Isoniazid

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.

Isoniazid 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.

Adult and Pediatric Dosage Forms and Strengths

Tablets

• 50mg
• 100mg
• 300mg

Oral syrup

• 50mg/5mL

Injectable solution

• 100mg/mL

Dosage Considerations – Should be Given as Follows:

Latent Tuberculosis Infection

Treatment of latent tuberculosis (TB) infection greatly reduces the risk that TB infection will progress to active disease

Adult:

Greater than 30 kg: 300 mg orally once/day for 9 months

3-month regimen

Recommended for patients aged 12 years and older who are at high risk for developing TB disease including anyone who has had recent exposure to contagious TB, conversion from negative to positive on a test for TB infection, or a chest X-ray indicating prior TB disease Persons with HIV who are otherwise healthy and not taking antiretrovirals may also use this regimen 900 mg orally once weekly for 3 months (administer with rifapentine 900 mg once weekly) Administered as Directly Observed Treatment (DOT) Not recommended for children under 2 years, pregnant women or women planning to become pregnant, HIV-infected persons taking antiretrovirals, and patients whose TB infection is presumed to be the result of exposure to a person with TB disease that is resistant to 1 of the 2 drugs References: CDC MMWR 2011;60:1650-3 and NEJM 2011;365:2155-2166

Pediatric:

10-15 mg/kg orally once/day; not to exceed 300 mg/day

3-month regimen

Recommended for patients aged 12 years and older who are at high risk for developing TB disease including anyone who has had recent exposure to contagious TB, conversion from negative to positive on a test for TB infection, or a chest X-ray indicating prior TB disease Use for children aged 2-11 years and patients with underlying conditions associated with TB should be considered on a case-by-case basis; preferred regimen for this age group is daily isoniazid for 9 months Not recommended for children under 2 years Children over 12 years: isoniazid 900 mg orally plus rifapentine 900 mg orally once weekly for 3 months References: CDC MMWR 2011;60:1650-3 and NEJM 2011;365:2155-2166

Active Tuberculosis Disease

Adult:

5 mg/kg orally/intramuscularly once/day, not to exceed 300 mg once/day

15 mg/kg orally/intramuscularly up; not to exceed 900 mg 1-3 times/week

Pediatric:

10-15 mg/kg orally once/day; not to exceed 300 mg/day OR

20-30 mg/kg (up to 900 mg) 2 times/week

Used in multi-drug regimen containing rifampin (or rifabutin or rifapentin), pyrazinamide, and ethambutol

Duration of treatment dependent on regimen consisting of an initial phase of treatment and a continuation phase of treatment

Note: Daily treatment has best results for HIV positive individuals

See Also Combos

With rifampin (Rifamate)

With rifampin and pyrizinamide (Rifater)

Other Indications and Uses

Newly infected patients

Household members and close associates of people recently diagnosed with tuberculosis (TB)

Positive TB skin test with positive non-progressive chest X-ray

Positive TB skin test with underlying disease or immunosuppression

Positive TB skin test, younger than 35 years old; older than 35 years old weigh use against risk of hepatitis

Common side effects of isoniazid include:

• Mild increase in liver function tests (LFTs)
• Numbness/tingling/pain in extremities (dose-related incidence)
• Loss of appetite
• Nausea
• Vomiting
• Stomach pain or upset
• Weakness
• Dizziness
• Slurred speech
• Lethargy

Hepatitis (symptoms include loss of appetite, nausea, vomiting, fatigue, feeling unwell [malaise], and weakness)

• Progressive liver damage (incidence increases with age)
• Overactive reflexes

Fever Rash

Less common side effects of isoniazid include:

• Agranulocytosis
• Anemia
• Megaloblastic anemia
• Low platelet count (thrombocytopenia)
• Systemic lupus erythematosus
• Seizures

Other side effects of isoniazid include:

• Pancreatitis
• Toxic epidermal necrolysis
• Drug reaction with eosinophilia syndrome (DRESS)

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

Severe interactions of isoniazid include:

• cobimetinib
• conivaptan
• dihydroergotamine
• dihydroergotamine intranasal
• eliglustat
• flibanserin
• itraconazole
• ivabradine
• ketoconazole
• lomitapide
• lovastatin
• lurasidone
• naloxegol
• regorafenib
• venetoclax

Isoniazid has serious interactions with at least 76 different drugs.

Isoniazid has moderate interactions with at least 238 different drugs.

Isoniazid has mild interactions with at least 92 different drugs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

Warnings

Severe and sometimes fatal hepatitis may occur within the first 3 months of treatment and many months after treatment. Risk is related to age and increased with daily alcohol consumption.

Patients should be instructed about signs and symptoms of hepatitis.

This medication contains isoniazid. Do not take isoniazid if you are allergic to isoniazid or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Contraindications

Previous isoniazid hepatic injury or reaction; acute liver disease; pancreatitis

Hypersensitivity

Isoniazid is contraindicated in patients who develop severe hypersensitivity reactions, including drug-induced hepatitis; previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid such as drug fever, chills, arthritis; and acute liver disease of any etiology

Effects of Drug Abuse

No information available.

Short-Term Effects

• See "What Are Side Effects Associated with Using Isonaizid?"

Long-Term Effects

Severe and sometimes fatal hepatitis may occur within the first 3 months of treatment and many months after treatment. Risk is related to age and increased with daily alcohol consumption.

• See "What Are Side Effects Associated with Using Isonaizid?"

Cautions

Alcohol or illicit injectable drug use, predisposition to neuropathy, malnourished, severe renal impairment, chronic liver disease.

Use with other anti-tuberculosis (TB) agents.

Give pyridoxine (B6) concurrently for pregnant women, malnourished patients or those with neuropathic diathesis.

Alcohol use, renal or hepatic dysfunction will affect serum levels.

Pregnancy and Lactation

Use isoniazid with caution during pregnancy if benefits outweigh risks. Animal studies show risk and human studies are not available or neither animal nor human studies were done.

Isoniazid is distributed into breast milk but is considered safe for nursing infants.