| FOR IMMEDIATE RELEASE Sept. 18, 2003, 9:00 a.m. EDT |
For more information, please contact the ATA at thyroid@thyroid.org. |
Combination of Two Drugs Found Superior to Standard Therapy in Reducing Effects of Radiation Exposure if Treatment Is Delayed
(PALM BEACH, FLA., Sept. 18, 2003) - The combination of two thyroid drugs,
Thyrogen® and methimazole, may be a better option for reducing the
effects of radiation exposure to the thyroid gland compared to the current
standard agent, potassium iodine, when treatment is delayed for eight
or 24 hours after exposure, according to a study reported today at the
75th Annual Meeting of the American Thyroid Association.
Studies of populations exposed to fallout from the 1986 Chornobyl nuclear
reactor accident have shown that the thyroid gland is at high risk for
developing cancer after being exposed to this form of radiation. Reducing
the radiation dose to the thyroid after exposure can decrease the cancer
risk, with the highest levels of radiation posing the greatest danger.
Researchers at the University of Würzburg in Würzburg, Germany,
studied 42 healthy adult volunteers. After intake of very small amounts
of the radioactive isotope, iodine-125, the radiation dose reduction of
six treatment regimens was compared. The volunteers were divided into
six similar groups, and each treatment category was assigned to two groups,
at either eight or 24 hours. The treatments were "non-radioactive"
iodine alone; Thyrogen alone; and Thyrogen plus methimazole, followed
by additional methimazole on each of the next two days. A seventh, control
group of volunteers received iodine-125 but no treatment.
Iodine is a trace element, and methimazole is a drug widely used to treat
hyperthyroid disorders. Both agents were taken orally, in doses of 100
mg and 90 mg, respectively. Thyrogen is a genetically engineered form
of human thyroid-stimulating hormone, a naturally occurring substance,
often used in thyroid cancer patients undergoing testing. It was given
in a single intramuscular injection of 0.9 mg.
The Würzburg investigators chose iodine-125 intake to represent accidental
or intentional radiation exposure because the isotope has a relatively
long life in the body, allowing measurement of radiation levels over time.
Using a thyroid probe and computer modeling, the investigators calculated
the average total radiation dose from 24 hours through six weeks after
iodine-125 ingestion in each treatment group and in the untreated group.
Among patients starting treatment eight hours after exposure, the average
radiation dose reduction compared to the untreated group was 63 percent
for the Thyrogen plus methimazole group versus 49 percent for the iodine
group and 33 percent for the Thyrogen alone group. Among patients starting
treatment 24 hours after radiation exposure, the reduction was 42 percent
for the Thyrogen plus methimazole group versus 28 percent for the Thyrogen
alone group and 16 percent in the iodine group. The investigators speculate
that the Thyrogen "squeezes out" the radioactive iodine from
the thyroid tissue and that the methimazole prevents that tissue from
taking it up again.
"Previously, we have shown that the greatest radiation dose reduction
-almost 90 percent- is achieved by giving iodine either prior to or up
to two hours after radiation exposure," stated Markus Luster, MD,
one of the lead investigators of the Würzburg group and assistant
professor in the Department of Nuclear Medicine. "However, in the
real world, treatment might be delayed for several hours or longer. Our
results are preliminary and need to be confirmed in a larger, randomized
study that includes a statistical comparison of the treatment groups.
Although radiation dose reduction decreases the longer treatment is delayed,
our results suggest that an effective option, Thyrogen plus methimazole,
exists even in cases of a 24 hour delay."
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