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Overview: Benznidazole is used to treat a parasitic infection called Chagas disease. It kills certain parasites by blocking their ability to create proteins and other substances that they need to grow and reproduce. Common side effects include stomach upset, skin reactions, and changes in blood cell counts. Call your health care provider right away if you get a fever, shortness of breath, swollen lymph nodes, headache, rash, or pus-filled pimples.

Uses

What is benznidazole used for?

Benznidazole is commonly used to treat a parasitic infection called Chagas disease.

Benznidazole may not be appropriate for the infection listed above depending on which germs are causing the infection. Parasites in some locations may have developed resistance to benznidazole, which will make it not work as well.

Benznidazole may also be used for other conditions as determined by your health care provider.

How does benznidazole work (mechanism of action)?

Benznidazole kills certain parasites by blocking their ability to create proteins and other substances that they need to grow and reproduce.

How is benznidazole supplied (dosage forms)?

Dosage forms and strengths

  • 12.5 mg, 100 mg oral tablets

How should I store benznidazole?

Benznidazole should be stored at room temperature between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Keep the medicine container tightly closed when you are not using it.

Side Effects

What are the most common side effects of benznidazole?

The most common side effects of benznidazole are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Stomach pain
  • Rash, hives, or itching
  • Weight loss
  • Headache
  • Nausea or vomiting
  • Low levels of neutrophils (neutropenia)
  • High levels of eosinophils (eosinophilia)
  • Loss of appetite

There may be other side effects of benznidazole that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of benznidazole?

While less common, the most serious side effects of benznidazole are described below, along with what to do if they happen.

Severe Allergic Reactions. Benznidazole may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for drug reaction with eosinophilia and systemic symptoms. It is also sometimes called multiorgan hypersensitivity. This is a reaction that can affect multiple parts of the body, including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain
  • Dark colored urine
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Severe Skin Reactions. Benznidazole can cause severe skin reactions, including acute generalized exanthematous pustulosis (AGEP), toxic epidermal necrolysis (TEN) and erythema multiforme (EM), that can lead to death if not treated. If you develop a rash or pus-filled pimples, stop benznidazole and call your health care provider right away. Get emergency help if you have any of the following symptoms of AGEP, TEN, or EM.

  • Rash of pin-sized pustules on top of red skin
  • Painful red or purple skin that looks burned and peels off
  • Flat, red rash or blisters on your skin, mouth, nose, or genitals
  • Red, painful, watery eyes or dry, bloodshot eyes
  • Flu-like symptoms including fever, chills, and muscle aches
  • Red spots, wheals, or blisters on your hands, arms, face, neck, legs, or trunk
  • Joint pain
  • Vision changes
  • Swollen lymph nodes

Nerve Problems. Nerves are the fibers that carry sensations from your body to the brain. Damage to these nerves, called peripheral neuropathy, can happen in people who are taking benznidazole. Stop taking benznidazole and call your health care provider if you develop pain, burning, tingling, numbness, or weakness in your arms, hands, legs, or feet. Benznidazole can also cause problems in your central nervous system. Stop taking benznidazole and contact your health care provider if you develop headache, dizziness, or any other neurological symptoms.

Bone Marrow Suppression. Benznidazole may cause your bone marrow to not make enough cells. This can lead to low blood levels of important cells, such as red blood cells, white blood cells, platelets, and neutrophils. Bone marrow suppression can lead to infections or bleeding. This can be serious or even life-threatening. Keep all appointments to have your blood checked. Tell your health care provider right away if you have any of the following symptoms of bone marrow suppression.

  • Fever
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or bleeding
  • Frequent infection
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Warnings & Precautions

Who should not use benznidazole?

Allergies to Ingredients. People who are allergic to any of the following should not take benznidazole.

  • Benznidazole
  • Any other nitroimidazole derivatives
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in benznidazole.

Drug Interactions. Benznidazole should not be taken while you are using certain other medicines. Before taking benznidazole, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.  See the Interactions section for more details.

Cockayne Syndrome. You should not take benznidazole if you have Cockayne syndrome, which is a rare genetic disorder that affects growth and development.

What should I know about benznidazole before using it?

Do not take benznidazole unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share benznidazole with other people, even if they have the same condition as you. It may harm them.

Keep benznidazole out of the reach of children.

Benznidazole 100 mg tablets can be taken whole or broken at the scored lines to provide the correct dose. Take the exact amount of benznidazole your health care provider tells you to.

For people who cannot swallow tablets, benznidazole tablets can be made into a slurry using water. Follow the instructions given by your health care provider if you will be making the medicine into a slurry.

If you are able to get a partner pregnant, taking benznidazole may decrease your fertility, which can make it more difficult to have a baby. Talk to your health care provider about any fertility concerns you have before taking benznidazole.

What should I tell my health care provider before using benznidazole?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if benznidazole is right for you.

In particular, make sure that you discuss any of the following.

Pregnancy. Benznidazole can harm an unborn baby. If you are able to get pregnant, your health care provider will make sure you are not pregnant before you start taking the medicine. You will need to use effective birth control while taking benznidazole and for five days after your last dose. Tell your health care provider if you are or plan to become pregnant. If you become pregnant while taking benznidazole, call your health care provider right away.

Breastfeeding. Benznidazole passes into breast milk. You should not take benznidazole while breastfeeding. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does benznidazole interact with foods or drinks?

There are no known interactions between benznidazole and foods or drinks.

There are no known interactions between benznidazole and alcohol, but heavy drinking can slow your immune response and make it harder for your body to fight infection.

Does benznidazole interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are taking disulfiram, which is a medicine used to treat alcohol use disorder, or have taken disulfiram within the past two weeks.

This may not be a complete list of medicines that can interact with benznidazole. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much benznidazole?

If you or someone else has used too much benznidazole, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of benznidazole?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.

It is important to complete your prescribed course of benznidazole, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to benznidazole or other similar medicines.