Some people taking the antibiotic Ketek have experienced liver problems, worsening of a neuromuscular disease and fainting, the drug's manufacturer said in safety update Tuesday.

Ketek, the brand name for telithromycin, is used to treat some types of pneumonia, throat and sinus infections and exacerbation of chronic bronchitis.

The drug's manufacturer, Sanofi-aventis Canada, in consultation with Health Canada, is sending letters to consumers and health professionals warning of:

• Liver problems: There have been rare reports of severe liver injury, which can be life-threatening, in patients using Ketek.
• Worsening of myasthenia gravis: In patients with a neuromuscular disease known as myasthenia gravis, there have been reports of a sudden worsening of symptoms during treatment with Ketek.
• Fainting: Ketek can cause fainting in some patients, especially those who are experiencing severe nausea, vomiting or light-headedness.

The updated safety information follows an advisory from Health Canada in February, which warned people with liver problems not to take the antibiotic after rare cases of severe liver injury were reported, including deaths in isolated instances. 

People taking Ketek who experience any signs or symptoms of liver disease should not take their next dose and call their doctor immediately or go to a clinic, said the company's letter.

The signs and symptoms of liver disease include:

• Loss of appetite.
• Nausea.
• Fatigue.
• Dark urine.
• Pale stools.
• Itching or abdominal pain.

Before using Ketek, people should tell their doctors if they have liver disease or have ever had yellowing of the skin and eyes or dark urine when taking the antibiotic previously. It should not be taken by anyone who has experienced significant liver injury or yellowing of the skin or eyes when taking the drug.

It also should not be used by anyone who has had an allergic reaction to Ketek tablets or similar types of antibiotics such as erythromycin, azithromycin (Zithromax) or clarithromycin (Biaxin).

People who have been prescribed Ketek and are not suffering side-effects should continue taking their medicine unless told to do otherwise by a health-care provider.

Before using Ketek, people should tell their doctors if they have myasthenia gravis or if they fainted after taking any medication, the updated safety information said. There were reports of life-threatening breathing trouble and death among myasthenia gravis patients who were taking Ketek.