A 57-year- old lady came with chief complaints of fatigue. On fuher questioning, she reveals that she has gained 5 kg weight in one month. She has been taking L-thyroxine for hypothyroidism since 10 years and fairly controlled. Recently she was staed on an anti-arrhythmic drug for treatment of his cardiac condition. The symptoms staed after sta of this drug. Most likely anti-arrhythmic drug she was prescribed is?

**Core Concept**
The question revolves around the interaction between anti-arrhythmic drugs and thyroid hormone replacement therapy, specifically focusing on the effects of certain medications on thyroid function. **Hypothyroidism** is a condition where the thyroid gland doesn't produce enough thyroid hormones, and **L-thyroxine** is a common replacement therapy. Some medications can interfere with thyroid hormone levels or their action.

**Why the Correct Answer is Right**
Given that the symptoms started after the initiation of the anti-arrhythmic drug, it suggests that the drug is likely interfering with the patient's thyroid hormone levels or their efficacy. **Amiodarone**, an anti-arrhythmic medication, is known to affect thyroid function, leading to both hypothyroidism and hyperthyroidism in different patients due to its high iodine content and direct toxic effects on the thyroid gland.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option provided, we cannot directly address why it is incorrect, but generally, other anti-arrhythmic drugs do not have as significant an impact on thyroid function as Amiodarone.
**Option B:** Similarly, without specifics, it's hard to comment, but if it were a drug like beta-blockers, they are not typically known for causing significant changes in thyroid hormone levels.
**Option C:** Again, lacking specifics, but drugs in other classes might not have the same level of thyroid interference as Amiodarone.
**Option D:** This option is also unspecified, but if it were a drug not known to affect thyroid function, it would be an incorrect choice due to the temporal relationship between starting the drug and the onset of symptoms.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **Amiodarone** can cause thyroid dysfunction, and patients starting on this medication should be monitored for changes in thyroid function, given its high iodine content and potential for thyroid toxicity.

**Correct Answer:** D. Amiodarone.

✓ Correct Answer: B. Amiodarone