The first single-dose form of the drug most widely used to treat attention deficit disorder in children won U.S. government approval yesterday.

The Food and Drug Administration said it has approved Concerta for the treatment of attention deficit hyperactivity disorder. Between 4 percent and 12 percent of school-age children – an average of about 2.5 million, mostly boys – are believed to have ADHD. Symptoms include short attention span, impulsive behavior and difficulty focusing and sitting still. Methylphenidate – best known under the name Ritalin – often is prescribed to increase a child's alertness. But current forms of the drug require two or three doses daily, often requiring youngsters to break up their school days with visits to the nurse's office. The new drug lasts 12 hours, which will avoid in-school and after-school dosing. Concerta was developed by Crescendo Pharmaceuticals Corp. and will be manufactured and marketed by ALZA Corp. of Mountain View, Calif. The new form of the drug will eliminate the stigma of taking a drug in school and the problems of getting it to the school nurse or interrupting after-school programs or practice, said Dan Swisher, vice president of ALZA.