NZ Formulary

Isoniazid and rifampicin

eye-so-nye-ah-zid and rif-am-pee-sin

What does it do?

Isoniazid and rifampicin is used to treat tuberculosis.

How should you take it?

Take isoniazid and rifampicin regularly as directed with a glass of water.
Take each dose on an empty stomach - one hour before or two hours after food.
Keep taking isoniazid and rifampicin until the course is finished, even if you start to feel better.

What if you forget a dose?

Take the missed dose as soon as possible. If it is close to the time for your next dose, skip the missed dose and carry on as normal. Do not take two doses at the same time.
If you often forget to take isoniazid and rifampicin, your tuberculosis may not be fully treated.

Can you take other medicines?

Some medicines available without a prescription may react with isoniazid and rifampicin including:

  • antacids (e.g. Mylanta®) - do not take these within two hours of taking isoniazid and rifampicin.

Rifampicin can alter the effects of many medicines, sometimes with severe results.

Tell your pharmacist or doctor about all medicines or treatments that you may be taking including vitamins, herbal products (e.g. St John’s wort) or recreational drugs.

Important information continues on next page.

What side effects might you notice?

Side EffectsRecommended action

Symptoms of liver problems including: yellow skin or eyes, itching, dark urine, pale bowel motions, abdominal pain

Reduced number of blood cells that help your blood to clot - symptoms include: easy or unusual bruising or bleeding

Numbness or tingling of the fingers or toes

Dizziness, slurred speech, unsteadiness

Tell your doctor immediately

Skin rash

Tell your doctor

Nausea, stomach upset


Muscle weakness or pain

Flu-like symptoms (fever, chills, bone aches)

Tell your doctor if troublesome

Red/orange body fluids

Do not wear soft contact lenses (they may be permanently stained)

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • Tell your doctor if you have liver or kidney problems, or epilepsy.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • Limit alcohol intake while taking isoniazid and rifampicin. Alcohol may increase the risk of liver problems.
  • If you are taking an oral contraceptive you will need to use additional birth control methods while taking isoniazid and rifampicin, and for four weeks after stopping.
  • Your doctor may prescribe pyridoxine (vitamin B6) to prevent tingling of the fingers or toes, which can sometimes be a side effect of isoniazid.
  • Do not stop taking isoniazid and rifampicin without talking to your doctor first.