Interactions studies have only been performed in adults.
Increased side effects may occur in case of recent or concomitant use of hepatotoxic or haematotoxic drugs or when leflunomide treatment is followed by such drugs without a washout period. Therefore, closer monitoring of liver enzymes and haematological parameters is recommended in the initial phase after switching.
Methotrexate: In patients with rheumatoid arthritis, no pharmacokinetic interaction between the leflunomide (10 to 20 mg per day) and methotrexate (10 to 25 mg per week) was demonstrated.
Vaccinations: No clinical data are available on the efficacy and safety of vaccinations under leflunomide treatment. Vaccination with live attenuated vaccines is, however, not recommended.
Warfarin and other coumarine anticoagulants: There have been case reports of increased prothrombin time, when leflunomide and warfarin were co-administered. Therefore when warfarin or another coumarin anticoagulant is co-administered, close international normalised ratio (INR) follow-up and monitoring is recommended.
NSAIDS/Corticosteroids: If the patient is already receiving nonsteroidal anti-inflammatory drugs (NSAIDs) and/or corticosteroids these may be continued after starting leflunomide.