This 2 arm study will investigate the pharmacokinetics of simvastatin and methotrexate in combination with tocilizumab to assess any potential drug interactions. Patients will be randomized to receive either tocilizumab (10mg/kg iv infusion on day 8) + methotrexate (10-25mg po /week) or tocilizumab + methotrexate + simvastatin (40mg po on days 1, 15 and 43). Blood samples will be taken for analysis at intervals up to day 44. The anticipated time on study treatment is <3 months, and the target sample size is <100 individuals.