Which laboratory tests are used to monitor hepatotoxicity risk when taking isoniazid?

• A. Creatinine.
• B. Amylase.
• C. ALT and AST.
• D. Bilirubin.

Answer: (C)

Monitoring for liver injury while taking isoniazid hinges on measuring liver enzymes that indicate hepatocellular damage. Isoniazid can cause hepatotoxicity, sometimes without symptoms, so catching rises in these enzymes early is crucial. Alanine aminotransferase (ALT) is more specific to the liver, and aspartate aminotransferase (AST) rises with hepatocyte injury as well. Together, ALT and AST provide a sensitive signal that the liver is being affected, making them the best tests for this purpose. Baseline levels before starting therapy and periodic monitoring during treatment help detect toxicity early and guide decisions about continuing, adjusting, or stopping the drug if elevations occur.

Other tests don’t target liver cell injury as directly. Creatinine assesses kidney function, amylase points to the pancreas, and bilirubin can indicate bile flow problems or more advanced liver dysfunction but isn’t as sensitive for early hepatocellular injury.