Drug allergy testing and oral challenge test protocol with metronidazole

RATIONALE: Metronidazole is the representative of nitroimidazoles the only class of medicines that is used for treatment of Trichomonas vaginalis and also a drug of choice in other infections: amebiasis; giardiasis; anaerobic bacterial and treponemal infections. Types I, II, and IV hypersensitivity reactions to metronidazole have been reported in the literature. Development of comprehensive protocol with validation of non-irritant concentrations for skin testing and intradermal testing was an unmet need that we addressed in our centre.

METHODS: We developed protocol for drug allergy testing that includes Basophil activation test (Reflab, Denmark), patch testing (AllergEase MS380 metronidazole, 1%, pet), skin prick testing in 1:100, 1:10 and maximum non-irritant concentration for skin testing 5 mg/mL, intradermal testing 1:1000; 1:100, 1:10 of maximum non-irritant concentration 2.5 mg/mL and oral allergen challenge test up to cumulative dose of 800mg given at 30 min intervals and observation of 2 hours for negative test or in case of positive result observation and treatment was determined clinically with an option of use of desensitisation protocol if required.

RESULTS: This protocol allows to reduce risks of severe reactions during testing starts with laboratory tests and patch tests that help to give information on both delayed and immediate response. This protocol is designed for use in ambulatory care as a day case admission in the hospital setting with all required emergency care available on standby.

CONCLUSIONS: This method is validated and is used routinely in clinical practice. London Allergy and Immunology Centre is a member of the European Network for Drug Allergy ENDA