Warnings:

Isoniazid has rarely caused very serious (possibly fatal) liver disease. The risk of liver disease is increased in people who are 35 years and older, who use alcohol or illegal injection drugs, or who currently have long-term liver problems. Tell your doctor right away if you develop symptoms of liver disease, including persistent nausea/vomiting, severe stomach/abdominal pain, unusual weakness/tiredness, dark urine, yellowing eyes/skin.

Your doctor should order liver function tests while you are taking this medication. Keep all medical and laboratory appointments.

Uses

Isoniazid is used with other medications to treat active tuberculosis (TB) infections. It is also used alone to prevent active TB infections in people who may be infected with the bacteria (people with positive TB skin test). Isoniazid is an antibiotic and works by stopping the growth of bacteria.This antibiotic treats only bacterial infections. It will not work for viral infections (such as common cold, flu). Using any antibiotic when it is not needed can cause it to not work for future infections.

How to use Isoniazid

Take this medication by mouth on an empty stomach (1 hour before or 2 hours after meals) as directed by your doctor. If you are using the liquid form of this medication, carefully measure the dose using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose.

If you also take antacids that contain aluminum, take this medication at least 1 hour before the antacid.

Dosage is based on your age, weight, medical condition, and response to treatment.

For the best effect, take this drug at evenly spaced times. If you are taking this medication daily, take it at the same time each day. If you are taking this medication on a weekly schedule, take it on the same day(s) of the week and at the same time each day. Mark the days on the calendar when you need to take the medication.

Continue to take this medication (and other TB medications) until the full prescribed amount is finished, even if symptoms disappear. Stopping the medication too early or skipping doses may allow the bacteria to continue to grow, which may result in a return of the infection and cause the infection to be more difficult to treat (resistant).

Your doctor may also direct you to take vitamin B6 (pyridoxine) to help prevent certain side effects (such as nerve problems) from isoniazid. Follow your doctor's instructions carefully.

Isoniazid may interact with foods containing tyramine/histamine (such as cheese, red wine, certain types of fish). This interaction may cause increased blood pressure, flushing of the skin, headache, dizziness, or fast/pounding heartbeat. Tell your doctor right away if any of these symptoms occur. Your doctor may recommend that you follow a special diet while taking this medication. Consult your doctor for more details.

Tell your doctor if your condition persists or worsens.

Drug Survey

Are you currently using Isoniazid?

This survey is being conducted by the WebMD marketing sciences department.

Free RX Coupon

Save up to 80% on your prescriptions.

Available coupons

Save up to 80% on your prescription with WebMDRx

Selected from data included with permission and copyrighted by First Databank, Inc. This copyrighted material has been downloaded from a licensed data provider and is not for distribution, except as may be authorized by the applicable terms of use.

CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.