Non-IgE mediated mast-cell activation to fluoroquinolones (FQ) is prevalent and complicates both clinical and skin-test diagnosis of true IgE mediated reactions.
Consecutive patients(n=101) with immediate or accelerated reactions to FQ underwent prick (SPT)/intradermal skin (IDT) (0.005;0.025 mg/ml) testing to ciprofloxacin, levofloxacin, and moxifloxacin followed by single dose 250 mg oral challenge(OC) to the implicated FQ.
3/101 (2.97%) patients had immediate histories consistent with moxifloxacin anaphylaxis. 101/101(100%) were SPT negative. 2/3 patients with anaphylaxis were moxifloxacin IDT positive but negative to ciprofloxacin and levofloxacin at 0.005 mg/ml. Of 98/101 who were IDT 0.005 mg/ml negative to all FQ, 56/56(100%) of patients who underwent single dose OC to >1 FQ were tolerant, and 19/56 (34%) subsequently tolerated a therapeutic course of >1 FQ (5-41 days; median duration 12 days). Using OC as the gold standard, the performance of 0.005 mg/ml IDT FQ was: negative predictive (NPV) 98.25%(95%CI 91.9-99.6); positive predictive value (PPV) 100%; sensitivity (66.7%); specificity (100%). IDT 0.025 mg/ml was equally sensitive, however was positive in 7 patients who tolerated OC (PPV 22.2%[95%CI 9-45.2%; specificity 87.5%]. 76/101 (75%) of those FQ tested had been labeled as penicillin allergic prior to FQ exposure of which 100% were subsequently negative on penicillin SPT/IDT/OC, suggesting that FQ use is in part driven by history of penicillin allergy.
Negative IDT testing to FQ at 0.005 mg/ml followed by low dose FQ (250 mg) OC may be a useful testing strategy in allergy practice to define patients without true IgE-mediated reactions likely to be FQ tolerant.