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Generic name: guanidine [ GWAN-ih-deen ]
Brand name: Guanidine HCl
Dosage form: oral tablet (125 mg)
Drug class: Cholinergic muscle stimulants

What is guanidine?

Guanidine is used to treat muscle weakness caused by Eaton-Lambert syndrome. Guanidine will not treat myasthenia gravis.

Guanidine may also be used for purposes not listed in this medication guide.


Guanidine can increase your risk of bleeding or infection. Call your doctor if you have unusual bruising or bleeding, or new signs of infection (fever, chills, tiredness, mouth sores).

Before taking this medicine

You should not use guanidine if you are allergic to it.

Tell your doctor if you have ever had a weak immune system (caused by disease or by using certain medicine).

It is not known whether guanidine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

You should not breast-feed while using this medicine.

Guanidine is not approved for use by anyone younger than 18 years old.

How should I take guanidine?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Guanidine doses are based on weight. Your dose needs may change if you gain or lose weight.

Guanidine can increase your risk of bleeding or infection. You will need frequent medical tests.

Your kidney function may also need to be checked.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include diarrhea, vomiting, tremors, and severe muscle spasms or twitching.

What should I avoid while taking guanidine?

Avoid being near people who are sick or have infections. Tell your doctor at once if you develop signs of infection.

Guanidine side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Guanidine may cause serious side effects. Call your doctor at once if you have:

  • severe or ongoing stomach problems;

  • a light-headed feeling, like you might pass out;

  • painful urination, blood or pus in your urine;

  • fast or pounding heartbeats;

  • confusion, hallucinations, unusual thoughts or behavior;

  • problems with balance or muscle movement;

  • tremors; or

  • low blood cell counts--fever, chills, tiredness, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet, feeling light-headed or short of breath.

Common side effects of guanidine may include:

  • nausea, diarrhea, stomach cramps;

  • numbness or tingling (especially in your face, hands, or feet);

  • feeling nervous or irritable;

  • abnormal liver function tests;

  • flushing (sudden warmth, redness, or tingly feeling);

  • dry mouth, upset stomach, loss of appetite;

  • sweating, rash, dry or scaly skin; or

  • redness or crusting around your hair follicles.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect guanidine?

Tell your doctor about all your other medicines, especially drugs that weaken the immune system such as cancer medicine, steroids, and medicines to prevent organ transplant rejection.

Other drugs may affect guanidine, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.