Which drug is most commonly associated with serum sickness?

The drug most commonly associated with serum sickness is actually penicillin. Serum sickness is a type III hypersensitivity reaction often linked to medications that are recognized as foreign by the immune system, leading to the production of antibodies and subsequent inflammation.

Penicillin and its derivatives are well-documented triggers of serum sickness due to their immunogenic properties when broken down by the body. They can elicit an immune response that results in the symptoms characteristic of serum sickness, such as fever, rash, arthralgia, and sometimes more severe manifestations.

While sheep Fab anti-venom for snake bites can induce serum sickness as a non-human protein, it is not as commonly associated with this condition as penicillin. Other medications listed, such as ciprofloxacin and ibuprofen, are less frequently implicated. Ciprofloxacin is a fluoroquinolone antibiotic and generally not associated with serum sickness. Ibuprofen, a non-steroidal anti-inflammatory drug (NSAID), does not typically invoke a serum sickness reaction as it primarily works by inhibiting cyclooxygenase enzymes and does not have the immunogenic characteristics of penicillin.

Thus, penicillin's association with serum sickness is due to its ability to provoke a strong immune response compared to the other options presented.