Neomycin sensitivity can be detected in more than 90% of all cases with a 48-hour occlusive patch test of 20% aqueous neomycin sulfate. Delayed reactions are common, and five to seven day readings must be made if the test is negative at the initial observation.
An occasional case of neomycin sensitivity will have negative patch tests even to the 20% neomycin concentration. In such an instance, intradermal testing is indicated. With proper technique, intradermal testing for neomycin sensitivity is reliable.
Preliminary excoriation of a neomycin patch test site (scratch-patch test) results in frequent primary irritant reactions which at times are difficult to distinguish from an allergic reaction. The scratch-patch test is too erratic for clinical practice.
The clinical manifestations of neomycin allergy are frequently subtle and atypical. To avoid overlooking such cases of neomycin sensitivity, a high index of suspicion must be combined with proper patch testing.
EPSTEIN E. Detection of Neomycin SensitivityA Comparison of Testing Techniques. Arch Dermatol. 1965;91(1):50–53. doi:10.1001/archderm.1965.01600070056006