Tobramycin-neomycin cross-sensitivity

Fifty normal control volunteers were patch tested to 20% neomycin as well as tobramycin 1%, 10%, 20% and 30% in white petrolatum. Tobramycin is a new aminoglycoside antibiotic for prescription ophthalmologic use in the United States. There were no reactions on any of the control volunteers. Twenty known and proven neomycin-allergic patients were then tested to tobramycin 10% and 20% in white petrolatum, as well as to neomycin 20% aqueous and 20% in white petrolatum. All 20 reacted with a 2+ or greater response to the neomycin patch tests. Twelve out of the 20 or 60% of the neomycin-allergic patients reacted to the 10% tobramycin in white petrolatum. Thirteen out of 20 or 65% reacted to 20% tobramycin in white petrolatum. From these data, tobramycin (ophthalmic) should not be used to treat known neomycin-allergic patients without first patch testing the patient with 20% tobramycin in white petrolatum. It appears probable that 65% of neomycin-allergic patients would react with a dermatitic response to such therapy.