From the Guidelines
For patients on isoniazid, baseline and periodic monitoring should include liver function tests (LFTs) such as ALT, AST, bilirubin, and alkaline phosphatase, especially in those with pre-existing liver disease, HIV infection, or regular alcohol use, as recommended by the most recent guidelines 1.
Monitoring Parameters
- Liver function tests (LFTs): ALT, AST, bilirubin, and alkaline phosphatase, typically at baseline and then monthly for the first three months, followed by periodic testing for the duration of therapy
- Complete blood count (CBC) to monitor for potential hematologic effects like anemia or thrombocytopenia
- Renal function tests (BUN, creatinine) to assess kidney function, especially in patients with pre-existing renal disease
- Vitamin B6 (pyridoxine) levels may be monitored in high-risk patients, as isoniazid can deplete this vitamin and cause peripheral neuropathy
Special Considerations
- Patients with pre-existing liver disease, HIV infection, or regular alcohol use require more frequent monitoring of LFTs, as recommended by the guidelines 1
- Discontinue isoniazid if serum AST concentration is ≥5 times the upper limit of normal in the absence of symptoms or ≥3 times the upper limit of normal in the presence of symptoms, as per the guidelines 1
- Monthly evaluations to assess treatment adherence and adverse effects, with repeated patient education regarding adverse effects at each visit, are crucial for patient safety 1
From the FDA Drug Label
The risk of hepatitis is increased with daily consumption of alcohol Precise data to provide a fatality rate for isoniazid-related hepatitis is not available; however, in a U. S. Public Health Service Surveillance Study in- volving 13,838 persons taking isoniazid, there were 8 deaths among 174 cases of hepatitis. Therefore, patients given isoniazid should be carefully monitored and interviewed at monthly intervals For persons 35 and older, in addition to monthly symptom reviews, hepatic enzymes (specifically, AST and ALT (formerly SGOT and SGPT, respectively)) should be measured prior to starting isoniazid therapy and periodically throughout treatment. Because there is a higher frequency of isoniazid associated hepatitis among certain patient groups, including Age > 35, daily users of alcohol, chronic liver disease, injection drug use and women belonging to minority groups, particularly in the post-partum period, transaminase measurements should be obtained prior to starting and monthly during preventative therapy, or more frequently as needed.
The labs to check for a patient on isoniazid are:
- Hepatic enzymes:
- AST (formerly SGOT)
- ALT (formerly SGPT) These labs should be measured:
- Prior to starting isoniazid therapy
- Periodically throughout treatment
- Monthly during preventative therapy, or more frequently as needed, especially for patients with increased risk of hepatitis, such as those over 35 years old, daily users of alcohol, or those with chronic liver disease 2, 2.
From the Research
Laboratory Tests for Patients on Isoniazid
To monitor patients on isoniazid, several laboratory tests are recommended:
- Complete blood cell count with platelets 3
- Blood glucose and lipid profile 4
- Liver function tests, including:
- Hepatitis B surface antigen and hepatitis C antibody 4, 3, 6
- Serum albumin, iron, total iron-binding capacity, and ferritin 4, 3, 6
- Prothrombin time 3
Rationale for Laboratory Tests
These laboratory tests are recommended to monitor for potential hepatotoxicity associated with isoniazid use 5, as well as to evaluate underlying liver disease 4, 3, 6. The tests can help identify patients at risk for liver-related mortality and guide further evaluation and management 6. Additionally, the tests can help assess the severity of liver injury and guide the need for additional testing or referral to a hepatologist 4, 3, 6.