**Question:** Adverse effects of INH are all EXCEPT

A. Pancreatitis
B. Hepatitis
C. Neuropathy
D. Haematological toxicity

**Correct Answer:** C. Neuropathy

**Core Concept:**
INH (Isoniazid) is an antibiotic used in the treatment of tuberculosis. Although it is a crucial drug in managing tuberculosis, it can cause various adverse effects due to its pharmacological properties. These effects can be broadly categorized into gastrointestinal, hepatic, hematological, and neurological effects.

**Why the Correct Answer is Right:**
INH primarily acts as an anti-tuberculosis drug by inhibiting the growth of Mycobacterium tuberculosis bacteria. However, it is a pro-drug that gets activated into hydrazine and keto-ester, which leads to its pharmacological effects. Among the listed options, neuropathy is a rare but significant adverse effect. The exact mechanism of neuropathy is not fully understood, but it is believed to be caused by the accumulation of hydrazine and its toxic effects on the peripheral nerves.

**Why Each Wrong Option is Incorrect:**

A. Pancreatitis: Although INH can cause pancreatitis, this effect is not the correct answer as neuropathy is specifically excluded.
B. Hepatitis: Hepatitis is a known adverse effect of INH, but it is not the correct answer because neuropathy is not mentioned.
D. Haematological toxicity: Haematological toxicity includes anemia, leukopenia, and thrombocytopenia, but these effects are not the correct answer, as they are not mentioned in the question as adverse effects to be excluded.

**Clinical Pearl:**
It is essential for healthcare professionals to be aware of the adverse effects of INH, including neuropathy, to promptly identify and manage them in patients undergoing tuberculosis treatment. Understanding the pharmacokinetics and pharmacodynamics of INH and its active forms can help differentiate between common adverse effects and those to be excluded in this question.