Penicillin and abacavir are most associated with which idiosyncratic reaction?

• A. Malignant hyperthermia
• B. Allergic reactions/hypersensitivity
• C. Drug-induced liver injury
• D. Toxic epidermal necrolysis (SJS)

Answer: (B)

The main concept here is idiosyncratic, immune-mediated drug reactions—hypersensitivity. Penicillin is a classic trigger of allergic reactions that can range from rash to anaphylaxis, illustrating how the body’s immune system can overreact to a drug. Abacavir is well known for a systemic hypersensitivity syndrome, heavily tied to a specific genetic marker (HLA-B*57:01), which makes this hypersensitivity a hallmark adverse reaction for that drug.

These reactions aren’t about dose or predictable toxicity; they’re immune-driven and can occur unpredictably in susceptible individuals. That’s why allergic reactions/hypersensitivity is the best fit. Malignant hyperthermia is linked to certain anesthetics, not penicillin or abacavir. Drug-induced liver injury can occur with many drugs but is not the primary association here. Toxic epidermal necrolysis is a severe form of hypersensitivity but remains a specific, less common manifestation within the broader allergic/hypersensitivity category.