Some patients (1-10%) may have cross-reactivity with ________, which are often avoided in penicillin-allergic patients.

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

Answer: (C)

Cross-reactivity among beta-lactam antibiotics is what this question targets. Penicillins and cephalosporins both contain a beta-lactam ring, so in some patients who are allergic to penicillin, the immune system may recognize a cephalosporin similarly and trigger a reaction. That historical concern is why cephalosporins are often avoided in penicillin-allergic patients, with estimates of cross-reactivity ranging around a small percentage. In practice, the risk is relatively low, especially with later-generation cephalosporins and when the penicillin allergy isn’t a severe immediate reaction. Macrolides and sulfonamides are not beta-lactams and do not share the same cross-reactivity mechanism, so they are not typically avoided for that reason.