Thank you for your recent inquiry.
You are correct in that the literature is rather sparse in terms of reports of desensitization to metronidazole. However, I was able to find three additional articles dealing with this issue. Although I have not read them personally, the experiences cited in these articles should be helpful to you in designing a desensitization protocol for metronidazole should you decide to do so.
Thank you again for your inquiry and we hope this response is helpful to you.
Allergol Immunopathol (Madr). 2006 Mar-Apr;34(2):70-2.
Hypersensitivity reactions to metronidazole.
García-Rubio I, Martínez-Cócera C, Santos Magadán S, Rodríguez-Jiménez B, Vázquez-Cortés S.
Allergy Department, Hospital Clínico San Carlos, Madrid Spain. email@example.com
BACKGROUND: Hypersensitivity reactions to metronidazole are infrequently described. However, we believe that such reactions are increasing due to growing use of the drug for the treatment of amebiasis and anaerobe infections combined with other antibiotics. The present study assesses the need for oral provocation in patients with probable hypersensitivity reactions to metronidazole.
METHODS: We performed cutaneous prick tests with spiramycin and metronidazole as well as epicutaneous tests with metronidazole at different concentrations in four patients with cutaneous reactions to Rhodogil (metronidazole plus spiramicyn). Controlled oral challenges were then carried out with placebo using erythromycin, spiramycin and metronidazole except in the last patient due to a positive prick test.
RESULTS: Only one patient showed a positive metronidazole prick test. The epicutaneous tests were negative. All patients tolerated erythromycin and spiramycin up to therapeutic doses. Oral provocation with metronidazole proved positive, the first patient presenting a delayed exanthema and the other two early erythema and itching.
CONCLUSIONS: We present four cases of cutaneous exanthemas caused by metronidazole (two early and two delayed) and probably mediated by an immune mechanism which we have only been able to demonstrate in one case. Taking into account the low sensitivity of the cutaneous tests (prick tests and epicutaneous tests), oral provocation must be considered the "gold standard" for establishing the diagnosis in many cases of hypersensitivity reactions to metronidazole.
Am J Obstet Gynecol. 2008 Apr;198(4):370.e1-7. Epub 2008 Jan 25.
Management of trichomonas vaginalis in women with suspected metronidazole hypersensitivity.
Helms DJ, Mosure DJ, Secor WE, Workowski KA.
Division of STD Prevention, Coordinating Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA. firstname.lastname@example.org
BACKGROUND/OBJECTIVE: Standard treatment for Trichomonas vaginalis is metronidazole or tinidazole. Hypersensitivity to these drugs has been documented but is poorly understood. Desensitization is an option described in limited reports of women with hypersensitivity to nitroimidazoles. The purpose of this analysis is to improve documentation of management for trichomonas infections among women with metronidazole hypersensitivity.
STUDY DESIGN: Clinicians who consulted Centers for Disease Control and Prevention concerning patients with suspected hypersensitivity to metronidazole were provided with treatment options and asked to report outcomes.
RESULTS: From September 2003-September 2006, complete information was obtained for 59 women. The most common reactions were urticaria (47%) and facial edema (11%). Fifteen of these women (25.4%) were treated with metronidazole desensitization and all had eradication of their infection. Seventeen women (28.8%) were treated with alternative intravaginal drugs, which were less successful; 5 of 17 infections (29.4%) were eradicated.
CONCLUSION: Metronidazole desensitization was effective in the management of women with nitroimidazole hypersensitivity
(AM J OBSTET GYNECOL1996;174:934-6.)
OBJECTIVE: Our purpose was to develop and test an incremental dosing protocol for women with adverse reaction to metronidazole and severe symptomaticTrichomonas vaginitis. STUDY DESIGN: Two women with documented Trichomonas infection and presumed metronidazole allergy were initially treated with a number of alternative methods without success. With persistent severe symptoms associated with their infection, these women were admitted to the hospital and underwent an intravenous incremental metronidazole dosing protocol. RESULTS: Both patients were successfully treated without adverse event. They are both symptom-free and apparently cured several months after treatment. CONCLUSION: This protocol offers a new therapeutic option to women with adverse metronidazole reactions and severe symptomatic Trichomonas vaginitis resistant to treatment with nonmetronidazole therapy.
Phil Lieberman, M.D.
Key Words: metronidazole, drug allergy, desensitization, urticaria, angioedema