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.