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Isoniazid

Oral
Intramuscular
Class
Antimycobacterials
Subclass
Mycolic acid synthesis inhibitors
Substance name
Isoniazid, isonicotinic acid hydrazide, INH
Common formulations
Tablet
Dosage and administration
Adults patients
Latent tuberculosis in patients with HIV infection
•
300 mg PO daily for 9 months
Administered in combination with pyridoxine. Do not take with food. Avoid foods containing tyramine (red wine, cheese) or histamine (skipjack, tune, or other fish).
M. kansasii • Off-label
•
Maintenance: 5 mg/kg PO daily
•
Maximum: 300 mg per day
Do not take with food. Avoid tyramine (eg. red wine, cheese) and histamine (skipjack, tune, or other fish) containing foods.
Indications for use
Labeled indications
Adults
•
Treatment of latent tuberculosis
•
Treatment of latent tuberculosis in patients with HIV infection
•
Treatment of tuberculosis (intensive phase)
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Treatment of tuberculosis in patients with HIV infection (intensive phase)
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Adjunctive treatment for active tuberculosis in patients with HIV infection (continuation phase)
•
Adjunctive treatment for tuberculosis (continuation phase)
Off-label indications
Adults
•
Treatment of M. kansasii
Safety risks
Boxed warnings
Hepatitis
•
Use extreme caution in all patients, especially those with an increased risk of hepatitis, such as individuals with daily alcohol use, chronic liver disease, or those who use injection drugs. Regularly monitor liver function and conduct clinical evaluations at monthly intervals. For patients aged 35 and older, measure liver enzymes at baseline and periodically throughout treatment. Instruct patients to immediately report any signs or symptoms indicative of liver damage or adverse effects, such as unexplained anorexia, nausea, vomiting, dark urine, jaundice, rash, persistent paresthesias of the hands and feet, persistent fatigue, weakness, fever lasting more than 3 days, or RUQ abdominal tenderness. If liver function abnormalities exceed three to five times the ULN, consider discontinuing isoniazid. Promptly discontinue the drug if symptoms of hepatic damage or adverse reactions are observed, as continued use may lead to more severe liver damage. Patients with tuberculosis who experience isoniazid-induced hepatitis should receive alternative treatments, and if isoniazid is reintroduced after recovery, it should be done in gradually increasing doses, with prompt discontinuation if liver issues recur.
Contraindications
Hypersensitivity to isoniazid or its components
Acute liver disease
History of isoniazid-associated hepatic injury
Serious adverse reactions to isoniazid such as drug fever, chills, arthritis
Warnings and precautions
Jaundice, increased serum transaminases, increased serum TBIL, drug-induced liver injury
•
Use caution in patients aged 35 years or older, those with heavy alcohol consumption, chronic hepatitis B or C, HIV, underlying liver disease, history of liver transplant, malnutrition, postpartum females, or in those taking concurrent hepatotoxic medications. Additionally, be cautious in individuals with genetic polymorphisms (e.g., CYP450 2E1 and N-acetyltransferase 2).
Peripheral neuropathy
•
Use caution in patients with preexisting peripheral neuropathy, those on high doses, or those with conditions that predispose to peripheral neuropathy (e.g., alcoholism, diabetes, CKD, HIV, advanced age, or malnutrition).
Specific populations
Renal impairment
CrCl 0-90 mL/min
•
Use acceptable. No dose adjustment required.
Renal replacement therapy
Any modality
•
Use acceptable. No dose adjustment required.
Hepatic impairment
Any severity
•
Use with caution. Monitor serum aminotransferases. Monitor for toxicity.
Pregnancy and breastfeeding
Pregnancy
All trimesters • Australia Category: A
•
Use only if benefits outweigh potential risks. Evidence of fetal harm in animals. Isoniazid is recommended for treating active TB in pregnant patients with moderate to high disease risk. Preventative therapy is typically started postpartum. Monitor exposed neonates for adverse events. Due to increased hepatotoxicity risk, perform monthly transaminase monitoring, and use pyridoxine to prevent peripheral neurotoxicity.
Breastfeeding
Acceptable for use during breastfeeding.
•
All breastfeeding mothers on isoniazid should take 25 mg of oral pyridoxine daily.
Very low levels in breastfed infants (< 5%).
May potentially cause adverse effects in breastfed infants.
Adverse reactions
Very common > 10%
•
↑ liver enzymes
Common 1-10%
•
Peripheral neuropathy, nausea, vomiting
Unknown frequency
•
Acute generalized exanthematous pustulosis, acute pancreatitis, agranulocytosis, aplastic anemia, bronchospasm, conjunctivitis, DRESS syndrome, ↓ blood neutrophil count, ↓ platelet count, encephalopathy, exfoliative dermatitis, gynecomastia, hemolytic anemia, hepatitis, hypotension, ↑ blood eosinophil count, ↑ blood glucose, ↑ serum TBIL, interstitial nephritis, jaundice, lymphadenopathy, metabolic acidosis, optic atrophy, optic neuritis, psychosis, purpura, abdominal pain, chest pain, chills, cough, dyspnea, fever, lupus-like symptoms, memory impairment, musculoskeletal pain, palpitations, paresthesia, seizure, skin rash, syncope, sideroblastic anemia, Stevens-Johnson syndrome, toxic epidermal necrolysis, vasculitis, vitamin B6 deficiency, vitamin D deficiency
Interactions
Drug(s)
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