From Mr J. P. Mason, MRPharmS
SIR,-I would like to bring to the attention of your readers details of a potentially hazardous drug interaction.
A patient of mine who has been taking warfarin for some time was recently started on leflunomide for her rheumatoid arthritis.
I had read a short article on the internet highlighting a potential interaction between warfarin and leflunomide. Consequently, I advised my patient to have her INR (international normalised ratio) checked before starting to take leflunomide and again once she had been taking leflunomide for a few days.
Fortunately, she followed my advice since, after only three doses of leflunomide 100mg, her INR had increased from 2.5 to greater than 6. She was referred to hospital for observation and treatment.
This case reinforces the old adage that pharmacists should be extra vigilant whenever a patient taking warfarin has his or her concomitant medication altered.
Jonathan Mason
Faversham, Kent