[U.S. Food and Drug Administration]

FDA Medical Bulletin * January 1996 * Volume 26 Number 1

Labeling Change

Labeling for products containing chlorzoxazone [McNeil's Paraflex (250mg) and Parafon Forte DSC (500mg) and many generics] has recently been revised to strengthen the hepatotoxicity warnings.

The new warning language is shown below:

Serious (including fatal) hepatocellular toxicity has been reported rarely in patients receiving chlorzoxazone. The mechanism is unknown but appears to be idiosyncratic and unpredictable. Factors predisposing patients to this rare event are not known. Patients should be instructed to report early signs and/or symptoms of hepatotoxicity such as fever, rash, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, or jaundice. Chlorzoxazone should be discontinued immediately and a physician consulted if any of these signs or symptoms develop. Chlorzoxazone use should also be discontinued if a patient develops abnormal liver enzymes (e.g., AST, ALT, alkaline phosphatase, and bilirubin).

The concomitant use of alcohol or other central nervous system depressants may have an additive effect.

REPORT SERIOUS ADVERSE EVENTS AND PRODUCT PROBLEMS TO MEDWATCH
1-800-FDA-1088

[Table of Contents] [FDA HOME PAGE]