Methotrexate Prescription Written as Daily Therapy
A 58-year-old woman with rheumatoid arthritis presents a new e-prescription: methotrexate 2.5 mg tablets, 3 tablets once daily for a 30-day supply; folic acid 1 mg once daily; and ibuprofen 400 mg as needed. She has no prior methotrexate use. The technician begins filling the prescription while the pharmacist reviews it. The patient says she was told to take three small tablets every day and asks whether to take them with food. She weighs 70 kg, serum creatinine is 0.8 mg/dL, liver function tests are normal, and she is postmenopausal. The e-prescription cannot be edited by the pharmacy, and the prescriber is initially unreachable. If filled as written, 90 tablets would be dispensed.
1. What is the prescription error, and why is it dangerous?
Read the worked answer
Methotrexate for rheumatoid arthritis is dosed weekly, not daily. The prescription would give 7.5 mg × 7 = 52.5 mg per week, about seven times the intended weekly dose of 7.5 mg. Daily dosing can cause severe bone marrow suppression, mucositis, hepatotoxicity, and renal failure. Folic acid is appropriate supportive therapy but does not prevent this error. Ibuprofen may increase methotrexate toxicity, especially if renal function declines. The prescription is not dispensable as written.
2. What immediate actions should the pharmacist take?
Read the worked answer
Do not dispense or let the technician finish the fill. Contact the prescriber to confirm the intended weekly regimen and request a new e-prescription because the current one cannot be edited. Document the intervention and the prescriber's response. If confirmed as 7.5 mg weekly, the quantity for 30 days is 3 tablets per week × 4 weeks = 12 tablets, not 90. If the prescriber cannot be reached, do not dispense; offer to contact the patient's rheumatologist or arrange urgent review. Report the near miss through the incident system and review whether a weekly-dosing alert appears at order entry.
3. Assuming the prescriber confirms weekly dosing, what counselling should be given?
Read the worked answer
Counsel the patient to take three 2.5 mg tablets once weekly on a fixed day, never daily, and not to double a missed dose. Take folic acid as directed, usually on days other than methotrexate. Avoid alcohol, use effective contraception if applicable, and report mouth ulcers, fever, sore throat, bruising, bleeding, shortness of breath, or dark urine. Avoid starting NSAIDs without advice. Explain that blood tests for CBC, liver, and kidney function are needed. Confirm understanding with teach-back and provide a written weekly schedule.