Simultaneous positive patch test reactions to neomycin and low-molecular-weight heparins: possible cross-reaction?

Background A patient received enoxaparin sodium subcutaneous injections for prophylaxis after surgery and developed inflammatory skin reactions on injection sites on Day 5 after the first administration. Patch test was performed with baseline series and low-molecular-weight heparins (LMWHs) at different concentrations and showed positive reactions to neomycin and LMWHs. Cross-reactivity between neomycin and LMWHs was suspected due to similar structure. Objectives To establish the evidence of possible cross reaction between neomycin and LMWHs by patch testing. Materials & Methods Patch testing of 12 individual controls with a history of neomycin contact allergy was performed. Results Positive patch test reactions to enoxaparin sodium, tinzaparin sodium, and neomycin sulphate were reported in the patients. None of the controls reacted to LMWHs. Conclusion There was no proof of cross reaction between neomycin and LMWHs in this study, suggesting that the simultaneous reaction may be a coincidence. Since the number of individuals studied was low, allergy to LMWHs following injection in individuals with a history of neomycin allergy should be further investigated.