What is a Ketek?: The Ketolide Antibiotic with a Controversial Past

October 11, 2025 •

3 min read

First approved in 2004, Ketek (telithromycin) was a new class of antibiotic known as a ketolide, designed to combat resistance to older macrolide drugs. However, its history was marked by significant safety concerns, especially related to serious and sometimes fatal liver damage, which ultimately led to its removal from the market.

Quick Summary

An exploration of Ketek (telithromycin), a discontinued ketolide antibiotic. Learn about its original use for respiratory infections, its mechanism of action, the serious adverse events that led to FDA warnings, and its eventual withdrawal.

Key Points

Ketek's Class: Ketek, or telithromycin, is a ketolide antibiotic, a synthetic variation of the macrolide class designed to combat bacterial resistance.
Inhibits Protein Synthesis: It works by binding to bacterial ribosomes, effectively stopping the production of proteins essential for bacterial growth.
Serious Liver Damage: The drug was famously associated with a high risk of severe hepatotoxicity, leading to acute liver failure in some cases.
Risk for Myasthenia Gravis: It was explicitly contraindicated for patients with myasthenia gravis, due to reports of fatal respiratory failure.
FDA Warnings and Restrictions: Following a congressional investigation and reports of severe side effects, the FDA added a black box warning and restricted its approved uses.
Fraudulent Clinical Trial Data: A significant controversy surrounded its approval process, involving falsified data submitted during a key clinical trial.
Discontinued in the US: Due to the severe safety issues and a reassessment of its risk-benefit profile, the manufacturer discontinued Ketek in 2016.

Ketek's Rise as a Ketolide Antibiotic

Ketek, with the active ingredient telithromycin, was developed by the pharmaceutical company Sanofi-Aventis. It was introduced as the first in a new class of antibiotics called ketolides. Ketolides are a semi-synthetic variation of macrolide antibiotics, like erythromycin, and were designed to overcome bacterial resistance that had emerged against older macrolides.

Telithromycin's novel structure gave it an advantage over its predecessors. By replacing the neutral sugar of the macrolide ring with a keto group, it was made less susceptible to common resistance mechanisms. Furthermore, its binding affinity to the bacterial ribosome was significantly stronger, allowing it to inhibit protein synthesis more effectively.

Upon its US Food and Drug Administration (FDA) approval in 2004, Ketek was initially indicated for treating a range of upper and lower respiratory tract infections in adults. These included mild to moderate community-acquired pneumonia (CAP), acute bacterial sinusitis (ABS), and acute bacterial exacerbation of chronic bronchitis (AECB).

The Serious Adverse Effects and FDA Action

Shortly after its introduction, reports of severe adverse drug reactions began to emerge, casting a shadow over Ketek's perceived benefits. These reports highlighted a pattern of serious side effects that had not been adequately addressed during the pre-approval phase, partly due to fraudulent data in one of the key clinical trials.

Liver Toxicity (Hepatotoxicity)

One of the most alarming side effects linked to Ketek was severe liver toxicity, or hepatotoxicity. In some cases, this resulted in acute liver failure, with some patients requiring liver transplants or dying. This liver injury could occur rapidly, sometimes after only a few doses. Symptoms of liver damage included:

Nausea and fatigue
Jaundice (yellowing of the skin and eyes)
Dark urine and light-colored stools
Abdominal pain and swelling (ascites)

Exacerbation of Myasthenia Gravis

Another fatal risk associated with Ketek involved patients with myasthenia gravis, a neuromuscular disease that causes muscle weakness. Case reports documented fatal and life-threatening respiratory failure in this patient population, sometimes within hours of the first dose. This was later understood to be due to telithromycin's off-target effect on cholinergic receptors.

Visual and Neurological Disturbances

Patients also reported transient vision problems, including blurred vision, difficulty focusing, and double vision. Other neurological effects included dizziness, lightheadedness, and fainting, which could impact a person's ability to drive or operate machinery.

FDA Restrictions and Drug Discontinuation

In response to mounting evidence of these serious side effects and a congressional investigation into the drug's approval process, the FDA took action. In 2007, the agency severely curtailed Ketek's indications, removing ABS and AECB from its approved uses. The drug's label was also updated with a prominent black box warning, the FDA's strongest warning, explicitly stating its contraindication in patients with myasthenia gravis.

Following these restrictions and continued safety concerns, the manufacturer, Sanofi-Aventis, ultimately discontinued Ketek for business reasons in 2016, and it is no longer available in the United States.

Comparing Ketek (Telithromycin) to Macrolide Antibiotics


Feature	Ketek (Telithromycin)	Macrolide Antibiotics (e.g., Azithromycin)
Drug Class	Ketolide	Macrolide
Targeted Bacteria	Effective against strains resistant to macrolides	Effective against various bacteria, but resistance is common
Mechanism	Binds more strongly to two sites on the 50S ribosomal subunit	Binds to one site on the 50S ribosomal subunit
Acid Stability	Stable in acid; better oral bioavailability	Variable stability; erythromycin is acid-labile
Main Use	Historically: Community-acquired pneumonia	Widely used for respiratory, skin, and STIs
Safety Profile	Higher risk of serious hepatotoxicity, myasthenia gravis exacerbation, and vision issues	Generally safer; hepatotoxicity and QT prolongation can occur but are rarer and less severe
Status	Discontinued in the US	Widely available

Conclusion

Ketek's trajectory from a promising, new-generation antibiotic to a cautionary tale of drug safety and market withdrawal serves as an important lesson in pharmacology. While its development as a ketolide offered an innovative approach to combatting macrolide-resistant bacteria, the serious and often fatal adverse effects, particularly related to liver damage and myasthenia gravis, highlighted critical gaps in its clinical trials and post-market surveillance. The FDA's eventual actions—restricting its use and mandating a black box warning—marked a significant regulatory response. Today, Ketek (telithromycin) is no longer available for prescription, with safer, more effective alternatives filling its former role. Its history underscores the importance of stringent drug safety testing and transparent reporting throughout the entire development and approval process. For further information on the telithromycin controversy and its mechanism of action, readers can consult resources like the Wikipedia page on Telithromycin.

Frequently Asked Questions

No, Ketek (telithromycin) was discontinued by its manufacturer, Sanofi Aventis, in 2016 for business reasons and is no longer available for prescription in the United States.

Ketek was discontinued primarily due to severe safety concerns, including reports of fatal liver failure and life-threatening respiratory failure in patients with myasthenia gravis. The FDA severely restricted its use before it was ultimately removed from the market.

The primary risk associated with Ketek is hepatotoxicity, or severe liver damage, which could lead to acute liver failure and sometimes death. Vision problems and exacerbation of myasthenia gravis were also serious risks.

Ketek is a ketolide antibiotic, a specific class related to macrolide antibiotics like erythromycin and azithromycin.

Yes, Ketek was initially approved by the FDA in 2004 for several respiratory infections. However, the FDA later restricted its uses and issued its strongest "black box warning" due to serious safety issues.

Before FDA restrictions, Ketek was approved for mild to moderate community-acquired pneumonia, acute bacterial sinusitis, and acute bacterial exacerbation of chronic bronchitis in adults.

Yes, a congressional investigation revealed that fraudulent data was used in a key clinical trial submitted for Ketek's approval. The doctor involved later pleaded guilty to mail fraud.