**Question:** Patient has been given pencilling 48hrs ago, with no history of drug allergy. Now he develops wheeze, hemolysis, and an antibody for pencilline is positive. Type of hypersensitivity is which of the following:

A. Drug-induced anaphylaxis
B. Drug-induced hypersensitivity reaction
C. Drug-induced eosinophilia and myalgia syndrome
D. Drug-induced thrombocytopenia

**Core Concept:**

The correct understanding of drug hypersensitivity reactions is essential for diagnosing and treating these adverse drug reactions. Drug hypersensitivity reactions can be classified into four types based on the immune response:

1. Type I: Immediate hypersensitivity reactions (also known as immediate reactions or anaphylaxis).
2. Type II: Drug-induced hemolysis (antibody-mediated reactions).
3. Type III: Drug-induced immune complex-mediated reactions (e.g., Drug-induced eosinophilia and myalgia syndrome).
4. Type IV: Delayed hypersensitivity reactions (e.g., Drug-induced thrombocytopenia).

**Why the Correct Answer is Right:**

The patient receiving pencillin (penicillin) develops hemolysis, wheeze, and a positive pencillin antibody test. This indicates a Type II hypersensitivity reaction, specifically, drug-induced hemolysis.

**Why Each Wrong Option is Incorrect:**

A. Drug-induced anaphylaxis (Type I) is characterized by an immediate reaction (e.g., urticaria, hypotension, and respiratory distress) but not hemolysis.

B. Drug-induced hypersensitivity reactions (Type IV) involve delayed immune responses (e.g., Drug-induced thrombocytopenia), not hemolysis and wheeze.

C. Drug-induced eosinophilia and myalgia syndrome is a Type III reaction characterized by eosinophilia, myalgia, and elevated liver enzymes, but not hemolysis, wheeze, and positive pencillin antibody test.

D. Drug-induced thrombocytopenia is a Type IV hypersensitivity reaction characterized by thrombocytopenia (low platelet count), not hemolysis, wheeze, and a positive pencillin antibody test.

**Clinical Pearl:**

In cases of drug-induced hemolysis, the presence of hemolysis, wheeze, positive pencillin antibody test, and no history of anaphylaxis make this a Type II hypersensitivity reaction. This is a delayed response involving the complement system and immune complex formation with subsequent release of histamine and other mediators leading to clinical manifestations like hemolysis and wheeze. The positive pencillin antibody test confirms the immune-mediated mechanism.

In summary, the correct answer is Type II hypersensitivity reaction (D), specifically drug-induced hemolysis.