- In a small but startling preliminary new study, Texas
researchers have found that after just three months, every one of a dozen
children treated for attention deficit/hyperactivity disorder (ADHD) with
the drug methylphenidate experienced a threefold increase in levels of
chromosome abnormalitiesóoccurrences associated with increased risks
of cancer and other adverse health effects.
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- The researchers say that to their knowledge this is the
first study addressing the potential chromosome-breaking effects associated
with treatment of children with methylphenidate, the generic name for a
group of drugs that includes Ritalin, Concerta, Metadate CD and others.
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- Methylphenidate is the most widely prescribed of a class
of amphetamine-like drugs used to treat ADHD, with more than 10 million
prescriptions written for it in 1996 alone. Between 1991 and 1999, United
States sales of methylphenidate increased more than 500 percent.
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- Researchers at The University of Texas M.D. Anderson
Cancer Center in Houston and the University of Texas Medical Branch at
Galveston (UTMB) reported their detection of the chromosome abnormalities
in the journal Cancer Letters. Their peer-reviewed paper is to be published
several months hence, but the journal editors have made it available online
in the journal's "articles in press" section.
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- The authors said they undertook the study because, even
though methylphenidate has been approved for human use for more than 50
years, "there are surprisingly few studies" in either animals
or human beings "on the potential for serious side effects,"
such as causing mutations and cancer. In 1996, a report discussing several
two-year-long animal studies showed that the highest levels of methylphenidate
tested caused liver tumors in male and female mice. However, similar studies
in rats showed no such tumors.
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- The new Texas study involved researchers drawing blood
from children diagnosed with ADHD before they began taking methylphenidate
in order to get a baseline level of chromosomal abnormalities. Three months
after the children had begun taking the drug, the researchers drew the
children's blood and tested it a second time. Chromosomes are the bodies
within cells that carry the genes and genetic information. All 12 of the
children whose before-and-after blood cells were studied were treated with
normal therapeutic doses of methylphenidate.
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- Most of the abnormalities found in the studied blood
cells consisted of chromosome breaks "and a higher frequency of aberrations
is reported to be associated with an increased risk of cancer down the
line," said lead author Randa A. El-Zein, M.D., Ph.D., an assistant
professor of epidemiology at M.D. Anderson who performed the blood studies
using several techniques.
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- "It was pretty surprising that all of the children
taking methylphenidate showed an increase in chromosome abnormalities in
a relatively short period of time," El-Zein said.
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- UTMB Professor of Environmental Toxicology Marvin Legator,
the study's principal investigator and senior author, cautioned, "This
study doesn't mean that these kids are going to get cancer, but it does
mean they are exposed to an additional risk factor, assuming that this
study holds up." Of the 53 known human carcinogens, Legator said 48
could be detected using the chromosome analysis methods employed in this
study.
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- El-Zein stressed that much larger studies at several
medical centers are needed to confirm the results of this study and to
answer other questions not addressed by it. One of these issues is the
question of what happens when patients stop taking methylphenidate. "Do
the levels of chromosome abnormalities go back to normal?" El-Zein
said. "We don't know."
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- Parents should respond cautiously to this preliminary
study, El-Zein said, noting that there are few alternatives to methylphenidate
for treating ADHD.
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- Asked what he would do in response to the study if his
child were on methylphenidate, co-author Matthew J. Hay, a UTMB pediatrician
who treated all the children who participated in the study, was equally
guarded. "Twelve kids with one physician in one county is too small
a sample to base a decision on," he said. "If my child were on
the medication and were doing well, I wouldnít take him off it"
unless additional studies showed similar effects.
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- - The Cancer Letters article by Randa A. El-Zein, Sherif
Z. Abdel-Rahman, Matthew J. Hay, Mirtha S. Lopez, Melissa L. Bondy, Debra
L. Morris and Marvin S. Legator can be found on the Web by clicking the
"Articles in Press" button on ScienceDirectís Cancer Letters
page (http://www.sciencedirect.com/science/journal/03043835).
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- © 2005 Newswise. All Rights Reserved.
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- http://www.newswise.com/articles/view/510069/
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