Metronidazole hypersensitivity and oral desensitization

Abstract

The patient was a 31-year-old black woman first diagnosed with vaginal Trichomonas 4 to 5 years ago. Approximately 10 minutes after taking a single dose of metronidazole (2 gm orally), she developed hives over her entire body, followed by shortness of breath. Her symptoms resolved spontaneously after 15 minutes. Two years ago, the patient again developed vaginal Trichomonas and was treated with metronidazole, followed by the same symptoms. The patient was treated in the emergency room with subcutaneous epinephrine. During the past year, the patient has had a persistent Trichomonas infection despite multiple clinic visits and alternative treatments to metronidazole, including topical clotrimazole cream and zinc oxide. The patient had no other drug or food allergies. Physical examination was significant only for vaginitis with a strawberry type cervix and yellow frothy discharge. Laboratory data were positive by wet-drop examination and Trichomonas direct fluorescent Ab test. The patient was referred for an allergy consultation for metronidazole desensitization for persistent Trichomonas (Table I). At approximately one half the therapeutic dose (750 mg), the patient developed an urticarial lesion associated with throat tightness within 10 minutes. Blood pressure remained stable, and her chest was clear to percussion and auscultation. Treatment with an antihistamine (astemizole, 10 mg orally, one dose) and corticosteroids (dexamethasone, 8 mg intramuscularly, one dose) was then administered. The urticarial lesion and chest tightness re-