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Generic Name: Isoniazid [Eye-so-NYE a-zid]
Brand name: Nydrazid
Dosage Forms: Oral Syrup (50 mg/5 mL), orally disintegrating tablet (100 mg, 300 mg).
Drug class: hydrazide derivatives

What is Isoniazid?

Isoniazid is an antibacterial. It is used both to treat and prevent TB. It is possible that you will need to take another TB medicine in conjunction with isoniazid.

Isoniazid should be taken with other TB medications when treating active TB. If isoniazid alone is used, TB can become resistant to the treatment. Follow your doctor's prescription for all medications. This medication guide does not list all possible uses of isoniazid.

Side effects of Isoniazid

If you experience symptoms of an allergic reaction, such as hives, difficulty breathing, swelling on your face or in your throat, or a severe reaction to your skin (such as a fever, sore throat, burning in the eyes, or skin pain or rashes that are red or purple and cause blistering or peeling), seek emergency medical attention.

Seek medical attention if you experience a serious reaction to a drug that affects many parts of the body. The symptoms may include: skin irritation, fever, swollen lymph glands, flu-like symptoms, muscle pain, severe weakness, or unusual bruising. This reaction can occur weeks after starting isoniazid.

Isoniazid may cause serious side effects. If you experience:

  • If you feel ill or weak or have a fever lasting 3 days or more,
  • Nausea and pain in the upper abdomen (which may spread to your back) are symptoms of this condition.
  • Dark urine, clay-coloured stool, jaundice
  • Vision changes, pain behind the eyes
  • Memory problems or unusual thoughts and behaviors can cause confusion.
  • a seizure (convulsions);
  • Pale skin, easy bruising, and bleeding (nosebleeds or bleeding gums)

Side effects of isoniazid include:

  • You may experience numbness or burning in your feet or hands.
  • nausea, vomiting, upset stomach,
  • Abnormal liver function tests

There may be other side effects. For medical advice on side effects, call your doctor. The FDA can be contacted at 1-800-FDA-1088 to report side effects.

Similar/related drugs

Ciprofloxacin, levofloxacin, Levaquin, Moxifloxacin, Rifampin, Pyrazinamide, and Rifabutin


If you are suffering from active liver disease or have previously taken isoniazid and experienced liver problems, flu-like symptoms, joint pain, or an allergic reaction, you should avoid using isoniazid.

You may experience serious and even fatal liver problems during or after treatment with this medication, especially if your age is between 35 and 65. You may need to have your liver function checked each month while taking this medication.

If you experience: nausea or upper stomach pain; loss of appetite; and fatigue, call your doctor immediately. Avoid alcohol. Alcohol can increase the risk of liver damage when you take isoniazid.

Before you take this drug

If you are allergic or have any of the following:

  • Active liver disease
  • A history of severe allergy to isoniazid
  • Isoniazid-induced liver damage or hepatitis;
  • A history of severe side effects from isoniazid, such as chills, fever, swelling, and pain in the joints.

Tell your doctor about any of the following to ensure that isoniazid will be safe for you:

  • A history of liver disease
  • Kidney disease
  • Nerve problems that cause pain or weakness;
  • diabetes;
  • HIV or AIDS
  • If you drink alcohol daily,
  • If you are malnourished,
  • If you inject any drugs,
  • If you've ever had to stop using isoniazid,

Before you begin treatment, your doctor will test your liver enzymes to ensure that you can use isoniazid safely. Even months after stopping the medication, serious and even fatal liver problems can occur. Adults between 35 and 65 years of age are at the highest risk of developing liver problems.

Women, particularly those who have Hispanic, African-American, or Hispanic ancestry, are more susceptible to serious liver problems, especially following childbirth. Your doctor can tell you if your risk is higher or lower.

This medicine is not known to harm an unborn child. Notify your doctor immediately if you are pregnant, planning to become pregnant, or trying for pregnancy. If you plan to breastfeed a child during treatment with isoniazid, tell your doctor. This medication can pass through breast milk but will not prevent or treat tuberculosis in the nursing infant.

How to take Isoniazid?

Do not take isoniazid in larger or smaller amounts or for longer than prescribed; always follow your physician's orders when taking isoniazid and do not exceed the recommended dosage or duration. Take isoniazid with an empty stomach at least one hour before or two hours after eating.

You should take this medication for the entire prescribed time. You may experience improvement in your symptoms before the virus has been completely eradicated. You may also be at risk for a second infection resistant to antibiotics if you skip doses. Isoniazid does not treat viral infections such as the flu and common cold.

You may need to have your liver function checked at least once a month while taking this medication.

You may be prescribed extra vitamin B6 by your doctor if you are taking isoniazid. Only take the prescribed amount of vitamin B6. Store away from heat, moisture, and light. Keep the bottle securely closed when not in use.

What happens if I miss the dose?

As soon as you become aware that you missed a dose, take it. If your next scheduled dosage is approaching quickly, disregard any missed ones and move onto taking only what's scheduled. You should not take more medicine to compensate for a missed dose.

What happens if I overdose?

Call 1-800-222-1222 for poison help or seek immediate medical attention.

Overdose symptoms include nausea, vomiting, dizziness, drowsiness, or blurred vision. They may also include hallucinations or trouble breathing.

What should be avoided?

Avoid alcohol. Alcohol can increase the risk of liver damage when you take isoniazid. Certain foods may be avoided while taking isoniazid. You should avoid red wine, aged cheddar, dried meats, and tuna.

Interaction with other drug

Isoniazid can interact with many drugs. These include prescription and over-the-counter medicines, vitamins, and herbal products. This medication guide does not list all potential interactions. Inform your doctor of all medications you take, including those you stop or start using during treatment with isoniazid. Provide a list to all healthcare providers who treat you.