The primary objective of this study is to evaluate the efficacy and safety of adding GSK2190915 300mg or placebo tablets administered once daily to fluticasone propionate/salmeterol 250/50mcg inhalation powder administered twice daily in uncontrolled asthmatic subjects > or = 18 years of age over the course of 6 weeks treatment.

The secondary objectives are to undertake an exploratory analysis of the efficacy and safety of adding montelukast 10mg administered once daily to fluticasone propionate/salmeterol 250/50mcg inhalation powder administered twice daily and to investigate the pharmacokinetics and pharmacodynamics of GSK2190915 in uncontrolled asthmatic subjects > or = 18 years of age over the course of 6 weeks treatment.

Inclusion Criteria:

• Age: 18 years of age or older
• Non-, former or current smokers with a documented smoking history of ≤ 10 pack years
• Asthma diagnosis as defined by the National Institutes of Health
• Best FEV1 of 50% to <80% of the predicted normal value
• For current and former smokers, a post-albuterol FEV1/FVC ratio of >0.70 at Visit 1/1a (between 5:00AM and 12:00 noon)
• ≥ 12% and ≥200mL reversibility of FEV1
• Must have been using FP/SAL 250/50mcg inhalation powder BID for at least 2 weeks just prior to Visit 1.
• Must be able to replace their current short-acting beta2-agonists with albuterol inhalation aerosol
• Must be able and willing to give written informed consent to take part in the study.
• Must be able and willing to comply with all aspects of the study including completion of daily e-Diary.

Exclusion criteria:

• History of life-threatening asthma
• Recent asthma exacerbation
• Concurrent respiratory disease
• Recent respiratory infection
• Liver disease
• Other concurrent diseases/abnormalities
• Oral candidiasis
• Drug allergy
• Milk protein allergy
• Immunosuppressive Medications
• Administration of systemic, oral or depot corticosteroids within 12 weeks of Visit 1
• OATP1B1 substrates within 4 weeks of Visit 1
• Cytochrome P450 3A4 (CYP 3A4) Inhibitors
• Cytochrome P450 3A4 (CYP 3A4) Inducers
• Investigational Medications
• Compliance: any infirmity, disability, or geographical location which seems likely (in the opinion of the Investigator) to impair compliance with any aspect of this study protocol
• Affiliation with Investigator's Site

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.