Medication errors in the outpatient setting: classification and root cause analysis.

OBJECTIVES To understand and classify causal factors linked to medication errors and to define opportunities for systematic changes to improve the safety of prescription medication use. DESIGN, SETTING, AND PARTICIPANTS All recipients of liver, kidney, and/or pancreas allografts followed up by an academic medical center and encountered in the acute care facility, outpatient clinic, or by telephone during 12 months (April 1, 2004, through March 31, 2005). Errors were sought by specific review of the expected and actual medication lists. Main Outcome Measure Proportion of medication errors in each of 5 classifications developed through iterative revision. Definitions included failure to provide a correct prescription (prescription error); deliver a prescribed medication to the patient (delivery error); possess enough medication for a 24-hour or greater supply (availability error); accurately use an available, prescribed medication (patient error); and identify the type, dosage, or frequency of a medication (reporting error). RESULTS We identified 149 errors in 93 patients who were prescribed a mean of 10.9 medications each. Adverse events were associated with 48 errors (32%), including hospitalization (17 patients) or outpatient invasive procedure (3 patients) in 13%. Nine episodes of rejection and 6 failed allografts were identified. The most common error type was patient error in 83 errors (56%) with prescription errors in 20 errors (13%), delivery errors in 20 errors (13%), availability errors in 15 errors (10%), and reporting errors in 12 errors (8%). Root cause analysis identified the patient as the cause in 101 errors (68%) while pharmacies and other sectors of the health care team caused 41 errors (27%). Finances were linked to 7 errors (5%). Error frequency was estimated during 4 weeks of outpatient visits at 15 of 219 visits. CONCLUSIONS Outpatient medication errors are abundant, often occult, and associated with significant adverse events in a complex transplant population. The health care system is associated with nearly one third of errors.