Allergy to Benznidazole: Cross-Reactivity with Other Nitroimidazoles
Saturday, March 5, 2016
South Exhibit Hall H (Convention Center)
Blanca Noguerado, MD, Patricia Rojas, MD, Maria Calderon, MD, Cristina Morales, MD, Pilar Tornero, MD

Benznidazole (Bzn) is a nitroimidazole drug used as first-line treatment for Chagas disease, a potentially life-threatening illness caused by Trypanosoma cruzi. Many adverse effects had been reported with it, including allergy reactions such as exanthemas, dermatitis and AGEP.

Alternative therapeutic nitroimidazole drugs for this group of patients are important for treatment of other parasitic infections.

We aim to study hypersensitivity reactions to Bzn and cross-reactivity with metronidazole (Mtn), another nitroimidazole drug. 


Five patients with non-immediate skin reactions due to Bzn, all presented with maculo-papular exanthema, were referred to our Allergy Department.

Patch tests (PT) with Bzn 10% and Mtn 10% in DMSO, were made with readings at day 2 (D2) and D4.

Single blind oral challenge test (SBOCT) was performed in patients with allergy confirmed to Bzn and negative PT with Mtn.


PT with Bzn were positive in 5/5 patients (100%) at D2 and D4.

PT with Mtn were negative in 4/5. Only one patient had both positive PT.

SBOCT with Mtn was negative in all of them (4/4).  


PT with Bzn was diagnostic in 100% of patients so was very useful for the diagnosis, suggesting type IV-hypersensitivity mechanism.

Cross-reactivity between Bzn and Mtn was low, only found in 1 patient that was sensitizated to both nitroimidazoles.

100% of patients with negative PT to Mtn had negative SBOCT (negative predictive value of 100%).

We think that is important to test both drugs in these patients in order to give them alternative therapeutic treatment for other parasitosis disease.