Patients prescribed a highly effective but toxic drug for rheumatoid arthritis and the skin complaint psoriasis are being given safety advice after research suggested that it has been responsible for at least 25 deaths and 26 cases of serious harm in 10 years.
Doctors and pharmacists are being reminded of the hazards of methotrexate, which is one of only six drugs, out of the 13,000 licensed medicines, which are taken weekly.
The National Patient Safety Agency, which issued the alert yesterday, fears that it has sometimes been taken daily, and that there has been confusion about different tablet strengths, lack of clarity in the packaging, mistakes in prescribing, and variation in treatment reviews.
The manufacturers have altered the shape of one tablet because of the confusion about the dosage, and are discussing the packaging with government watchdogs.
The NPSA said the drug, used by about 50,000 people a year outside hospitals, was "a good drug with a good safety profile" when taken at the right frequency, in the right dose, with appropriate checks.
The drug is available in two strengths, 2.5mg and 10mg. Patients typically start on 7.5mg but some need 40mg. Both tablets are yellow and both were round, but the 10mg tablet has been changed to an elongated torpedo.
There has been concern that doctors have not given patients enough information, nor monitored the drug's use sufficiently. Patients are to be given monitoring diaries and IT systems for prescribing and dispensing the drug are to incorporate warnings.
The NPSA, set up three years ago, made methotrexate one of its first priorities for investigation. The government is determined to reduce the number of drug errors made by the NHS but much of the attention has been devoted to cutting errors in hospitals.
Wendy Harris, a senior pharmacist with the NPSA, said: "We have had to tackle this complex problem at a number of levels and have combined forces with industry, and involved patients, clinicians and pharmacists, who have given invaluable feedback about making treatment safer."
The drug, which is also used in hospitals to treat patients with cancer and blood disorders, can affect the blood, kidneys, liver and lungs if taken in too high a dose.
Mrs Harris said: "Methotrexate would not be the only tablets patients are taking at the time.
"It is important they have enough information to use each medicine safely, in the right does, at the right time."
Much of the drive to investigate methotrexate came from Amanda Cale, whose father died aged 71 three years ago after complications, although he was not one of the 25 deaths found in medical literature or reported by professionals.
The family wondered if his life could have been saved by trying an alternative drug, by clear warning being given that breathlessness is a sign of methotrexate poisoning, or by the hospital where he was taken having recognised and treated his symptoms sooner.
Mrs Cale said: "People say: 'Why haven't you sued?' Suing is not going to bring him back. We want to stop it happening to anyone else.
"That is what the agency is about - learning from errors."
