Newswise — 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 (http://www.sciencedirect.com/science/journal/03043835).
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Cancer Letters (forthcoming)