The Pharmaceutical Journal
Vol 269 No 7224 p712
16 November 2002

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Letters to the Editor

Medicines in use

Possibility for folic acid/ methotrexate confusion

From Ms P. Rodriguez and Mr S. G. Athey, MRPharmS

The risk of confusion over the correct dose frequency for oral methotrexate is well known. We write to draw attention to a further problem: the risk of confusion between methotrexate and folic acid.

A patient had been treated with methotrexate 5mg once weekly and folic acid 5mg on the other six days of the week for about 12 months. The patient was competent, well aware of the regimen and not on any other medication. The methotrexate tablets were usually dispensed in a plastic bottle and folic acid supplied in a blister pack. On one occasion folic acid was also dispensed in a plastic bottle. Despite familiarity with the treatment and with the differences in tablet strengths and directions, the patient took one methotrexate 2.5mg tablet daily for six days. The error became apparent when the methotrexate tablets ran out and the patient self-referred to the hospital's accident and emergency department. There were no lasting effects of this overdose but the incident raises questions about risks associated with medicines of similar appearance as well as risks associated with providing medicines in packaging different from the norm.

Both methotrexate 2.5mg and folic acid 5mg tablets are small, round, uncoated yellow tablets and they are frequently prescribed in combination. This incident indicates that even competent patients, familiar with their normal treatment, can ignore labelled directions and confuse medicines of similar appearance. Methotrexate 10mg tablets and 2.5mg tablets are of a similar size and the outcome would have been more serious had the patient been prescribed a higher dose and taken 10mg of methotrexate daily for six days.

Some hospital trusts have discontinued the use of methotrexate 10mg tablets and this potentially reduces the risk of a high overdose. Patients may, however, still receive 10mg tablets when obtaining repeat prescriptions via their general practitioners. Methotrexate tablets might usefully be manufactured with a distinctive shape and size to reduce the risk of confusion. Pharmacists might also inform patients when the packaging of drugs changes in what might be critical circumstances, such as those described above.

Pauline Rodriguez
Dermatology Sister

Steve Athey
Chief Pharmacist
York Health Services Trust

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