Leflunomide was launched in the USA in 1998 and in Singapore two years later. Leflunomide belongs to the class of disease-modifying anti-rheumatic drugs (DMARDs) and possesses immunomodulating/
immunosuppressive characteristics. It acts as an antiproliferative agent and displays anti-inflammatory properties. Due to its mode of actions, leflunomide is known to increase risks of hepatotoxic and haematoxic adverse effects. Hence close monitoring of patient's blood indices and liver enzymes levels is required.

In an estimate of 400,000 patients exposed to the drug since its launch, 80 have developed interstitial pneumonia. No deaths have been reported until the recent cases in Japan.

On 28 Jan 2004, Japan reported 16 cases of interstitial pneumonia (including 5 deaths) linked to the use of leflunomide over a month period after the product was introduced in Japan in Sep 2003. Nine of the 16 patients were already suffering from lung disease when leflunomide was prescribed to them.

The local package insert of Arava® will be updated to include warning statements that interstitial lung disease has been reported rarely during treatment with leflunomide.