Delayed-release Ritalin has less potential for abuse

NEW YORK (Reuters Health) - A once-daily, controlled-release formulation of Ritalin, also known by its generic name methylphenidate, to treat attention-deficit hyperactivity disorder (ADHD) may be less likely to lead to abuse than the traditional immediate-release methylphenidate.

Dr. Thomas J. Spencer from Massachusetts General Hospital and Harvard Medical School in Boston and colleagues compared the abuse potential of immediate-release and controlled-release methylphenidate in 12 healthy adult volunteers. None had been diagnosed with ADHD or any neurological or psychiatric disorder.

Using positron emission tomography (PET) scans, which measure dopamine transporter blockade, the investigators found that a 90-mg capsule of controlled-release methylphenidate produced the same dopamine blockade in the brain as a 40-mg capsule of immediate-release methylphenidate, although at a much slower rate.

Although the two formulations led to similar concentrations in the blood, controlled-release methylphenidate required a longer period of time to reach peak blood and brain levels and to block the dopamine transporter in the brain.

Unlike the immediate-release methylphenidate, the subjects reported no preference and detected no subjective effects with the controlled-release methylphenidate.

"The findings suggest that the abuse potential of oral methylphenidate is strongly influenced by the rate of delivery and not solely by the magnitude of plasma concentrations or brain transporter occupancy," the authors conclude.

"These results," they add, "advance understanding of the underlying central effects of methylphenidate in humans and identify a potentially less abusable methylphenidate formulation."

The study was funded by a grant from the National Institute of Mental Health and McNeil Consumer and Specialty Pharmaceuticals.

SOURCE: American Journal of Psychiatry, March 2006.