Our September 9, 2008 Patient Safety Tip of the Week “Less is More….and Do You Really Need that Decimal?” we raised the issue of decimal points leading to excessive doses and whether you really need decimal points at all. When do you really need them? You all know you should never use a “trailing zero”, i.e. a zero following a decimal point, because if the decimal point is not seen there is a risk of a 10-fold (or higher) overdose. But what about other numbers following a decimal point? They are important in certain circumstances (eg. a dose of 0.3 mg or 2.7 mg). However, at higher doses they become much less relevant. For example, let’s say you performed a calculation and the result was a recommended dose of a drug is 72.2 mg. Is there really a difference if the patient gets 72 mg. or 72.2 mg of most drugs? Yet ordering the latter dosage increases the risk that the decimal point may not be seen or not input into a computer or missed in a faxed order and the patient gets a 10x overdose. So we strongly recommend that in writing medication orders one specifically decides whether such fractional doses are important or merely place the patient at increased risk of an error.
A related issue is rounding of medication doses. In many cases it is appropriate to “round” the dose to the closest reasonable amount. For example, it might round to the nearest whole number or the nearest first decimal point. But the tolerance for rounding depends on multiple factors and needs to be individualized to specific drugs. Johnson et al (Johnson 2011) convened a group of pediatric experts to review over 100 medications that comprised >95% of all commonly prescribed pediatric medications. They categorized the drugs as fitting one of three categories:
1) medications for which rounding is judiciously used to retain the intended effect
2) medications that are rounded with attention to potential unintended effects
3) medications that are rarely rounded because of the potential for toxicity
They reviewed the literature on each of the drugs and used a Delphi technique to arrive at consensus for categorization of the drugs and the degree of tolerance for rounding. For instance, in the third category drugs having a narrow therapeutic index (eg. digoxin) are rounded with only a 0-2% tolerance. In the second category, drugs like antibiotics or steroids having dose-dependent unintended consequences might have a tolerance of 5-15% and be rounded down to a dose that can be easily administered. Drugs in the first category have dose-dependent intended effects (eg. furosemide) and can be rounded up or down in increments of 10% or so. They derived a list of over 100 drugs with recommended tolerances for rounding that might be adopted in other pediatric organizations.
Johnson KB, Lee CKK, Spooner SA, et al. Automated Dose-Rounding Recommendations for Pediatric Medications . Pediatrics 2011; 128: 2 e422-e428; published ahead of print July 25, 2011, doi:10.1542/peds.2011-0760