United States of America. Thorough understanding of proper directions is especially important when the patient receives a prescription for alternating doses of warfarin (Coumadin). The ISMP has received two reports recently of patients’ misunderstanding that resulted in hospitalization.

In the first case, the patient was given a prescription for Coumadin 2.5 mg, with directions to take “2.5 Mon, Tue, Thu, Fri, Sat and 5 Wed and Sun”. The patient misunderstood these directions and took 2.5 tablets or 5 tablets instead of 2.5 mg or 5 mg. After two weeks, the patient developed gastrointestinal bleeding and had an INR greater than 60. With 2.5 mg tablets in the bottle it would have been clearer to direct the patient to take one or two tablets on the desired days.

In another case, a doctor verbally modified prior prescription instructions and told the patient to Atake Coumadin 5 mg on Monday, Wednesday and Friday, alternating with 2.5 mg on remaining days@. No written directions were provided. The patient heard “2.5 tablets” of Coumadin 5 mg in stead of 2.5 mg. She suffered gross haematuria, and was hospitalized with an INR of 26.

Because of the propensity of warfarin to cause injury if misused, it is especially important to verify that patients can demonstrate clear understanding of directions, adverse effects, drug interactions, etc. Patients must receive instructions that follow accepted standards for communicating the dosing schedule.

Reference: ISMP Medication Safety Alert! Vol. 3, Issue 24, 1 December 1998.