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What is the most important information I should know about isoniazid?

Take all of the isoniazid that has been prescribed for you even if you begin to feel better. Your symptoms may begin to improve before the infection is completely treated.

Avoid alcohol while taking isoniazid. Alcohol may increase the risk of damage to the liver during isoniazid treatment.

Contact your doctor immediately if you experience numbness or tingling in the hands or feet, weakness, fatigue, loss of appetite, nausea and vomiting, yellowing of the skin or eyes, or darkening of the urine.

Warning

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.

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What is isoniazid?

Isoniazid is an antibiotic. It prevents tuberculous bacteria from multiplying in the body.

Isoniazid is used to treat and to prevent tuberculosis (TB).

Isoniazid may also be used for purposes other than those listed in this medication guide.

Precautions

Before taking this medication, tell your doctor if you have

  • ever had an allergic reaction to isoniazid,
  • kidney disease, or
  • liver disease.

You may not be able to take isoniazid, or you may require a dosage adjustment or special monitoring during treatment if you have any of the conditions listed above.

It is not known whether isoniazid will be harmful to an unborn baby. Do not take this medication without first talking to your doctor if you are pregnant or could become pregnant during treatment.

It is not known whether isoniazid will be harmful to a nursing baby. Do not take this medication without first talking to your doctor if you are breast-feeding a baby.

Avoid alcohol while taking isoniazid. Alcohol will increase the risk of damage to the liver during treatment with this medication.

Use caution with the foods listed below. They can interact with isoniazid and cause a reaction that includes a severe headache, large pupils, neck stiffness, nausea, vomiting, diarrhea, flushing, sweating, itching, irregular heartbeats, and chest pain. A reaction will not necessarily occur, but eat these foods with caution until you know if you will react to them. Call your doctor immediately if you experience any of these symptoms.

Eat the following foods with caution:

  • cheeses, including American, Blue, Boursault, Brick, Brie, Camembert, Cheddar, Emmenthaler, Gruyere, Mozzarella, Parmesan, Romano, Roquefort, Stilton, and Swiss;
  • sour cream and yogurt;
  • beef or chicken liver, fish, meats prepared with tenderizer, bologna, pepperoni, salami, summer sausage, game meat, meat extracts, caviar, dried fish, herring, shrimp paste, and tuna;
  • avocados, bananas, figs, raisins, and sauerkraut;
  • soy sauce, miso soup, bean curd, and fava beans;
  • yeast extracts;
  • ginseng;
  • chocolate;
  • caffeine (coffee, tea, cola, etc.); and
  • beer (alcoholic and nonalcoholic), red wine (especially Chianti), sherry, vermouth, and other distilled spirits.

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Instructions

Seek emergency medical attention if an overdose is suspected.

Symptoms of an isoniazid overdose include nausea, vomiting, dizziness, slurring of speech, blurred vision, visual hallucinations, seizures, coma, and death.

Take the missed dose as soon as you remember. If it is almost time for the next regularly scheduled dose, skip the missed dose and take the next one as directed. Do not take a double dose of this medication.

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Side Effects

If you experience any of the following serious side effects, stop taking isoniazid and seek emergency medical attention or contact your doctor immediately:

  • an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);
  • unusual weakness or fatigue;
  • nausea, vomiting, or loss of appetite;
  • abdominal pain;
  • yellow skin or eyes;
  • dark urine;
  • numbness or tingling in your hands or feet;
  • seizures;
  • blurred vision; or
  • confusion or abnormal behavior.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome. You may report side effects to FDA at 1-800-FDA-1088.

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Interactions

Before taking isoniazid, tell your doctor if you are taking any of the following drugs:

  • antacids. Aluminum salts will decrease the action of isoniazid. Do not take antacids that contain aluminum for 1 to 2 full hours before or after taking a dose of isoniazid.
  • ketoconazole (Nizoral) and itraconazole (Sporanox). Isoniazid may decrease the actions of these antifungal medicines. Therefore, a fungal infection may not be adequately treated.
  • rifampin (Rimactane, Rifadin) or rifabutin (Mycobutin).
  • disulfiram (Antabuse). Unusual behavior and coordination difficulties may occur if these medicines are taken together.

Isoniazid may increase the effects of the following medicines:

  • warfarin (Coumadin);
  • carbamazepine (Tegretol);
  • cycloserine (Seromycin);
  • phenytoin (Dilantin), ethotoin (Peganone), and mephenytoin (Mesantoin);
  • meperidine (Demerol);
  • benzodiazepines such as alprazolam (Xanax), diazepam (Valium), lorazepam (Ativan), and temazepam (Restoril);
  • theophylline (Theo-Dur, Theochron, Theolair, Elixophyllin, Slo-Phyllin, others);
  • ethionamide (Trecator-SC).

You may require a dosage adjustment or special monitoring if you are taking any of the medicines listed above.

Drugs other than those listed here may also interact with isoniazid. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including vitamins, minerals, and herbal products.

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Disclaimer

Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2004 Cerner Multum, Inc. Version 2.05. Revision date 8/23/04