Mohamed-Kalib et al. illustrate 2 important caveats to penicillin skin testing (PST): (1) there is an exceptionally rare potential for resensitization, a phenomenon in which a previously reactive patient is proven tolerant, then develops sensitivity and has a positive PST; (2) consider repeating PST prior to a parenteral β-lactam prescription in patients who previously reported severe anaphylactic reactions.

Our negative predictive value of 100% does not abate the tentative concern for resensitization.[1] Similar to the likelihood of becoming allergic initially, 0% to 3.2% of PST-negative patients can become allergic again, more commonly with parenteral therapy and among children.[2-4]

The author describes a seemingly resensitized patient who reacted in an outpatient setting. Theoretically, anyone could resensitize, regardless of their setting or whether a single dose or full course was given after the PST. Individuals with a proven tolerance by PST and repeated courses are at a very low risk of future immunoglobulin E-mediated reactions, a risk similar to that of the general population.

Whether previously reactive or not, patients receiving medicinal therapies should always be monitored for allergic reactions. Although PST may not be prudent in the minority of patients who report recent or severe reactions, a repeat PST prior to prescribing parenteral β-lactam may potentially avoid instances described by Mohamed-Kalib et al.

  • Ramzy H. Rimawi, MD1

  • 1Department of Internal Medicine–Division of Critical Care Medicine

  • The Brody School of Medicine at East Carolina University

  • Greenville, North Carolina


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