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It doesn't pay to play the percentages
From the October 16, 2002 issue
PROBLEM: Several incidents have been reported where undiluted
epinephrine 1:1,000 (1 mg/mL) was given IV to patients instead
of using the 1:10,000 (0.1 mg/mL) concentration. In each case,
the more diluted epinephrine (1:10,000) was available for use,
but 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 developed
a reaction to contrast media, 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. Lack of understanding the difference between the two
concentrations led to the error, but an additional problem is
that the dilutions are hard to differentiate since 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, and the nurse administered it without recognizing the
problem. In fact, a warning to dilute the 1:1,000 concentration
before IV administration is not mentioned anywhere on the ampuls
of these products. Both patients developed rapid heart rates
and increased blood pressures, necessitating an overnight stay
in the hospital.
These errors highlight an ongoing problem of drug concentration
presentation. Typically, the contents of most injectable medications
are given as their mass concentration (mg or mcg per mL).
But a few drugs have concentrations expressed as a dilution
ratio or percentage (e.g., epinephrine 1:1,000, lidocaine
1%). These expressions are error-prone, especially in light
of studies that have shown that knowledge about concentrations
expressed as a ratio or percentage is inadequate, even among
physicians and emergency medicine residents.1-3
Most alarming, these poorly understood expressions are particularly
prevalent with drugs used for resuscitation (e.g., calcium,
epinephrine, lidocaine, magnesium sulfate, neostigmine, sodium
bicarbonate). Thus, an inappropriate dose or life-threatening
delay in treatment is quite possible, especially if these
drugs are prescribed in mg (which requires prior knowledge
of ratio or percent concentrations and calculations) or mL
(which is a problem if multiple concentrations exist). To
cite one example, at a neonatal code recently, an epinephrine
dose was ordered in mL. Despite a good deal of confusion at
first, a pharmacist who attended the code was able to guide
staff regarding the proper dose for the patient since both
1:1,000 and 1:10,000 dilutions were available on the code
cart. Neonatal nurses and physicians had assumed that only
the 1:10,000 dilution was available on the code cart.
SAFE PRACTICE RECOMMENDATION: Based on research findings
and everyday practice experiences, do not expect all health
care practitioners to be familiar with percent or ratio expressions
of concentrations, or to be adept at calculating doses for
drugs with concentrations expressed in this manner. Therefore,
it would be helpful to create a dose conversion chart reflecting
concentrations that are available in your facility and post
them on code carts and in other areas where emergency medications
may be prepared. Since an independent double check by another
clinician may not be feasible in emergency situations, encourage
staff to refer to the dose chart before administration of
these products.
During annual CPR certification for clinical staff, be sure
to review the dose chart and mention potential confusion with
emergency drugs dosed in ratio or percent concentrations.
Also, point out the hazards of ordering injectable medications
by volume alone. Store a single concentration wherever possible
and affix warning labels as appropriate to minimize confusion
between the two concentrations of epinephrine. In some locations,
such as a code cart, it might be feasible to store epinephrine
in 1:10,000 pre-filled 10 mL syringes as the only choice.
In units where multiple concentrations may be needed (such
as the ER), consider applying auxiliary warning labels to
the 1:1,000 ampuls to alert staff to the concentration in
mg and to dilute it before IV use.
Since many of the emergency medications with concentrations
expressed in ratios or percentages date back to before the
1938 Food Drug and Cosmetic Act, they do not fall under current
FDA labeling standards. However, since the issue is so serious,
we have asked FDA to address the problem. While a ratio or
percent expression of concentration may be less dangerous
for topical use products or in local anesthetics, they do
not serve us well when dosing is systemic.
References: (1). Rolfe S, Harper NJ. Ability of hospital
doctors to calculate drug doses. BMJ 1995; 310:1173-4. (2).
Jones SJ, Cohen AM. Confusing drug concentrations. Anaesthesia
2001;56:195-6. (3). Nelson LS, Gordon PE, Simmons MD, et al.
The benefit of houseofficer education on proper medication
dose calculation and ordering. Academic Emergency Medicine
2000; 1311-16.
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