Ironing out a problem: Measuring pediatric
iron products safely
From the May 5, 1999 issue
PROBLEM:: In previous issues, ISMP has advised prescribers
to avoid ordering medications by volume, such as milliliters,
teaspoons or amps. Similarly, medication doses are sometimes
dangerously ordered by the "dropperful." Such an order, "ferrous
sulfate 1 dropperful 3 times daily," was recently written
for a pediatric patient who weighed 8 kg. There are several
problems with this order. First, there is too much room for
misinterpretation of what might constitute a dropperful. One
individual might consider it to be a dropper filled to the
upper calibration mark, which was the intention in this case.
Others might consider it to be, literally, a full dropper,
and yet others may consider it acceptable to use a household
dropper or a dropper supplied for another product. Likewise,
another problem is variation in the measurement scales on
droppers supplied with different products. One common ferrous
sulfate product, FER-IN-SOL by Mead Johnson, contains 15 mg
of elemental iron per 0.6 mL. It comes with a dropper that
has two 0.3 mL gradations (0.3 mL and 0.6 mL). However, droppers
included with some generic equivalent products have a different
scale with significant room for overfill. In fact, the total
volume of one generic product's dropper, when literally "filled,"
is 1.8 mL.
Proper dosing of iron in children is critical if iron toxicity
is to be avoided. For example, to treat iron deficiency, the
usual dose for children 6 months to 2 years, is up to 6 mg/kg/day
in 3 to 4 divided doses. In this case, the appropriate dose
for the 8 kg child would have been about 48 mg of elemental
iron daily, an amount approximated by measuring 0.6 mL (15
mg of elemental iron) on the Fer-In-Sol dropper, and giving
it three times daily. However, in this case, the hospital
stocked ferrous sulfate drops by the generic manufacturer.
With 15 mg of elemental iron per 0.6 mL in the product, if
each "dropperful" is measured to the top of the 1 mL scale
and given tid, the child would receive a 75 mg total daily
dose or about a 50% overdose. Filled to capacity (1.8 mL),
a dropperful given tid would deliver a total daily dose of
135 mg, which is close to 20 mg/kg, the amount considered
minimally toxic for a child of this weight.
SAFE PRACTICE RECOMMENDATION:The pharmacist who screened
the order was confused by the dosing instructions and acted
in proper fashion by calling the prescriber for clarification.
The ordered dose of elemental iron was changed from "one dropperful"
to "15 mg (0.6 mL) three times a day." To avoid confusion,
the proper way to prescribe the dose of any medication is
by weight, such as mg. However, many liquid products have
varying dose measurement devices (droppers, dosing cups, etc.)
which may be calibrated only by volume or may indicate a volume
that correlates with another product's dose in milligrams.
Therefore, it is critical that dosing directions on prescriptions
and MARs be expressed as both mg weight and volume (as was
done here after the order was clarified.). Also, only the
measuring device included in the original packaging of a liquid
medication should be used. The Fer-In-Sol package is safer
than generics because it has instructions on proper dropper
use, including correct filling and expelling of liquid, which
is lacking with the generic product. Manufacturers of iron
products should match delivery systems as closely as possible.