**Question:** Fixed drug eruptions can be seen more frequently with

A. Aminoglycosides
B. Nonsteroidal anti-inflammatory drugs (NSAIDs)
C. Beta-lactam antibiotics
D. Antiepileptic drugs

**Core Concept:** Fixed drug eruptions (FDE) are a type of drug reaction characterized by a specific, recurrent, and non-progressive skin lesion, occurring at the same site upon re-exposure to the causative drug.

**Why the Correct Answer is Right:** Fixed drug eruptions are primarily caused by sensitization of the skin to a specific drug. In the case of D, antiepileptic drugs, this sensitization occurs due to the formation of a hapten, which is a small molecule that binds covalently to proteins in the skin, leading to an immune response. This immune response results in an increased sensitivity to the haptenated drug molecules, causing an FDE upon re-exposure.

**Why Each Wrong Option is Incorrect:**

A. Aminoglycosides: Fixed drug eruptions are less commonly associated with aminoglycosides compared to other drug categories. Aminoglycosides are antibiotics that primarily affect the respiratory and urinary tract infections.

B. Nonsteroidal anti-inflammatory drugs (NSAIDs): Although FDE can occur with NSAIDs, the frequency is higher for the antiepileptic drug category (D). NSAIDs are a diverse group of medications used for pain relief, inflammation, and fever reduction.

C. Beta-lactam antibiotics: FDE are less common with beta-lactam antibiotics compared to antiepileptic drugs. Beta-lactam antibiotics are a class of antibiotics that primarily treat infections caused by Gram-positive bacteria.

**Clinical Pearl:** Fixed drug eruptions are a rare but potentially serious adverse drug reaction. It is essential for healthcare professionals to be aware of these reactions and document any previous reactions to avoid re-exposure to the causative drug. In patients presenting with a new skin lesion, it is crucial to inquire about any previous drug exposure that may have led to a similar reaction.

**Correct Answer:** Antiepileptic drugs (D) are associated with a higher frequency of fixed drug eruptions, due to increased sensitization caused by hapten formation. This process is more common with drugs that have a molecular weight greater than 500 Da (Drug Hapten Theory).

**Explanation:** Fixed drug eruptions are an immune response to a hapten, a small molecule that binds covalently to proteins in the skin. The immune system recognizes these haptenated proteins as foreign and mounts an immune response, leading to sensitization and subsequent reactions upon re-exposure to the drug.

This process is more common with drugs that have a molecular weight greater than 500 Da (Drug Hapten Theory). Antiepileptic drugs, such as carbamazepine, phenytoin, and phenobarbital, have a higher molecular weight than most other drugs, making them more likely to cause sensitization and subsequent fixed drug eru