WASHINGTON (AP) - It's the dirty little secret of pediatrics: Unknown to most parents, the majority of drugs prescribed for children have never been tested in youngsters to determine how well they work or even the best dose.

Pediatricians often must guess how to use medications originally developed for adults - from allergy relievers and antibiotics to painkillers - in their tiniest patients.

That's finally changing: Clinical trials of medications in children are suddenly booming, and the Food and Drug Administration expects more than 18,000 youngsters to participate in the next few years.

But how do families pick a safe study? After all, the government recently shut down several adult clinical trials for breaking vital patient-safety rules, including one study that killed an 18-year-old.

Children's studies also broach new ethical questions. Already, researchers are offering enticements like gift certificates to Toys 'R Us to reward kids for getting poked and prodded, and about one-fourth pay families. Typical payments are $200 to $400, but parents have been offered $1,000 to sign up their kids.

Although "we are very excited" that crucial research is finally under way, "there are special issues involved in pediatric trials," stressed FDA pediatrics chief Dr. Dianne Murphy, who is leading efforts to ensure children are studied properly.

Manufacturers have had no incentive to study children because doctors legally can prescribe adult products to youngsters. That changed two years ago when Congress granted manufacturers an extra six months of patent protection if they voluntarily test products pediatricians prescribe.

Then, this December, an FDA rule will mandate that any new adult drug that could be used in children with the same disease must undergo pediatric study.

Some 180 pediatric drug trials have begun or are being planned, and the FDA has requested another 129 even before the December rule kicks in.

"Kids are not just small adults," explained Gregory Kearns, pediatric pharmacology chief at Children's Mercy Hospital in Kansas City, Mo., one of the few places that specializes in testing children's medicines.

Indeed, bodies handle drugs differently at different ages. A tragic example: In the 1960s, several newborns died because doctors didn't know their immature livers couldn't process the adult antibiotic chloramphenicol. In contrast, some of today's antibiotics require a 50 percent higher dose for a 1-year-old than for a teen, because the toddler's body eliminates those drugs faster, Kearns said.

Studies aren't just for sick kids. Say your child is prone to hay fever but is not sniffling today. She'd be a candidate to swallow one dose of an adult antihistamine and have blood samples drawn to check metabolism, thus confirming the right dose. These dosing studies require spending up to a day in a clinic, giving blood and a small side-effect risk, in hopes doctors can improve treatment of future patients.

Longer studies are usually for sick kids, and sometimes involve a placebo. Take the inhaled antibiotic Tobi, approved to treat a lung infection in cystic fibrosis patients at least 6 years old. Taking Tobi before age 6 might ward off the infection instead of just treating it, but it also might be dangerous. Comparing Tobi with a dummy pill in babies and preschoolers is the only way to know, but some parents find that a tough choice, says Dr. Pamela Zeitlin of Baltimore's Johns Hopkins University.

How should parents weigh studies?
-Make sure you fully understand a study. Kearns spends up to an hour discussing a study before ever handing parents a consent form, which should explain risks in laymen's terms.

-Ask who's running the study. University-based research, particularly at pediatric specialty centers, may get more careful oversight.

-Look for pediatric expertise. If your child will test a stomach drug, look for a pediatric gastroenterologist. Adult doctors can miss children's subtle signals of side effects, like not playing or eating less.

-Ask not only about drug side effects but about study procedures. How will doctors minimize blood tests and pain?

Consider the experience of Janine Berardi. The Canton, Mass., woman pored over a 17-page consent form before letting 6-year-old Nichole test an adult immune-system drug called Avonex for her juvenile arthritis. Still she was surprised when Nichole screamed at the weekly injections - until the doctor suggested simply rubbing an anesthetic cream onto her skin before the shots. Now Nichole's swollen joints are much better, and the shots quieter.

Copyright 2000 The Associated Press. All rights reserved.