WASHINGTON (AP) - The first single-dose form of the drug most widely used to treat attention deficit disorder in children won government approval Tuesday.

The Food and Drug Administration said it had 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 schooldays 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.

"It makes the condition private. It eliminates the embarrassment for children," he said in a telephone interview.

Swisher said McNeill Consumer Healthcare is assisting in the marketing of Concerta, which should be available in two weeks. He said the price has not been determined but will be comparable to other ADHD treatments.

Typically, people suffering from ADHD have problems following instructions and paying attention. They may seem not to listen; be disorganized; miss details; have trouble starting tasks, or performing tasks that require planning or long-term effort; appear to be easily distracted or forgetful. In many cases they seem "hyper," being fidgety, impulsive and unable to wait their turn.

Not all people with the disorder exhibit all the symptoms all the time.

Many of the symptoms also are associated with youthful rambunctiousness, which has raised questions whether today's youngsters are being overdiagnosed and overdrugged.

As a result, the American Academy of Pediatrics issued in May its first guidelines for ADHD, hoping to eliminate incorrect diagnoses and ensure untreated children get the help they need.

The guidelines are for children 6 through 12. Most ADHD research has involved that age group.

Concerta is an extended-release formula in tablet form designed to be taken in the morning before a child leaves for school.

In clinical trials the most common side effects were headaches, reported by 14 percent of patients. Less common were upper respiratory tract infection and stomachache.

Copyright 2000 The Associated Press. All rights reserved.