Most methotrexate harm in rheumatology clinics is not idiosyncratic. It comes from four failures of counselling, each preventable in the consultation where the drug is started.
First, the frequency. Weekly, not daily, and the patient must be able to say it back. Daily dosing errors cause pancytopenia and mucositis and they kill people, and they happen most often when a second prescriber, a pharmacy label or a hospital drug chart intervenes. Name the day, write it on the box, and tell the patient that any doctor who prescribes it daily has made a mistake. Second, the interactions that matter in practice are not exotic: trimethoprim-sulfamethoxazole, which is prescribed casually for urinary symptoms and is the commonest cause of methotrexate-related pancytopenia, and non-steroidal anti-inflammatories in renal impairment. Third, alcohol and liver monitoring — and the point to make is that a normal transaminase on the day does not license the weekend. Fourth, contraception and conception planning, for men as well as women, with the understanding that this is a conversation to repeat rather than to have once.
Folic acid matters — 5 mg on a different day, or six days a week depending on your local protocol — but it is the easiest part to remember and the least dangerous to get wrong. It is also the one that dominates the consultation because it is comfortable to talk about.
One addition for the patient who becomes unwell: mouth ulcers, sore throat or unexplained fever on methotrexate is a full blood count today, not at the next appointment. Give that instruction in writing, because it is the one that has to survive months of feeling fine.
- Have the patient repeat the day of the week back to you, and write it on the box
- Tell them explicitly that trimethoprim-containing antibiotics must be avoided, and record it in the notes for other prescribers
- Give a written instruction: mouth ulcers, sore throat or fever means a full blood count that day
- Recheck contraception and conception plans at intervals rather than only at initiation, for men too
- Cover folic acid last; it is the part they will remember anyway
Why it matters
Almost all serious methotrexate harm traces back to something that could have been said at the start and usually was not.
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