Patient misunderstanding of dosing instructions

OBJECTIVE: To compare outpatients' understanding of medication dosing instructions written in terms of daily frequency with patients' understanding of instructions specifying hourly intervals. DESIGN: Prospective cohort study involving patient interviews. SETTING: A university hospital outpatient pharmacy. PATIENTS: Five hundred patients presenting new and refill prescriptions to the hospital outpatient pharmacy. INTERVENTION: Patients were interviewed using a standardized questionnaire. MEASUREMENTS AND MAIN RESULTS: Of the 71 patients with prescriptions specifying dosing instructions in hourly intervals (e.g., q6h), 55 (77%) misinterpreted the recommended frequency of dosage compared with only 4 (0.93%) of the 429 patients with dosing instructions specifying daily frequency (e.g., qid) (relative risk 83; 95% confidence interval 31-200). This difference remained when patient subgroups were evaluated by education level, new versus refill prescriptions, and analgesic versus nonanalgesic medications. CONCLUSIONS: This study indicates that the intended dosing regimen is frequently misunderstood when the physician writes outpatient prescriptions in hourly intervals. To promote optimal patient compliance, the outpatient prescription label should state the number of times a day a medication is to be taken.