Modified Oral Metronidazole Desensitization Protocol

Abstract

The Center for Disease Control guidelines recommend desensitization to metronidazole in patients with trichomoniasis and hypersensitivity to metronidazole. There is only one published oral metronidazole desensitization protocol. The purpose of this study was to design a new, more gradual oral desensitization protocol to decrease systemic reactions that may occur when using the previously published protocol. We present two patients with presumed IgE-mediated allergy to metronidazole who underwent oral desensitization using our modified protocol. Case 1 was a 65-year-old woman with trichomoniasis who presented for metronidazole desensitization with a history of intraoperative anaphylaxis and positive skin tests to metronidazole. The patient tolerated six doses of the modified desensitization but developed systemic symptoms of nasal congestion and diffuse pruritus after the 25- and 100-mg doses. Both reactions were treated with intravenous (i.v.) antihistamines. Because of gastrointestinal irritation, the desensitization was completed at a dose of 250 mg orally every 6 hours. Case 2 was a 42-year-old woman with trichomoniasis and a history of hives immediately after administration of i.v. metronidazole who presented for desensitization. The patient had negative skin-prick and intradermal testing to metronidazole. She developed lip tingling and pruritus on her arms 15 minutes after the 10-mg dose. Fexofenadine at 180 mg was given orally and symptoms resolved. She tolerated the rest of the protocol without reaction and received a total dose of 2 g of metronidazole. Our oral metronidazole desensitization for presumed IgE-mediated reactions offers a second option for physicians wishing to use a more gradual escalation in dose.

Sexually Transmitted Infections Treatment Guidelines, 2021

“…Metronidazole and tinidazole are both nitroimidazoles. Patients with an IgE-mediated-type hypersensitivity reaction to 5-nitroimidazole antimicrobials should be managed by metronidazole desensitization according to published regimens ( 1127 , 1128 ) and in consultation with an allergy specialist. The optimal treatment for patients with T. vaginalis who are unable to be desensitized has not been systematically investigated and is based on case reports, some of which report using paromomycin or boric acid for treating T. vaginalis ( 1123 , 1129 ).…”

Recent advances in the epidemiology, diagnosis, and management of Trichomonas vaginalis infection

“…Another complicated treatment scenario for women with trichomoniasis is the setting of an IgE-mediated-type hypersensitivity reaction to 5-nitroimidazoles. These patients should be managed by MTZ desensitization according to a published regimen 72, 73 and in consultation with an allergy specialist 21 . Treatment of patients with T. vaginalis who are unable to be desensitized is difficult and mainly based on anecdotal data 21, 74 .…”

Antimicrobial Desensitization: A Review of Published Protocols

“…In patients at high risk of immediate HSR to metronidazole without alternatives, such as in the case of Trichomonas vaginalis , desensitization should be performed [22]. Multiple case series have been published confirming the efficacy of both IV (Supplementary Materials Table S10 in the Supplementary) and oral (Supplementary Materials Table S11 in the Supplementary) desensitization protocols [128,129,130].…”