Accidental over-anticoagulation: substitution error by a foreign pharmacy.

OBJECTIVE: To describe an episode of inadvertent and excessive anticoagulation caused by mistaken substitution of medication by a pharmacy outside the US. CASE SUMMARY: A 57-year-old white woman was found to have profound prolongation of her prothrombin time (56.9 sec) and international normalized ratio (22.18), with other coagulation parameters relatively normal. She had no prior history of bleeding diatheses and was not taking any prescribed anticoagulants. Her coagulopathy rapidly corrected with the administration of fresh frozen plasma and vitamin K. After her medications were visually inspected, it was discovered that she had purchased her prescription medications from a pharmacy in Mexico and that she inadvertently had been taking a preparation of warfarin (proprietary name in Mexico, "Romesa") instead of the prescribed ramipril for her hypertension (proprietary name in Mexico, "Ramace"). After removal of the incorrect medication, she experienced no further prolongation of her coagulation parameters. DISCUSSION: Medication errors contribute significantly to adverse events for patients. The frequency of different types of medication errors is reviewed, and problems specific to the use of warfarin are detailed. Circumstances that might lead to a patient seeking prescription medication outside of the US are also discussed. CONCLUSIONS: The acquisition of prescription medications from pharmacies outside of the US can have adverse consequences, especially if the foreign name of the medication is different from its American name, while sounding similar to other medications that also might be dispensed in foreign pharmacies.