There aren't nearly enough medications that have been tailored to the needs of children, the World Health Organization said Thursday as it launched a global campaign to promote more research into child medicine.

The WHO says more than half the drugs currently used to treat children in the industrialized world have not been specifically tested on kids. That kind of research is crucial, the United Nations agency says, because children metabolize medicines differently from adults.

What's more, children need alternative ways of taking pharmaceuticals because they may not be able to swallow a large pill or tolerate painful injections.

Not all adult medicines are palatable to children. For example, zinc is an effective treatment for diarrhea in children, but children generally don't like the tablet and refuse to take it, and they often dislike syrups too.

What's needed is solid-dose formulations that a child can swallow without tasting, says Dr. Suzanne Hill, a scientist from WHO's Policy, Access and Rational Use team.

"We know they work, they're on the essential medicines list, but we need to have a dose and a formulation that is palatable to children," she said earlier this year. "And we need a manufacturer who will make that and do so at a reasonable price."

Medications need to be better tailored for youngsters to tackle illnesses such as pneumonia and diarrhea that claim millions of lives every year, the WHO said. Children in both the industrialized and the developing world would benefit from more research in this area, the agency says.

"The gap between the availability and the need for child- appropriate medicines touches wealthy as well as poor countries,'' said Margaret Chan, WHO director-general, in a statement.

"As we strive for equitable access to scientific progress in health, children must be one of our top priorities."

In a bid to address the problem, the WHO has drawn up its first international List of Essential Medicines for Children. The list contains 206 medications deemed safe for children that tackle priority conditions.

Those conditions include pneumonia, HIV/AIDS, malaria, diarrhea and tuberculosis. Those five conditions are responsible for more than half of the deaths of children under the age of five, the agency says. Most of those deaths could have been prevented with medication.

In the case of HIV/AIDS, the few existing therapies that have developed for children generally cost three times more than adult ones, the WHO notes.

It would like to see more medications for treating HIV, as well as child-tailored antibiotics, asthma medications and pain relievers.

Testing medicines on children has always been a difficult issue. That's because volunteers in clinical trials need to consent that they understand that the study they are participating in contains risk. Getting that kind of consent from children is not easy.

As a result, drug companies have been wary of developing child-friendly medicines.

In an attempt to tackle the issue, European lawmakers introduced legislation this year that requires drug companies seeking approval for new medicines to include research data for products that may benefit young patients.

U.S. legislators passed similar rules 10 years ago.