ISMP Safe Medicine September/October 2008, Volume 6, Number 5. ©2008 ISMP
Brand name medicines appear in green;
generic medicines appear in red.
Dangerous mix-ups between a cancer
medicine and a thyroid medicine
Dangerous mix-ups have occurred
in community pharmacies between
two powerful medicines: propylthiouracil
(pronounced pro-pull-thy-oyour-
a-sill)—a medicine used to
treat an overactive thyroid, and
Purinethol (mercaptopurine)—a
chemotherapy (cancer) medicine
used to treat leukemia.
In one case, a child with leukemia
received 50 mg tablets of propylthiouracil
instead of 50 mg tablets
of Purinethol. The child had taken
Purinethol before for
his cancer, so his parents
told the pharmacist
that the tablets
looked different than
expected. The pharmacist
said the tablets
looked different
because they were
purchased from a different
company. He
reassured the parents
that the prescription
was filled correctly.
The child took the wrong medicine
for 6 months, because the same
mistake happened with the next five
refills. No immediate harm
occurred, but long-term problems
are possible since the child missed
6 months of chemotherapy.
Harm is also likely to occur if prescriptions
for the thyroid medicine
(propylthiouracil) are filled with the
cancer medicine (Purinethol). To
cite one instance, a pregnant
woman with thyroid disease
received a prescription written as
“PTU” 50 mg daily. See a copy of
the actual prescription below. Her
doctor used the common but dangerous
abbreviation of PTU for
propylthiouracil.
The pharmacist thought the abbreviation
stood for Purinethol and
filled her prescription with this
powerful cancer medicine. The
woman did not bring the difference
in appearance between this prescription
and previous prescriptions
to the attention of
the pharmacist. After
5 weeks of taking the
cancer medicine, she
developed a fever, a
painful tear in her
rectum, and vaginal
bleeding. She was
admitted to the hospital
with a serious
infection. (Cancer
medicines often
lessen the ability to
fight off infections.)
The woman, who was 16 weeks
pregnant, lost the baby and required
surgery to deliver the placenta. Her
heart stopped beating during surgery,
and despite multiple attempts
to save her, she died. Her death
remained a mystery until her family
gave her pharmacy prescription
records to the medical examiner.
See Check it out! for ways to help
prevent mix-ups when you pick up
prescriptions from the pharmacy.
the medical examiner.
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