The U.S. House of Representatives approved a bill on Wednesday that aims to strengthen government oversight of dangerous side effects from prescription drugs.

On a 405-7 vote, the House backed the measure which emerged earlier in the day from negotiations with a group of Senators. It now goes to the Senate floor where it is expected to pass before heading to President George W. Bush for his signature into law.

The bill gives the Food and Drug Administration the power to require new warnings on prescription drugs that are already on the market and to order the completion of post-approval studies of medicines. Companies that fail to comply with FDA safety directives could face fines of up to $10 million.

The new authority for the FDA is a response to serious problems that emerged in patients who took Merck & Co Inc's withdrawn arthritis drug Vioxx and other medicines.

Critics said the FDA was too slow to respond to signs of problems with Vioxx, which was linked to heart attacks and strokes, as well as risks associated with antidepressants and other drugs.

Lawmakers decided the agency needed clearer authority to compel drugmakers to add new warnings or finish important safety studies.

"This legislation would significantly improve our postmarket safety programs, thereby preventing many of the drug and device injuries and deaths that occur today," said House Energy and Commerce Committee Chairman John Dingell, a Michigan Democrat.

The measure also extends for five years and increases the fees that drug and medical device makers pay to help fund product reviews. It includes an FDA and industry plan for pharmaceutical companies to pay nearly $393 million in fiscal 2008, that begins October 1, an increase of about $87 million from current levels.

Drugmakers would pay an additional $225 million over five years for FDA safety monitoring once drugs reach the market.

In addition, drugmakers must post basic results for clinical trials of approved products in a public database. Companies also must list all clinical trials, except preliminary studies, in the database.

The bill also preserves a six-month period of additional market exclusivity for drugmakers that test the safety and effectiveness of products in children. An earlier Senate version of the bill had cut that time to three months for blockbuster drugs.

(Reporting by Lisa Richwine)