comparing the relative bioavailability of TQ from tablets exhibiting different dissolution profiles in healthy subjects. This is a single-centre, 2-arm, randomized open-label, parallel-group study in healthy subjects. All subjects will arrive in the unit approximately 24 hours prior to dosing and will be discharged after the 72-hour post-dose assessments are completed. Subjects will return for outpatient visits on Days 7, 14, 21, 28, and 56 after dosing. A total of 14 subjects (n=7 subjects in each arm) are planned to be enrolled. All subjects will receive a single dose of study medication (2x150 mg TQ tablets + 30 mg TQ SIL in solution) and participate through a 56-day post dose follow-up visit. To enable the application of peripheral microsampling in planned paediatric studies, a comparison of the measured pharmacokinetic (PK) exposure via peripheral blood collection (via microsampling) to venous collection will also be performed in this study.

Inclusion Criteria:

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

• Between 18 and 55 years of age inclusive, at the time of signing the informed consent
• Healthy as determined by the investigator or medically qualified designee based on a medical evaluation including medical history, physical examination, laboratory tests and cardiac monitoring.
• A subject with a clinical abnormality or laboratory parameter(s) which is/are not specifically listed in the inclusion or exclusion criteria, outside the reference range for the population being studied may be included only if the investigator and the GlaxoSmithKline (GSK) Medical Monitor agree and document that the finding is unlikely to introduce additional risk factors and will not interfere with the study procedures.
• Subject values outside the normal range should always be excluded from enrolment.
• Body weight between >=35 kilogram (kg) and <=100 kg.
• Male subjects only.
• Capable of giving signed informed consent as described in study protocol, which includes compliance with the requirements and restrictions listed in the consent form and in the study protocol

Exclusion Criteria:

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

• Alanine Aminotransferase (ALT) and bilirubin >1.5x upper limit of normal (ULN) (isolated bilirubin >1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin <35%).
• Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones).
• QT interval corrected for heart rate according to Fridericia's formula (QTcF) > 450 millisecond (msec) Note: The QTc is the QTcF). Other calculation methods (e.g. QT interval corrected using Bazett's formula [QTcB], QTcF) machine-read or manually over-read are not acceptable.
• Use of prescription (except acetaminophen at doses of 2 grams/day) or non-prescription drugs, including vitamins, herbal and dietary supplements (including St John's Wort) within 7 days (or 14 days if the drug is a potential enzyme inducer) or 5 half-lives (whichever is longer) prior to the first dose of study medication, unless in the opinion of the Investigator and GSK Medical Monitor the medication will not interfere with the study procedures or compromise subject safety.
• History of regular alcohol consumption within 30 days of the study defined as: an average weekly intake of >14 drinks for males. One drink is equivalent to 12 grams (g) of alcohol: 12 ounces (360 millilitre [mL]) of beer, 5 ounces (150 mL) of wine or 1.5 ounces (45 mL) of 80 proof distilled spirits.
• Positive results for drugs of abuse as mentioned in protocol.
• Cotinine levels indicative of smoking or history or regular use of tobacco- or nicotine-containing products within 30 days prior to screening.
• History of sensitivity to TQ, or components thereof or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicates their participation.
• History of thalassaemia; or current or past history of methemoglobinemia or methemoglobin percentage above the reference range at screening.
• Presence of hepatitis B surface antigen (HBsAg), positive hepatitis C antibody test result at screening or within 3 months prior to first dose of study treatment.
• A positive pre-study drug/alcohol screen.
• A positive test for human immunodeficiency virus (HIV) antibody.
• The subject has been dosed with TQ within 10 months prior to being dosed in this study.
• Where participation in the study would result in donation of blood or blood products in excess of 500 mL within a 15 days of dosing with TQ or matched-placebo.
• The subject has participated in a clinical trial and has received an investigational product within the following time period prior to the first dosing day in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer).
• Exposure to more than four new chemical entities within 12 months prior to the first dosing day.
• Subjects with a hemoglobin values outside the lower limit of normal range. A single repeat is allowed for eligibility determination.
• Documented phenotypic Glucose-6-phosphate dehydrogenase (G6PD) deficiency, determined by a quantitative assay of enzyme activity. Defined as <70% of locally defined median.