Approximate loss of penicillin skin-test positivity with time

• 1 year – 10-20%
• 5 years – 40%
• 10 or more years -80%

(10% loss of sensitivity per year to 10 years)

Patients with a documented acute penicillin reaction caused by IgE antibodies (immediate reaction) have a decline in those antibodies and can disappear with time resulting in most patients becoming skin-test negative after 10 years. Individuals who have lost skin-test reactivity to penicillins are at negligible risk of becoming resensitized when exposed to penicillin or other beta-lactam antibiotics in the future.

Results from an early study looking at the change in skin-test positivity over time showed that the prevalence of positive skin-test reactions changed dramatically with increasing time after the last known exposure to beta-lactam antibiotics. (2)

Twenty two percent of the subjects tested 10 years or more after a reaction were skin-test positive, i.e., almost 80% of subjects lost their skin-test positivity and, therefore, could be treated with a beta-lactam antibiotic.

Another study evaluating the evolution of skin-test sensitivity with time in patients allergic to beta-lactam antibiotics showed the following loss of skin-test positivity (13)

• 1 year – 20%
• 3 years – 28%
• 5 years – 33%