Isoniazid

By Medically reviewed by hellodoktor

Generic Name: Isoniazid Brand Name(s): Generics only. No brands available.

Uses

What is Isoniazid used for?

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). Unnecessary use or misuse of any antibiotic can lead to its decreased effectiveness.

How should I take 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.

How do I store Isoniazid?

Isoniazid is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store Isoniazid in the bathroom or the freezer. There may be different brands of Isoniazid that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush Isoniazid down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Isoniazid?

Before taking isoniazid, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: previous severe reaction from isoniazid (such as liver disease), liver disease, alcohol use, HIV infection, kidney disease, diabetes, numbness/tingling of arms/legs (peripheral neuropathy), recent childbirth.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Alcohol may increase the risk of liver disease. Avoid alcoholic beverages while using this medication.

This product may cause live bacterial vaccines (such as BCG vaccine) to not work as well. Therefore, do not have any immunizations/vaccinations while using this medication unless your doctor tells you to.

Liquid forms of this medication may contain sugar. Caution is advised if you have diabetes or any other condition that requires you to limit/avoid sugar. Ask your doctor or pharmacist about using this product safely.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This product passes into breast milk but is unlikely to harm a nursing infant. Consult your doctor before breast-feeding.

Is it safe during pregnancy or breast-feeding?

There are no adequate studies in women for determining risk when using this Isoniazid during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking Isoniazid. Isoniazid is pregnancy risk category C according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk,
  • B=No risk in some studies,
  • C=There may be some risk,
  • D=Positive evidence of risk,
  • X=Contraindicated,
  • N=Unknown

Side effects

What side effects can occur from Isoniazid?

Nausea/vomiting or stomach upset may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if any of these unlikely but serious side effects occur: numbness/tingling of arms/legs, painful/swollen joints.

Tell your doctor right away if any of these rare but seriousincreased thirst/urination, vision changes, easy bruising/bleeding, mental/mood changes (such as confusion, psychosis), seizures.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: fever that doesn’t go away, new or worsening lymph node swelling, rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.

Interactions

What drugs may interact with Isoniazid?

Some products that may interact with this drug include: acetaminophen, certain azole antifungals (itraconazole, ketoconazole), disulfiram, MAO inhibitors (isocarboxazid, linezolid, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, safinamide, selegiline, tranylcypromine), phenytoin, SSRI antidepressants (such as fluoxetine, sertraline), valproic acid.

This medication may interfere with certain laboratory tests (including urine glucose tests), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

Isoniazid may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Does food or alcohol interact with Isoniazid?

Isoniazid may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with Isoniazid?

Isoniazid may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Dosage

The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using this Isoniazid.

What is the dose of Isoniazid for an adult?

Usual Adult Dose for Tuberculosis – Active

Active infection: 5 mg/kg (up to 300 mg) IM or orally once a day, or 15 mg/kg (up to 900 mg) 2 to 3 times a week. Therapy is usually continued for 6 months, or 3 months beyond culture conversion (when given with rifampin and pyrazinamide).

Latent infection: 10-20 mg/kg/day orally once a day, not to exceed 300 mg/day

If isoniazid and pyrazinamide are used alone, isoniazid should be continued for 9 months. If the patient is HIV-positive, therapy should be continued for at least 9 months, or for 6 months beyond culture conversion. Longer duration of therapy should be considered for silico-, bone, and meningeal tuberculosis.

Usual Adult Dose for Tuberculosis – Prophylaxis

300 mg orally once a day or 900 mg orally 2 to 3 times a week. Isoniazid should be continued for 6 months to prevent the development of active tuberculosis in patients with no complicating factors. Patients with complicating factors such as HIV infection, diabetes, hematologic malignancy, or scars on chest X-ray should receive prophylaxis for 12 months.

Usual Adult Dose for Mycobacterium kansasii

600 to 900 mg IM or orally once a day.

Renal Dose Adjustments

CrCl less than 10 mL/min: Reduce dose by 50%.

Liver Dose Adjustments

If liver function tests exceed 3 to 5 times the upper limit of baseline, discontinue use of isoniazid therapy and monitor until liver function tests return to baseline. Symptoms of liver toxicity include anorexia, nausea, vomiting, dark urine, icterus, rash, persistent paresthesias of the hands and feet, persistent fatigue, weakness or fever greater than 3 days duration, and right upper quadrant abdominal tenderness.

Isoniazid therapy may be reinstituted when liver function tests return to baseline and symptoms of toxicity resolve.

Dose Adjustments

The dose should be reduced in severe hepatic disease.

Dialysis

Isoniazid is dialyzable (50% to 100%) by hemodialysis.

Other Comments

Pyridoxine, 50 mg orally once a day, may be administered with isoniazid to prevent the occurrence of peripheral neuropathy.

What is the dose of Isoniazid for a child?

Usual Pediatric Dose for Tuberculosis – Active

Oral, IM:

Infants, Children 40 kg or less, and Adolescents 14 years or less and less than 40 kg:

Treatment of active infection: CDC Recommendations: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly as part of a multidrug regimen.

Treatment of latent infection: 10 to 20 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 40 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly. Treatment duration: 9 months.

Primary prophylaxis for TB in HIV-exposed positive patients: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose twice weekly (maximum dose: 900 mg/day). Treatment duration: 9 months.

Usual Pediatric Dose for Tuberculosis – Latent

Oral, IM:

Infants, Children 40 kg or less, and Adolescents 14 years or less and less than 40 kg:

Treatment of active infection: CDC Recommendations: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly as part of a multidrug regimen.

Treatment of latent infection: 10 to 20 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 40 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly. Treatment duration: 9 months.

Primary prophylaxis for TB in HIV-exposed positive patients: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose twice weekly (maximum dose: 900 mg/day). Treatment duration: 9 months.

How is Isoniazid available?

Isoniazid is available in the following dosage forms and strengths:

  • Intramuscular solution,
  • Oral tablet,
  • Oral syrup.

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of Isoniazid, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: March 5, 2018 | Last Modified: September 12, 2019

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