Errors in the Use of Medication Dosage Equations

BACKGROUND: Calculation errors in prescribing are a well-recognized problem; however, no systematic studies of actual errors involving calculation or other errors in the use of drug dosage equations are available. OBJECTIVE: To characterize the nature and potential adverse consequences of actual prescribing errors involving dosage equations. DESIGN: Analysis of the characteristics of 200 consecutive prescribing errors with potentially adverse outcomes involving dosage equations. SETTING: Tertiary care teaching hospital. MEASUREMENTS: Potential adverse outcomes, prescribing service, medication class, and the process point at which the error was made. RESULTS: Errors most commonly involved children (69.5%) and antibiotics (53.5%). Forty-two percent of errors were considered to put the patient at risk for a serious or severe preventable adverse outcome. Errors in decimal point placement, mathematical calculation, or expression of dosage regimen accounted for 59.5% of dosage errors. The dosage equation was wrong in 29.5% of dosage errors. CONCLUSIONS: The use of equations to determine medication dosages presents considerable risk to patients for errant dosing and subsequent adverse events or therapeutic failure. Errors may occur in any component of a dosage equation. Health care organizations should implement procedures to reduce the risk for errors resulting from the use of dosage equations.