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.
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