Study Shows Methylphenidate Linked to Chromosomal Changes
28 Feb 2005
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 abnormalities-occurrences associated with increased
risks of cancer and other adverse health effects.
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.
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.
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.
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.
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.
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.
“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.
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.
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.”
Parents should respond cautiously to this preliminary study,
El-Zein said, noting that there are few alternatives to
methylphenidate for treating ADHD.
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 wouldn't take him off it” unless
additional studies showed similar effects.
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
ScienceDirect's Cancer Letters page (sciencedirect.com/science/journal/03043835).
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