The study showed that a pyridine moiety that is part of the telithromycin molecule acts as an antagonist on cholinergic receptors located in the neuromuscular junction, the ciliary ganglion of the eye and the vagus nerve innervating the liver.

Other macrolides, such as azithromycin and clarithromycin and the fluoroketolide, solithromycin, do not contain the pyridine moiety and do not antagonize these cholinergic receptors significantly.

Telithromycin binds to the subunit 50S of the bacterial ribosome,[8] and blocks the progression of the growing polypeptide chain.

Telithromycin fulfills a role that has arisen due to the rise of microbial resistance to existing macrolides and appears to be effective against macrolide-resistant Streptococcus pneumoniae.

French pharmaceutical company Hoechst Marion Roussel (later Sanofi-Aventis) began phase II/III clinical trials of telithromycin (HMR-3647) in 1998.

FDA staffers publicly complained that safety problems and some data integrity issues were ignored prior to approval, and the House Committee on Energy and Commerce held hearings to examine these complaints.

[11] Study 3014 was a key clinical trial of approximately 24,000 patients which Sanofi-Aventis submitted to the FDA to seek approval for Ketek.

The doctor who treated the most patients in Study 3014 (about 400), Maria "Anne" Kirkman Campbell, served a 57-month sentence in federal prison after pleading guilty to mail fraud, by defrauding Aventis and others.

[12] Documents, including internal Sanofi-Aventis emails show that Aventis was worried about Campbell early in study 3014 but didn't tell the FDA until the agency's own inspectors discovered the problem independently.

In July 2006, according to the New York Times, unpublished e-mails from FDA safety official David Graham argued telithromycin had not been proven safe, that safer drugs were available for the same indications, and that the approval was a mistake and should be immediately withdrawn.

On February 12, 2007, after an advisory committee discussion and vote in December 2006, the FDA announced a revision to the labeling of Ketek.