Which medication errors are prevented by inserting a zero in front of a decimal

Published January 24, 2008

Matthew Grissinger, RPh, FASCP
Medication Safety Analyst
Institute for Safe Medication Practices
Huntingdon Valley, Pennsylvania

Susan Proulx, PharmD
President, Med-E.R.R.S.
Institute for Safe Medication Practices
Huntingdon Valley, Pennsylvania

US Pharm. 2008;33(1):74. Numbers containing decimal points are a major source of error, and when misplaced, can lead to misinterpretation of prescriptions. Decimal points can be easily overlooked, especially on prescriptions that have been faxed, prepared on lined order sheets, or written on carbon and no-carbon-required (NCR) forms (often used in hospitals and long-term care facilities). If a decimal point is missed, an overdose may occur. The importance of proper decimal point placement cannot be overstated.

A decimal point should always be preceded by a whole number and never left "naked." Decimal expressions of numbers less than 1 should be preceded by a zero (0) to en!= hance visibility. For example, without a leading zero, a prescription for "Haldol .5 mg"was misinterpreted and dispensed as "Haldol 5 mg."

In addition, a whole number should never be followed by a decimal point and a zero. These "trailing zeros" (e.g., 3.0) are a frequent cause of 10-fold overdoses and should never be used. For example, when prescriptions have been written for "Coumadin 1.0 mg," patients have received 10 mg in error.

Dangerous use of decimals can also be problematic if they appear in electronic order entry systems or on computer-generated labels. A newly admitted hospital patient told her physician that she took phenobarbital 400 mg PO three times daily. Subsequently, the physician wrote an order for the drug in the dose relayed by the patient. Prior to dispensing, however, a hospital pharmacist investigated the unusually high dose. When he checked the prescription vial, he found that it was labeled as "phenobarbital 32.400MG tablet." The label indicated that 30 tablets were dispensed with instructions to take one tablet three times daily. The hospital pharmacist contacted the outpatient pharmacy and suggested that the computer expression be changed to avoid serious medication errors. The pharmacy management agreed that the trailing zeros appearing on labels might pose a risk, and they made the change immediately.

• Educate staff about the dangers involved with expressing doses using trailing zeros and "naked" decimal points.
• Eliminate dangerous decimal dose expressions from electronic order entry screens, computer-generated labels, and preprinted prescriptions.
• Avoid using decimals whenever a satisfactory alternative exists. For example, use 500 mg in place of 0.5 grams.

• Identify drugs with known 10-fold differences in dosage strength (e.g., levothyroxine 25 mcg and 250 mcg) and place reminders in electronic order entry systems and on pharmacy shelves as reminders to double check the dosage strength.
• Eliminate the lines on the back copy of NCR forms so that the recipient can clearly see decimal points or other marks that were made on the top copy.
• When sending and receiving prescriptions via fax, health care practitioners should keep in mind that decimal points can be easily missed or inadvertently added due to "fax noise." Whenever possible, prescribers should give the original prescription to the patient to take to the pharmacy for verification. Pharmacists should carefully review faxed prescriptions and clarify prescriptions that contain "fax noise."

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