Oral Contraceptive Interaction Study for GW273225

GW273225 is in development for epilepsy and bipolar disorder and can affect women of child bearing potential. A clear understanding of the potential interaction between oral contraceptives and GW273225 is therefore important for clinical investigation of GW273225 in a large number of patients. This study will investigate whether there is any effect of GW273225 upon the components of combined oral contraceptive, and also whether taking oral contraceptives affects the pharmacokinetics (PK) of GW273225. 26 healthy female subjects, aged 18-45 years will take an oral contraceptive (150ug levonorgestrel and 30ug ethinylestrdiol; The study will include a screening period, two cycles on oral contraceptive with GW273225 at 25 mg once per day administered from the start of the second COC cycle for 47 days. There will be a follow-up visit 14-21 days later.