Isoniazid: Uses, How to Take, Dosing & Side Effects

Isoniazid is a prescription antibiotic used to treat and prevent tuberculosis infections. It is often prescribed alone or alongside other medications like rifampin, pyrazinamide, and ethambutol.

This medication is widely available in the United States at local pharmacies in 100 mg and 300 mg tablets. You will need a valid prescription from your healthcare provider to obtain this treatment.

You should only take isoniazid under the direct supervision of an infectious disease specialist or a primary care physician. Completing the full course of treatment is essential to prevent antibiotic resistance and serious health complications.

Woman discussing medication with doctor

What it is for

Isoniazid is primarily used for the following purposes:

  • Preventing tuberculosis (chemoprophylaxis).

  • Treating latent tuberculosis infections.

  • Managing active tuberculosis when used in combination with other antibiotics.

You must follow your doctor’s specific instructions regarding how long to take this medication to ensure the infection is fully cleared.

Also recommended: Tuberculosis Treatment 101: Medications, Care Tips & Recovery tuasaude.com/en/tuberculosis-treatment

How to take

Isoniazid tablets should be taken by mouth with a full glass of water. For optimal absorption, the medication is best taken on an empty stomach, typically 1 hour before or 2 hours after a meal.

The standard dosages for isoniazid based on current clinical guidelines are as follows:

Indication Dosage and administration
Prevention or treatment of latent tuberculosis

Adults: 5 mg/kg of body weight (maximum 300 mg daily) for 6 to 9 months.

Children: 10 mg/kg to 20 mg/kg of body weight (maximum 300 mg daily) for 9 months.

Treatment of active tuberculosis

Adults: 5 mg/kg of body weight daily (maximum 300 mg).

Children: 10 mg/kg to 15 mg/kg of body weight daily (maximum 300 mg).

Must be used in combination with other TB antibiotics.

While a 6 to 9 month course is common, your healthcare provider may extend treatment to 12 months in specific cases. If the medication causes stomach upset, your doctor may advise taking it with a small meal, though this may slightly reduce absorption.

Also recommended: Is Tuberculosis Curable? Treatment Approaches & Guidelines tuasaude.com/en/is-tuberculosis-curable

Possible side effects

The most common side effects associated with isoniazid include nausea, vomiting, stomach pain, or mild allergic reactions.

In some cases, more serious side effects can occur, such as liver inflammation (hepatitis) or nerve damage (peripheral neuropathy). These risks are higher for individuals who are malnourished, consume alcohol regularly, or have pre-existing liver conditions.

Contact your doctor immediately if you experience persistent weakness, extreme fatigue, loss of appetite, dark colored urine, or numbness and tingling in your hands or feet.

Contraindications for use

Isoniazid is not recommended for individuals with active liver disease or a history of severe liver problems.

Additionally, you should not take this medication if you have a known allergy to isoniazid or any of the inactive ingredients found in the tablet.