Pharmacology · Antitrypanosomals
Benznidazole !
The preferred drug for Chagas disease: it cures acute and congenital infection; its most typical adverse effect is dermatitis.
Updated 2026-11-01
Mechanism of action
A nitroimidazole that enters the parasite as a prodrug. The NADH-dependent mitochondrial nitroreductase of T. cruzi reduces its nitro group, producing reactive metabolites that bind the parasite's DNA, lipids and proteins. It kills both blood trypomastigotes and the amastigotes that multiply inside heart and gut cells.
- Enters T. cruzi as a nitroimidazole prodrug
- The parasite nitroreductase reduces its nitro group
- Reactive metabolites damage DNA, lipids and proteins
- Trypomastigotes and amastigotes die
Pharmacokinetics
- Absorption
- Oral; peak blood level in about 2 hours fasting, somewhat later after a high-fat meal
- Distribution
- 44 to 60 % bound to plasma proteins; passes into breast milk
- Metabolism
- Nitro reduction followed by glucuronidation; a P-glycoprotein substrate
- Elimination
- Mostly in urine as metabolites (little unchanged drug), part in faeces
- Half-life
- About 13 hours
Indications
- Acute Chagas disease, including reactivation Chagas disease →
- Congenital T. cruzi infection in the newborn Chagas disease →
- Chronic infection in children and in women of childbearing age (prevents congenital transmission) Chagas disease →
- Adults with chronic Chagas disease without advanced cardiomyopathy, to slow progression Chagas cardiomyopathy →
Adverse effects
Common
- Allergic dermatitis and rash, the most characteristic effect
- Abdominal pain, nausea and vomiting
- Loss of appetite and weight loss
- Headache and insomnia
- Raised transaminases
Contraindications
- Hypersensitivity to benznidazole or other nitroimidazoles
- Disulfiram use in the previous two weeks
- Cockayne syndrome (fatal hepatotoxicity with metronidazole, a relative)
- Pregnancy
- Severe kidney or liver failure
Key interactions
- Disulfiram
- Psychotic reactions have been reported with nitroimidazoles; contraindicated within two weeks of disulfiram
- Alcohol
- Avoided during treatment because of poor gut tolerance; unlike metronidazole, the label does not expect a disulfiram-like reaction
What is monitored
- Complete blood count during treatment
- Skin: rash, fever, blisters or mucosal involvement
- Neurological symptoms: tingling or numbness in hands and feet
- Weight and appetite
- Pregnancy test before starting in women of childbearing age
Administration and safety
- Oral, as a long course (up to two months) with regular check-ups.
- Giving it with food improves gut tolerance.
- Name looks like metronidazole and other nitroimidazoles: confirm the drug and the indication.
Nursing care
- Before: pregnancy test, blood count, kidney and liver function, and ask about recent disulfiram use.
- Check the skin at every visit; rash usually appears in the first weeks and is reported at once if there is fever, blistering or mucosal lesions.
- Ask about tingling, burning or weakness in hands and feet: neuropathy means stopping the drug.
- Track weight and appetite; watch for fever or sore throat (possible neutropenia).
- Teaching: effective contraception during treatment and for a few days after; no breastfeeding during treatment; finish the course.
Pregnancy and breastfeeding
May harm the fetus based on animal studies; chronic Chagas disease is not treated during pregnancy. Treating the woman before or after pregnancy prevents congenital transmission.
Test yourself
Think of the answer, then tap the question to see it.
How does benznidazole work?
It is a nitroimidazole prodrug: T. cruzi nitroreductase reduces it to reactive metabolites that damage the parasite's DNA, lipids and proteins.
What is the most typical adverse effect of benznidazole?
Allergic dermatitis or rash, usually in the first weeks; severe forms (DRESS, necrolysis) mean stopping it.
Which drug is contraindicated in the two weeks before benznidazole?
Disulfiram, because psychotic reactions have been reported with nitroimidazoles.
Does benznidazole reverse established Chagas cardiomyopathy?
No. It can slow progression in the early chronic phase but does not reverse established heart damage.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - BENZNIDAZOLE tablet (DailyMed (U.S. National Library of Medicine), 2026); Chagas disease (also known as American trypanosomiasis) (World Health Organization, 2025); Clinical Care of Chagas Disease (Centers for Disease Control and Prevention (CDC), 2024); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 67 (McGraw Hill, 2023).
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