The FDA has strengthened its warnings on the controversial antibiotic Ketek and banned the drug's use for treatment of sinusitis and bronchitis. The new move follows a yearlong FDA investigation into the drug's side effects. The use of the drug will still be permitted for pneumonia.

The FDA investigation began after a scandal broke out over severe liver complications that led to the deaths of five Ketek patients. The deaths sparked a Senate Finance Committee investigation into whether faulty data and fraud were used in the FDA's approval process for the drug.

Under the FDA's new rules, Ketek will carry a "black box" warning against its use by patients with the neuromuscular disorder myasthenia gravis. The "black box" warning -- so called because of the thick black border used to make it stand out -- is the strongest warning that the FDA can put on a drug. Any stronger concerns about a drug's safety require that it be banned.