Which test should be done before starting the Isoniazid therapy to a patient?

Central Institute of Psychiatry - 9 July 2022

Pharmacology

Easy

Appeared in: Central Institute of Psychiatry - 9 July 2022

Explanation

Isoniazid (INH) is a first-line antitubercular drug with a well-documented risk of causing drug-induced liver injury (hepatotoxicity).
A baseline Liver Function Test (LFT) is essential before starting treatment to establish the patient's normal liver enzyme levels, particularly Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST).
This baseline is critical for monitoring. A significant rise in these enzymes during therapy indicates liver damage and may require discontinuation of the drug.
Guidelines recommend stopping INH if ALT levels rise more than three times the upper limit of normal with symptoms, or more than five times without symptoms.

Option B: Serum creatinine measures kidney function. While important for overall health assessment, it is not the specific test to monitor for Isoniazid's primary toxicity.
Option C: A serum electrolyte panel is not routinely required specifically for initiating Isoniazid therapy.
Option D: This option is incorrect because a specific and crucial baseline test (LFT) is the standard of care before starting Isoniazid to ensure patient safety.

Clinical Relevance

Nursing practice connection: Safe nursing care depends on performing Monitoring for adverse effects of antitubercular drugs, specifically Isoniazid-induced hepatotoxicity in the correct sequence, documenting the action clearly, and monitoring for the expected response.
A key nursing responsibility is to educate patients on the signs and symptoms of hepatotoxicity (jaundice, dark urine, nausea, unexplained fatigue, abdominal pain) and to instruct them to report these immediately.
Before administering the first dose of Isoniazid, the nurse must verify that baseline LFTs have been ordered and the results are reviewed, especially for patients with risk factors like alcohol use, pre-existing liver disease, or advanced age.
What if? If a patient's baseline LFTs are already elevated (e.g., ALT is twice the upper limit of normal), the provider may decide to use an alternative, less hepatotoxic TB regimen or proceed with INH but with a plan for more frequent LFT monitoring (e.g., weekly).

How to Approach the Question

First, identify the key drug in the question: Isoniazid (INH).
Recall the major adverse effects associated with this drug. The most critical and well-known side effect of Isoniazid is hepatotoxicity (liver damage).
Next, analyze the options provided. Each option represents a different laboratory test.
Connect the drug's primary adverse effect to the corresponding diagnostic test. Liver damage is monitored using Liver Function Tests (LFTs).
Evaluate the other options to confirm your choice. Serum creatinine assesses kidney function, and serum electrolytes assess metabolic status; neither is the primary test for INH monitoring.
Therefore, LFT is the most logical and correct answer for baseline testing before starting Isoniazid.

Concept Tested & Keywords

Concept Tested: Monitoring for adverse effects of antitubercular drugs, specifically Isoniazid-induced hepatotoxicity.
Stem keywords: Isoniazid therapy, test, before starting
Lead-in keywords: Which test
Negative lead-in flag: false

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E6 Pharmacology Nursing Lilley 11e Part 3 p. 31-33

E6 Medicine Harrison 22e Part 1 pp. 1463-1465, 1461-1463