Blood Test May Curb Liver Damage from TB Drug

NEW YORK (Reuters Health) - Measuring blood levels of a enzyme called AST may help prevent the liver damage that often occurs with isoniazid, a drug used to treat tuberculosis, researchers report in the medical journal Chest.

AST, short for aspartate aminotransferase, is produced by a variety of cells in the body, particularly liver cells. When AST levels rise in the blood, it can suggest that the liver has been damaged in some way.

Dr. Timothy Self of the University of Tennessee Health Science Center, Memphis and colleagues note that the side effects of such therapy can range from mild transient elevations in AST to rare cases of liver inflammation or hepatitis.

To determine the overall rate of isoniazid-related liver damage, the researchers analyzed data from a public health department TB clinic obtained over a 7-year period. This covered 3,377 patients who were 25 years or older.

On starting therapy, 19 patients had AST levels more than 5.3 times the upper limit of normal. Thus, in a group of 1,000 patients, 5.6 would have this finding.

After one month of treatment, the number of AST elevations per 1000 patients was 2.75. Corresponding numbers at three and six months of therapy were 7.20 and 4.10.

These events were more common in older patients. In patients 34 year of age or younger, the rate was 4.40 per 1,000. For patients age 35 to 49 years, it was 8.54. For older patients, it was 20.83.

Age and AST levels above the upper limit of normal before treatment were risk factors for liver damage during follow-up.

The researchers note that this and earlier reports "confirm that serious (liver damage) can occur" in patients without any symptoms.

Given these findings, the team concludes that limited monitoring of AST levels in all patients over the age of 35 and those with other risk factors is appropriate.

SOURCE: Chest, July 2005.