Treating the Penicillin-allergic Patient

A frequent challenge when prescribing antibiotics is what to prescribe for the patient who states they are allergic to penicillin. This is particularly true when prescribing cephalosporins. The frequently quoted rate of cross-sensitivity between penicillin and cephalosporins is between 5 and 10%.

However, recent studies show that the rate is actually less than 1%. When prescribing cephalosporins for penicillin-allergic patients, clinicians should realize that any possible reaction is not due to a β-lactam ring but due to the R group side chain. Drugs of similar side chains to penicillin include cefotaxime, cefaclor, ceftriaxone, cefpodoxime, cefepime, and cephaloridine.

When assessing for cross‐reactions it is important to know what type of reaction the patient had to penicillin. The only significant reaction to note is a type I anaphylaxis reaction. In patients with documented anaphylaxis to penicillin avoid use of cephalosporins with similar R group side chains.

Both second- and third-generation cephalosporins are highly unlikely to demonstrate cross‐reactivity to penicillin based on their structures compared to early-generation cephalosporins.