Concomitant administration of hepatotoxic or haematotoxic DMARDs (e.g. methotrexate) is not advisable.
The active metabolite of leflunomide, A771726, has a long half-life, usually 1 to 4 weeks. Serious undesirable effects might occur (e.g. hepatotoxicity, haematotoxicity or allergic reactions, see Side Effects), even if the treatment with leflunomide has been stopped. Therefore, when such toxicity occur or if for any other reason A771726 needs to be cleared rapidly from the body the washout procedure has to be followed. The procedure may be repeated as clinically necessary.
Combinations with other treatments: The use of leflunomide with antimalarials used in rheumatic diseases (e.g. chloroquine and hydroxychloroquine), intramuscular or oral gold, D-penicillamine, azathioprine and other immunosuppressive agents including Tumour Necrosis Factor alpha-inhibitors has not been adequately studied up to now in randomized trials (with the exception of methotrexate). The risk associated with combination therapy, in particular in long term treatment, is unknown. Since such therapy can lead to additive or even synergistic toxicity (e.g. hepato- or haematotoxicity), combination with other DMARD (e.g. methotrexate) is not advisable.
Co-administration of teriflunomide with leflunomide is not recommended, as leflunomide is the parent compound of teriflunomide.
Switching to other treatments: As leflunomide has a long persistence in the body, a switching to another DMARD (e.g. methotrexate) without performing the washout procedure (see Overdosage) may raise the possibility of additive risks even for a long time after the switching (i.e. kinetic interaction organ toxicity).
Similarly, recent treatment with hepatotoxic or haematotoxic medicinal products (e.g. methotrexate) may result in increased side effects; therefore, the imitation of leflunomide treatment has to carefully be considered regarding these benefit/risk aspects and closer monitoring is recommended in the initial phase after switching.
Skin reactions: In case of ulcerative stomatitis, leflunomide administration should be discontinued.
Very rare cases of Stevens Johnson syndrome or toxic epidermal necrolysis have been reported in patients treated with leflunomide. As soon as skin and/or mucosal reactions are observed which raise the suspicion of such severe reactions, Lefno and any other possibly associated treatment must be discontinued, and a leflunomide washout procedure initiated immediately. A complete washout is essential in such cases. In such case re-exposure to leflunomide is contra-indicated.
Infections: It is known that medicinal products with immunosuppressive properties - like leflunomide - may cause patients to be more susceptible to infections including opportunistic infections.
Rare cases of Progressive Multifocal Leukoencephalopathy (PML) have been reported in patients receiving leflunomide among other immunosuppressants.
Before starting treatment, all patients should be evaluated for inactive ("latent") tuberculosis, as per local recommendations. Patients with a history of tuberculosis should be carefully monitored because of the possibility of reactivation of the infection.
Respiratory reactions: Interstitial lung disease has been reported during treatment with leflunomide. The risk of its occurrence is increased in patients with a history of interstitial lung disease. Interstitial lung disease is a potentially fatal disorders, which may occur acutely during therapy. Pulmonary symptoms, such as cough and dyspnoea, may be a reason for discontinuation of the therapy and for further investigation, as appropriate.
Peripheral Neuropathy: Cases of peripheral neuropathy have been reported in patients receiving Lefno. Most patients improved after discontinuation of Lefno. However there was a wide variability in final outcome, i.e. in some patients the neuropathy resolved and some patients had persistent symptoms. Age older than 60 years, concomitant neurotoxic medications, and diabetes may increase the risk for peripheral neuropathy. If a patient taking Lefno develops a peripheral neuropathy, consider discontinuing Lefno therapy and performing the drug elimination procedure.
Blood pressure: Blood pressure must be checked before the start of leflunomide treatment and periodically thereafter.
Effects on the Ability to Drive and Use Machines: During treatment with Lefno there may be slowing of psychomotor reactions and the patients ability to concentrate due to side effects such as dizziness. In such cases, patients should refrain from driving motor transport and work with potentially dangerous machinery.