It doesn't pay to play the percentages.

314 P&T® • June 2005 • Vol. 30 No. 6 PROBLEM: The Institute for Safe Medication Practices (ISMP) has received several reports in which patients were given undiluted intravenous (IV) epinephrine 1:1,000 (1 mg/ml) instead of the 1:10,000 (0.1 mg/ml) concentration. In each case, the more diluted epinephrine (1:10,000) was available for use, but the staff inadvertently prescribed or selected the 1:1,000 concentration. One error occurred in an outpatient radiology unit, where the nurse on duty rarely administered medications. The patient reacted to the contrast medium with visible hives and respiratory distress. The physician prescribed 3 ml of the 1:10,000 concentration IV, but 3 ml of the 1:1,000 concentration was administered in error. This mistake resulted from a lack of understanding about the difference between the two concentrations. In this case, however, there was an additional problem: the dilutions were difficult to differentiate, because “1,000” looks like “10,000.” In another case, a physician’s assistant ordered the incorrect concentration for a patient in an urgent-care clinic. The nurse administered the agent without recognizing the problem. In fact, there was no warning anywhere on the ampules of these products about the need to dilute the 1:1,000 concentration before IV administration. Both patients experienced rapid heart rates and an elevated blood pressure, necessitating an overnight hospital stay. These errors highlight an ongoing problem with drug concentrations. Typically, the contents of most injectable medications are given as their mass concentration—in milligrams (mg) or micrograms (mcg) per milliliter (ml). For a few drugs, however, their concentrations are expressed as a dilution ratio or percentage (e.g., epinephrine 1:1,000, lidocaine 1%). These expressions tend to result in errors, as evidenced by studies showing that knowledge about concentrations expressed as a ratio or percentage—even among physicians and emergency medicine residents—is inadequate.1–3 More alarming is the fact that these poorly understood expressions are particularly prevalent with drugs used for resuscitation (e.g., calcium, epinephrine, lidocaine, magnesium sulfate, neostigmine, and sodium bicarbonate). Thus, the occurrence of an inappropriate dose or a life-threatening delay in treatment is quite possible, especially if these drugs are prescribed in milligrams (for which prior knowledge of ratio or percent concentrations and calculations is required) or milliliters (which is a problem if multiple concentrations exist). To cite one example, a newborn stopped breathing, and a Code Blue alert went into effect. An epinephrine dose was ordered in milliliters. Despite much initial confusion, a pharmacist who attended the patient was able to guide the staff in giving the proper dose, because both 1:1,000 and 1:10,000 dilutions were available on the “code cart.” The neonatal nurses and physicians had assumed that only the 1:10,000 dilution was available on the cart.