 Each cohort will consist of four subjects who will be randomised to receive GSK2126458 three subjects or placebo one subject for approximately 8 days 7 to 10 days. On Day 1 they will receive their first dose of GSK2126458 or placebo and safety, tolerability and PKPD in the blood will be measured for up to 8 hours post-dose. Subjects will then be discharged from the site with study drug until the last day of dosing. They will also receive hand held spirometers and instructions on action to be taken in case of deterioration in pulmonary function or any other adverse events AEs. On the last day of dosing they will return to the site for a repeat of the Day 1 procedures. 