E-drug: Methylphenidate (2)
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Dear Naziruddin Ahsan,
Reference the recent query on the above subject, I reproduce below a news
article published in the American Journal of Health-System Pharmacy Vol.53
March 15, 1996 p. 610:
"Methylphenidate studies give 'weak signal' of carcinogenic potential
The labeling for methylphenidate drug products has been modified to
include findings of two two-year carcinogenicity studies conducted by the
National Toxicological Program of the U.S. Department of Health and Human
Services. FDA [Food and Drug Administration] regards the findings of the
studies as a "weak signal" that the drug may have carcinogenic potential.
FDA still considers methylphenidate a safe and effective drug but stated
that the signal "indicates a potential risk that needs to be considered
and further studied because of the increasing and
often long-term use of [methylphenidate] in children." The agency said
that use of the drug had increased two-to three-fold in the past five
years. The carcinogenicity studies were recommended by the National Cancer
Institute because such studies of methylphenidate had not been performed.
The National Toxicological Program studies showed no evidence of
carcinogenicity in rats. In mice, methylphenidate was associated with an
increase in benign hepatocellucalr adenomas and, in males only, an
increase in a rare malignant tumor (hepatoblastoma) at a dose of 60
mg/kg/day (about 30 times the recommended human dose expressed as
milligrams per kilogram of body weight and 2.5 times the dose expressed as
milligrams per square meter of body surface area).
FDA considers the results a weak signal for several reasons. The increased
rate of tumor formation was seen in one, not both, of the rodent species
tested and in only one organ, the mouse liver, which is known to be
sensitive to tumor development in response to various stimuli. The
increased rate primariliy involved nonmalignant tumors, and there was no
increase in animal mortality rate. Furthermore, the type of tumor detected
is rare in humans, and no increase in incidence has been seen in recent
years despite increased use of methylphenidate. According to Ciba-Geigy
(manufacturer of Ritalin), other drugs perceived to be safe in humans
(e.g., phenobarbital, carbamazepine, and metronidazole) have stronger
signals of carcinogenicity.
FDA is planning followup tests in animals, as well as epidemiologic
studies in humans."
I hope the above is useful. If you need any further information or would
like to receive copies of the studies, please contact me. Thanks.
Syed Rizwanuddin Ahmad
Washington, DC
Email: srahmad@essential.org
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