How Should Practitioners Change Their View of Cross-Reactivity Among Beta-Lactams?

Meghan Jeffres, PharmD, assistant professor in the Department of Clinical Pharmacy, University of Colorado Skaggs School of Pharmacy, explains why practitioners need to think about the rate of cross-reactivity between antibiotic penicillin and specific cephalosporins.

Interview Transcript (slightly modified for readability)

“The risk of cross-reactivity between beta-lactams should be [realigned] as the cross-reactivity between specific beta-lactams. Instead of assuming a rate of cross-reactivity between penicillins and cephalosporins, [something] which is classically taught in school, we need to think about the rate of cross-reactivity between the antibiotic penicillin and specific cephalosporins.

One of the more commonly used cephalosporins is cephalexin. This is one of the oral cephalosporins that we use quite a bit in the outpatient setting. It has a similar side chain with amoxycillin and ampicillin, which is also cross-reactive with penicillin. Cefazolin, [however], does not have a similar side chain, and it does not have any cross-reactivity between those two. And so, even though, they are both first generation cephalosporins that are commonly used, they have very different rates of cross-reactivity.

Antibiotics that share a side chain have a cross-reactivity rate of approximately 20%; whereas, dissimilar antibiotics, or ones that do not have any side chain similarities, have a cross-reactivity rate of 0.

[Therefore], we really need to think about this as specific drug-to-drug cross-reactivity versus class cross-reactivity.”