Carbapenems have cross-reactivity with which drugs?

• A. Cephalosporins
• B. Macrolides
• C. Penicillins
• D. Tetracyclines

Answer: (C)

Cross-reactivity arises from shared beta-lactam structure among certain antibiotics. Carbapenems and penicillins both contain the beta-lactam ring, so the immune system can recognize similar features in both drugs. This makes penicillins the class most likely to cross-react with carbapenems. Macrolides and tetracyclines are unrelated in structure and mechanism, so they don’t exhibit this cross-reactivity. Cephalosporins are also beta-lactams, but the clinically relevant cross-reactivity with penicillins is much less, so penicillins are the best-supported match for carbapenems.