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Drug Information For:


Ingredient Name:

ISONIAZID (eye-soe-NYE-a-zid)

Drug Manufacturer:


Common Uses:

This medicine is an antibacterial used to treat or prevent tuberculosis (TB) infection. If you are using this medicine to treat TB, it should be used along with other medicines.

Before Using This Medicine:

WARNING: THIS MEDICINE MAY CAUSE SEVERE AND SOMETIMES FATAL LIVER PROBLEMS (such as hepatitis). The risk of liver problems is greater in patients older than 35 years old. It may also be increased by daily use of alcohol, long-term liver problems, or unsanitary injectable drug use. Women, especially those who are black, hispanic, or have just had a baby, may also be at increased risk. Hepatitis can develop at any time during treatment but usually occurs during the first 3 months. Your doctor will monitor your liver function and discuss your progress every month. Contact your doctor right away if you develop unusual fatigue, weakness or fever that lasts longer than 3 days, general feeling of discomfort, loss of appetite, nausea, vomiting, numbness or tingling of the hands or feet, dark urine, yellowing of the skin or eyes, or stomach pain or tenderness. Patients with active liver problems should not use this medicine. Some medicines or medical conditions may interact with this medicine. INFORM YOUR DOCTOR OR PHARMACIST of all prescription and over-the-counter medicine that you are taking. ADDITIONAL MONITORING OF YOUR DOSE OR CONDITION may be needed if you are taking acetaminophen, anticoagulants (such as warfarin), carbamazepine, hydantoins (such as phenytoin), ketoconazole, rifampin, theophylline, or valproic acid. DO NOT START OR STOP any medicine without doctor or pharmacist approval. TELL YOUR DOCTOR if you are more than 35 years old, have recently given birth, or have previously taken this medicine. Inform your doctor if you have a history of liver problems, alcohol or other substance abuse, unsanitary injectable drug habits, or if you drink alcohol daily. Inform your doctor of any other medical conditions including diabetes, kidney problems, nerve problems (such as neuropathy) or if you are at risk of nerve problems, HIV, allergies, pregnancy, or breast-feeding. USE OF THIS MEDICINE IS NOT RECOMMENDED if you have severe liver damage, active liver disease, liver damage or severe side effects (such as drug fever, chills, or arthritis) from previous use of this medicine, or if you have a history of hepatitis caused by any medicine. Contact your doctor or pharmacist if you have any questions or concerns about taking this medicine.

How to Use This Medicine:

Follow the directions for using this medicine provided by your doctor. Use a measuring device marked for medicine dosing. Ask your pharmacist for help if you are unsure of how to measure this dose. TAKE THIS MEDICINE ON AN EMPTY STOMACH at least 1 hour before or 2 hours after a meal. IF YOU ALSO TAKE AN ANTACID, take this medicine at least 1 hour before you take the antacid. STORE THIS MEDICINE at room temperature between 68 and 77 degrees F (20 and 25 degrees C), in a tightly-closed container, away from heat and light. TO CLEAR UP YOUR INFECTION COMPLETELY, continue taking this medicine for the full course of treatment even if you feel well. Do not miss any doses. IF YOU MISS A DOSE OF THIS MEDICINE, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.


DO NOT TAKE THIS MEDICINE if you have had an allergic reaction to it or if you are allergic to any ingredient in this product. This medicine only works against TB bacteria. It does not treat viral infections (such as the common cold). Be sure to use this medicine for the full course of treatment. If you do not, the medicine may not clear up your infection completely. The bacteria could also become less sensitive to this or other medicines. This could make the infection harder to treat in the future. DO NOT STOP TAKING THIS MEDICINE without first checking with your doctor. Laboratory and/or medical tests, including liver function and eye exams may be performed to monitor your progress or to check for side effects. KEEP ALL DOCTOR AND LABORATORY APPOINTMENTS while you are taking this medicine. THIS MEDICINE MAY CAUSE nerve problems. Notify your doctor if you notice any unusual tingling in your hands or feet. The risk of developing nerve problems from this medicine may be increased if you have a history of diabetes, poor nutrition, or alcohol abuse. Your doctor may recommend that you also take vitamin B6 while you take this medicine. This may help to decrease your risk of nerve problems from this medicine. CHECK WITH YOUR DOCTOR before drinking alcohol while you are taking this medicine. DO NOT EAT FOODS HIGH IN TYRAMINE (such as aged cheeses, red wines, beer, certain meats and sausages, liver, sour cream, soy sauce, raisins, bananas, avocados) while you use this medicine because they may cause severe high blood pressure. Seek medical attention at once if symptoms of severe high blood pressure occur (such as severe headache, fast or irregular heartbeat, sore or stiff neck, nausea, vomiting, sweating, enlarged pupils, or sensitivity to light). DO NOT EAT FOODS HIGH IN HISTAMINE (such as skipjack, tuna, tropical fish) while you use this medicine because they may cause low blood pressure, irregular heartbeat, headache, sweating, or flushing. Contact your doctor at once if any of these symptoms occur. Ask your health care provider for a complete list of foods you should avoid while you are taking this medicine. BEFORE YOU BEGIN TAKING ANY NEW MEDICINE, either prescription or over-the-counter, check with your doctor or pharmacist. This includes acetaminophen and medicines containing acetaminophen. SOME PATIENTS MAY HAVE A GREATER RISK OF SEVERE LIVER PROBLEMS from this medicine, especially black women, hispanic women, and patients over 35 years old. Check with your doctor if you have questions about your risk of liver problems while taking this medicine. FOR WOMEN: IF YOU PLAN ON BECOMING PREGNANT, discuss with your doctor the benefits and risks of using this medicine during pregnancy. THIS MEDICINE IS EXCRETED in breast milk. IF YOU ARE OR WILL BE BREAST-FEEDING while you are using this medicine, check with your doctor or pharmacist to discuss the risks to your baby. IFYOU HAVE DIABETES, this medicine may affect your blood sugar. Check blood glucose levels closely and ask your doctor before adjusting the dose of your diabetes medicine.

Possible Side Effects:

A SIDE EFFECT that may occur while using this medicine is mild stomach upset. If it continues or is bothersome, check with your doctor. CHECK WITH YOUR DOCTOR AS SOON AS POSSIBLE if you experience changes in vision, memory problems, mood or mental changes, or symptoms of low vitamin B6 levels (such as scaly rash, cracks in the corners of the mouth, mouth redness or soreness, confusion, irritability). CONTACT YOUR DOCTOR IMMEDIATELY if you experience dark urine, fever or chills, general feeling of discomfort, increased thirst or urination, loss of appetite, nausea, vomiting, muscle or joint pain or swelling, seizures, stomach pain or tenderness, tingling or numbness of hands or feet, unusual tiredness or weakness, unusual bruising or bleeding, or yellowing of the skin or eyes. AN ALLERGIC REACTION to this medicine is unlikely, but seek immediate medical attention if it occurs. Symptoms of an allergic reaction include rash, itching, swelling, dizziness, or trouble breathing. If you notice other effects not listed above, contact your doctor, nurse, or pharmacist. This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your healthcare provider. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


If overdose is suspected, contact your local poison control center or emergency room immediately. Symptoms of overdose may include nausea, vomiting, dizziness, slurred speech, blurred vision, hallucinations, seizures, loss of consciousness, symptoms of high blood sugar (such as increased thirst or urination, rapid breathing, confusion, unusual drowsiness), and very slow breathing.

Additional Information:

If your symptoms do not improve or if they become worse, check with your doctor. DO NOT SHARE THIS MEDICINE with others for whom it was not prescribed. DO NOT USE THIS MEDICINE for other health conditions. KEEP THIS MEDICINE out of the reach of children and pets. IF USING THIS MEDICINE FOR AN EXTENDED PERIOD OF TIME, obtain refills before your supply runs out.

Copyright 2014 Wolters Kluwer Health, Inc.


- This information is not intended to substitute for professional medical advice. Be sure to contact your physician, pharmacist or other health care provider for more information about this medication. By searching these web site pages, you agree to our terms and conditions of use.