Inclusion Criteria:

• Healthy female subjects aged between 18 and 45 years, inclusive.
• Body weight >50 kg and Body Mass Index (BMI) within the range 19-29.9 kg/m2 inclusive.
• Female subjects of child bearing potential will be eligible to participate if they are established on a Microgynon 30 or Ovranette for the previous month
• If taking a similar ethinyl oestradiol dose (30 or 35 mcg) combined with a progestogen at fixed dose for 21 days then willing to switch to Microgynon 30
• Subjects will use additional contraception as described in the protocol. One of the methods listed in the protocol is acceptable in conjunction with COC as the method of contraception if there is indisputable data that it is >99% effective, otherwise it should be used with a barrier method (condom or occlusive cap (diaphragm or cervical/vault caps) used with spermicidal foam/gel/film/cream/suppository).
• Subjects must smoke ≤ 10 cigarettes per day.
• No abnormality on relevant clinical examination. A subject with a clinical abnormality may be included only if the Investigator in consultation with the GSK Medical Monitor considers that the abnormality will not introduce additional risk factors and will not interfere with the study procedures.
• No abnormality on relevant clinical chemistry or haematology examination at the pre-study medical examination. Subjects with laboratory parameters outside the reference range for this age group will only be included if the Investigator in consultation with the GSK Medical Monitor considers that such findings will not introduce additional risk factors.
• A 12-lead ECG and vital signs at the pre-study medical examination, which are normal. (including QTc which is <450msec)
• The subject has signed and dated written informed consent prior to admission to the study
• The subject is able to understand and comply with protocol requirements, instructions and protocol-stated restrictions.

Exclusion Criteria:

• History or evidence of drug or alcohol abuse within six months of study start.
• Weekly alcohol intake of more than 14 units or an average daily intake of greater than 2 units.
• Female subject pregnant (positive serum human chorionic gonadotrophin (hCG) test at screening) or lactating. HIV, Chronic hepatitis B and C, as evidenced by positive Hepatitis B surface antigen (HBsAg) or Hepatitis C antibody
• Subject has received prescribed or non-prescribed medication (including vitamins and herbal remedies) within 14 days prior to day 1 which in the opinion of the investigator, could have interfered with the study procedures or compromised safety.
• History of gastro-intestinal, hepatic or renal disease or other condition known to interfere with the absorption, distribution, metabolism or excretion of drugs.
• History of thrombotic events or presence of significant risk factors for thrombosis.
• Supine Blood Pressure greater than or equal to 140/90.
• Progestogen- releasing IUD contraceptive.
• Participation in a trial with any drug within 84 days before the start of the study.
• Donation of more than 1500 mL blood in the previous 12 months.
• History or presence of any condition contra-indicated to combined oral contraceptive.
• Any subject where the potential side effects of GW273225 could affect their professional occupation, e.g. operating machinery, driving.
• Any subjects who cannot refrain from driving for the duration of administration of GW273225 and for 3 days afterwards.
• History of clinically relevant skin rashes that, in the opinion of the investigator, might interfere with the conduct of the study.
• Subject has current or past history of seizure disorder or brain injury (traumatic or disease-related), or any condition which, in the opinion of the investigator, predisposes to seizure; subject treated with other medications or treatment regimens that lower seizure threshold; subject undergoing abrupt discontinuation of alcohol or sedatives (including benzodiazepines).