BETHESDA, Md -- November 19, 2008 -- In contrast to recent findings, 2 of the most common medications used to treat attention deficit hyperactivity disorder (ADHD) do not appear to cause genetic damage in children who take them as prescribed, according to a new study published online in the Journal of the American Academy of Child and Adolescent Psychiatry.
The researchers looked at 3 measures of cytogenetic damage in white blood cells of each child participating in the study and found no evidence of any changes after 3 months of continuous treatment.
"This is good news for parents," said coauthor Kristine L. Witt, National Institute of Environmental Health Sciences (NIEHS), Bethesda, Maryland. "Our results indicate that methylphenidate- and amphetamine-based products do not induce cytogenetic damage in children."
The researchers involved emphasise that the findings should not be interpreted as final proof of the long-term safety of stimulant drugs for the treatment of ADHD.
"More research and close monitoring of children taking these medications for extended periods of time is needed to fully evaluate the physical and behavioural effects of prolonged treatment with stimulants," said coauthor Scott H. Kollins, PhD, Duke University ADHD Program, Durham, North Carolina, where the study was conducted.
The study included 63 children, aged 6 to 12 years, who met full criteria for ADHD but who had not previously been treated with stimulant medications. Children in the study were divided into 2 groups and treated by a board-certified child psychiatrist with either methylphenidate or with mixed amphetamine salts.
Blood samples were taken before the medication was started to establish baseline values for the cytogenetic measures that were analysed in the study, and a second sample was collected after 3 months of continuous treatment. Of the 63 children, 47 completed the full 3-month treatment schedule.
The researchers found no significant differences between the 2 groups of children with regard to age, gender, race, body weight, height, or ADHD subtype. The groups also showed very similar ADHD symptom levels at initial screening and children in both groups responded equally well to the medication.
The researchers looked at 3 standard indicators of chromosomal damage: structural chromosomal aberrations, micronuclei, and sister chromatid exchanges. "We did not see any significant treatment-related increases in any of these 3 endpoints," said Donald R. Mattison, MD, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland. "These results add to a growing body of evidence that therapeutic levels of these medications do not damage chromosomes."
The study was designed to determine the reproducibility of findings from a previously published paper that reported methylphenidate-induced chromosomal changes in children with ADHD. That paper raised concern for the medical community and parents, given that some of the changes have been associated with an increased risk of cancer.
The current study was not able to replicate the findings from the previous study. The new study extends the literature by using a larger sample size than previous studies, investigating more than one commonly prescribed medication, and providing well-characterised results that can be generalised to other ADHD populations.
"One way scientists evaluate each other's work is by attempting to reproduce the original experiment or study," said Witt. "We designed a study with specific modifications to address issues raised with the original study. Thus, our results are based on a significantly larger number of children who were carefully evaluated using rigourous, accepted standards, which allowed us to produce high-confidence data at the end of our study."
SOURCE: National Institutes of Health
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