Who should not take Ketek?

People with myasthenia gravis should absolutely not take Ketek; the side effects can be extremely severe and possibly fatal. You should also avoid Ketek if you have a history of liver problems. Other potential conditions that affect the use of Ketek include: kidney disease, low potassium or magnesium or heart problems, such as abnormal rhythm or long QT syndrome. The effects of Ketek on pregnant women and developing fetuses are not known. You should be cautious about taking Ketek if you have ever had an allergic reaction to other antibiotics.