practice partner
Express levothyroxine
doses in micrograms
not milligrams
P
hysicians are being urged to
express doses of levothyroxine in
micrograms not milligrams after
the Institute for Safe Medication
Practices (ISMP) Canada became aware of
errors involving the medication.
“Multiple cases of errors and near misses
involving the levothyroxine dose conversions
from milligrams (mg) to micrograms (mcg)
and vice versa have been reported to ISMP
Canada and in the literature,” stated a recent
ISMP bulletin (Volume 17, Issue 3)
The Canadian manufacturer of levothyrox-
ine labels express levothyroxine doses in mi-
crograms (mcg) only. However, throughout
the medication-use process (e.g., prescribing,
dispensing, and administration), the thyroid
medication doses may be expressed in micro-
grams (mcg) or in milligrams (mg).
As a result, patients and health-care
providers may need to convert doses from
milligrams (mg) to micrograms (mcg), or
vice versa, to match the prescribed dose to
46
Dialogue Issue 2, 2017
a particular product, leading to errors in
calculations.
A common calculation error occurs when
converting between 0.025 mg and 25 mcg,
causing a 10-fold error in dosing. The resul-
tant dose, sometimes 250 mcg rather than
25 mcg, is considered a reasonable dose for
some patients and, as such, does not raise a
red flag for most practitioners.
ISMP Canada strongly recommends that
levothyroxine doses be expressed consis-
tently in micrograms (mcg), not milligrams
(mg), in all written or computer-generated
prescriptions and health records, pharmacy
systems, medication administration records,
provincial/territorial drug databases, drug
information systems, and patient materials.
Using microgram units reduces the need
for decimals (which can lead to errors), al-
lows the dose to correspond directly to the
manufacturer’s label (avoiding the need for
conversion), and will standardize how levo-
thyroxine information is communicated.
MD
Process of converting doses between
different units of measurement blamed
for errors