Eliminating Ratio Expressions on Single Entity Drug Products

Ronald S. Litman, DO; Michael R. Cohen, RPh, MS

Letter to the Editor:

To the Editor:

We would like to update the Anesthesiology community on recent changes in the way that ratio expressions will be labeled on medications with single entity drug labels. The latest update of the United States Pharmacopeia (USP) and The National Formulary (NF) (USP39-NF34), will become official on May 1, 2016, and will no longer allow the use of ratio expressions on single entity drug products (U.S. Pharmacopeia. Labeling <7>, Ratio Expression of Strength. USP 38­NF 33, 2015). The most important drug affected in the field of anesthesiology will be epinephrine, which up until now has been supplied as either a 1-mL ampule of a 1:1,000 solution (usually used subcutaneously for acute bronchospasm) or as a 10-mL vial of a 1:10,000 solution (usually used intravenously as a cardiotonic agent). The 1:1,000 solution will only be displayed as 1 mg/mL, and the 1:10,000 solution will be displayed as 0.1 mg/mL. Other medications affected include isoproterenol (a 1:5,000 injection will be expressed as 0.2 mg/mL), and neostigmine (a 1:1,000 injection will be expressed as 1 mg/mL). The May 1, 2016, date will allow manufacturers and drug information systems time to make these changes. The Institute for Safe Medication Practices (ISMP) had previously petitioned USP to make this change because of an ongoing stream of serious errors where different ratio expressions were confused with one another (www.ismp.org/sc?id=1641). An important exception will be the description of the epinephrine contained within local anesthetic solutions, for example, as lidocaine 1% with epinephrine 1:100,000 injection, or bupivacaine 0.25% with epinephrine 1:200,000 injection. These local anesthetic solutions will retain ratio expressions for the epinephrine component because a decimal notation for such a low strength could easily be misread.

All anesthesiology providers should be aware of the upcoming changes, and should use the new dosing nomenclature when referring to these medications after the changes have been introduced. Once the labels change and they no longer contain the ratio expressions, drug storage labels and orders for these drugs must be communicated using doses expressed in metric weights to avoid confusion. For example, if a prescriber leading a code team calls out for “1:10,000 epinephrine” and the product label no longer contains this ratio expression, practitioners could become confused and administer the wrong strength. In clinical situations that require epinephrine, it will need to be ordered as an absolute mcg or mg dosage and the route specified.


Ronald S. Litman, DO, Medical Director

Michael R. Cohen, RPh, MS, President Institute for Safe Medication Practices Horsham, PA