Severe anaphylactoid reaction to nalidixic acid.

We present the case of a 58-year-old non-atopic woman who suffered an adverse reaction to orally administered nalidixic acid, which had been prescribed for the treatment of a urinary tract infection. The single-blind oral provocation test was positive; the patient presented the clinical features of an anaphylactoid reaction 3 min after administration of nalidixic acid. Both the skin test and the histamine release test were negative. These results suggest that we are dealing with an anaphylactoid reaction not described before with this drug.