Adult: In combination with other antitubercular agents: Usual dose: 5 mg/kg (up to 300 mg) daily as a single dose, or 15 mg/kg (up to 900 mg daily) given 2 or 3 times weekly via slow IM or IV inj. Doses are for both the initial and continuation phases. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen. Child: In combination with other antitubercular agents: Usual dose: 10-15 mg/kg (up to 300 mg) daily as a single dose, or 20-40 mg/kg (up to 900 mg daily) given 2 or 3 times weekly via slow IM or IV inj. Doses are for both the initial and continuation phases. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen.
Intramuscular Latent tuberculosis infection
Adult: Prophylactic therapy of TB in at-risk patients (refer to current local therapy guidelines to identify appropriate candidates for preventive treatment). Usual monotherapy dose: 300 mg daily as a single dose via inj for 6 months; or 5 mg/kg (up to 300 mg) daily or 15 mg/kg (up to 900 mg) 2 times weekly via inj for 6 or 9 months. Alternatively, an oral regimen in combination with rifampicin for 3 months has been used. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen.
Adult: In combination with other antitubercular agents: Usual dose: 5 mg/kg (up to 300 mg) daily in single or divided doses. For intermittent treatment regimens: 15 mg/kg given 2 or 3 times weekly; alternatively, 15 mg/kg (up to 900 mg daily) administered once weekly, or 2 or 3 times weekly. Doses are for both the initial and continuation phases. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen. Child: In combination with other antitubercular agents: Usual dose: 10-15 mg/kg (up to 300 mg) daily in single or divided doses; alternatively, 20-30 mg/kg (up to 900 mg daily) given 2 or 3 times weekly. Doses are for both the initial and continuation phases. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen.
Oral Latent tuberculosis infection
Adult: Prophylactic therapy of TB in at-risk patients (refer to current local therapy guidelines to identify appropriate candidates for preventive treatment). Usual monotherapy dose: 300 mg daily as a single dose for 6 months; or 5 mg/kg (up to 300 mg) daily or 15 mg/kg (up to 900 mg) 2 times weekly for 6 or 9 months. Alternatively, a regimen in combination with rifampicin for 3 months has been used. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen. Child: Prophylactic therapy of TB in at-risk patients (refer to current local therapy guidelines to identify appropriate candidates for preventive treatment). Usual monotherapy dose: 10 mg/kg (up to 300 mg) daily as a single dose, or 20-40 mg/kg (up to 900 mg) 2 times weekly for 6 or 9 months. Alternatively, a regimen in combination with rifampicin for 3 months has been used. Dosage, regimen, and therapy duration recommendations may vary among individual products or between countries. Refer to local official treatment guidelines for the dosage selection, duration of therapy, and content of the combination regimen.
Special Patient Group
Isoniazid is primarily metabolised via acetylation and dehydrazination. Acetylation rate does not significantly alter the effectiveness of isoniazid; however, it is genetically determined. Approx 50% of African Americans and Caucasians are considered as slow inactivators or acetylators, while most of Asians and Eskimos are considered rapid inactivators or acetylators.
According to the FDA-approved labels for isoniazid, individuals known as slow acetylators or inactivators may have increased blood levels of isoniazid and may be at higher risk for its toxic reactions.
Renal Impairment
IM/IV Pulmonary tuberculosis; Extrapulmonary tuberculosis
Severe: Dose reduction may be needed. Haemodialysis: Administer immediately after haemodialysis.
Administration
Should be taken on an empty stomach. Best taken on an empty stomach 1 hr before or 2 hr after meals. May be taken w/ meals to reduce GI discomfort.
Contraindications
Hypersensitivity. History of isoniazid-associated hepatic injury or severe adverse reactions to isoniazid, drug-induced hepatitis, acute liver disease of any aetiology.
Special Precautions
Patient with peripheral neuropathy, risk factors for peripheral neuropathy (e.g. diabetes mellitus, chronic alcoholism, HIV infection, nutritional deficiency), history of psychosis, epilepsy, porphyria, chronic liver disease. Coadministration with pyridoxine is recommended in all patients at the start of therapy, particularly in those who are at risk of neuropathy or pyridoxine deficiency. Black and Hispanic women, particularly during the post-partum period. Slow acetylator. Hepatic and severe renal impairment. Children. Pregnancy and lactation.
Adverse Reactions
Significant: Peripheral neuropathy, decreased folic acid absorption, pyridoxine deficiency. Blood and lymphatic system disorders: Aplastic, sideroblastic, or haemolytic anaemia, agranulocytosis, eosinophilia, thrombocytopenia. Ear and labyrinth disorders: Vertigo, tinnitus, deafness. Eye disorders: Optic neuritis or atrophy. Gastrointestinal disorders: Constipation, nausea, vomiting, dry mouth, epigastric distress, acute pancreatitis. Hepatobiliary disorders: Jaundice. Immune system disorders: Hypersensitivity reactions. Investigations: Increased serum transaminases. Metabolism and nutrition disorders: Hyperglycaemia, metabolic acidosis, nicotinic acid deficiency. Musculoskeletal and connective tissue disorders: SLE, lupus-like syndrome. Nervous system disorders: Seizure. Psychiatric disorders: Increased mood, psychotic reactions. Renal and urinary disorders: Dysuria. Reproductive system and breast disorders: Gynaecomastia. Skin and subcutaneous tissue disorders: Alopecia, rash, exfoliative dermatitis, Stevens-Johnson syndrome. Rarely, toxic epidermal necrolysis. Potentially Fatal: Hepatotoxicity (e.g. severe hepatitis, hepatic necrosis).
Perform culture and susceptibility tests; consult local institutional recommendations before treatment initiation due to antibiotic resistance risks. Monitor LFTs at baseline and periodically during treatment (more frequent particularly in patients at risk of hepatitis); renal function prior to treatment initiation; sputum cultures monthly (until 2 consecutive negative cultures); prodromal signs of hepatitis. Perform ophthalmologic exam during treatment if visual symptoms occur. Additionally, perform a monthly clinical evaluation for latent TB infection therapy.
Overdosage
Symptoms: Nausea, vomiting, vertigo, dizziness, slurred speech, blurred vision, visual hallucinations (including bright colours and strange designs), metabolic acidosis, acetonuria and hyperglycaemia. CNS depression, seizures and respiratory distress that may progress rapidly from stupor to coma may occur after marked overdosage. Management: Symptomatic and supportive treatment. Give activated charcoal and perform gastric lavage. Secure the airway and ensure adequate ventilation. Administer IV anticonvulsants for seizures and IV pyridoxine as clinically indicated based on the ingested dose. Correct acidosis with Na bicarbonate. May perform forced diuresis, haemodialysis and peritoneal dialysis if necessary.
Drug Interactions
May increase induction of liver function abnormalities with rifampicin. Inhibits hepatic metabolism resulting in increased toxicity of antiepileptic (e.g. carbamazepine, ethosuximide, phenytoin, primidone), benzodiazepines (e.g. diazepam, triazolam), chlorzoxazone, disulfiram. Increased metabolism of enflurane, resulting in potentially nephrotoxic levels of fluoride. Increased concentrations and enhanced effects or toxicity of clofazimine, cycloserine and warfarin. Increased risk of peripheral neuropathy with zalcitabine and stavudine. May reduce the therapeutic effects of levodopa. May decrease serum concentrations of itraconazole, ketoconzaole. Reduced absorption with Al-containing antacids. Concurrent use with paracetamol may cause severe paracetamol toxicity. May increase the plasma levels of theophylline and valproate. Decreased plasma levels with prednisolone.
Food Interaction
Reduced bioavailability, and rate and extent of absorption with food. Avoid tyramine-containing (e.g. cheese, red wine) and histamine-containing foods (e.g. skipjack, tuna, other tropical fish) as they may cause exaggerated responses (e.g. headache, sweating, palpitations, flushing, hypotension). Hepatotoxic effects may be enhanced by alcohol.
Lab Interference
May cause false-positive results for urinary glucose with cupric sulfate solutions (e.g. Benedict’s reagent, Clinitest®).
Action
Description: Mechanism of Action: Isoniazid is a isonicotinic acid hydrazide derivative that inhibits the synthesis of mycolic acids, an essential components of the bacterial cell wall. It is bactericidal at therapeutic levels against the actively growing extracellular and intracellular Mycobacterium tuberculosis organisms.
Synonym: isonicotinic acid hydrazide. Pharmacokinetics: Absorption: Readily and completely absorbed from the gastrointestinal tract and after IM inj. Reduced rate and extent of absorption with food. Time to peak plasma concentration: 1-2 hours (oral). Distribution: Distributed in all body tissues and fluids, including CSF. Crosses the placenta and enters breast milk. Plasma protein binding: Approx 10-15%. Metabolism: Metabolised in the liver and small intestine via acetylation to acetylisoniazid by N-acetyltransferase; undergoes further hydrolysis to isonicotinic acid and monoacetylhydrazine. Isonicotinic acid is then conjugated with glycine into isonicotinyl glycine while monoacetylhydrazine is further acetylated to diacetylhydrazine. Unmetabolised isoniazid is conjugated to hydrazones. Excretion: Via urine (75-95% as unchanged drug and metabolites); faeces and saliva (small amounts). Elimination half-life: 0.5-1.6 hours (fast acetylators); 2-5 hours (slow acetylators).
Chemical Structure
Isoniazid Source: National Center for Biotechnology Information. PubChem Database. Isoniazid, CID=3767, https://pubchem.ncbi.nlm.nih.gov/compound/Isoniazid (accessed on Jan. 21, 2020)
Storage
Store between 20-25°C. Protect from moisture and light.
J04AC01 - isoniazid ; Belongs to the class of hydrazides. Used in the systemic treatment of tuberculosis.
References
Annotation of FDA Label for Isoniazid/Pyrazinamide/Rifampin and NAT2. Pharmacogenomics Knowledgebase (PharmGKB). https://www.pharmgkb.org/. Accessed 02/09/2021.Anon. Isoniazid. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 02/09/2021.Anon. Isoniazid. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 02/09/2021.Buckingham R (ed). Isoniazid. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 02/09/2021.Isoniazid 50 mg/2 mL Solution for Injection (Alliance Pharmaceuticals Ltd). MHRA. https://products.mhra.gov.uk. Accessed 02/09/2021.Isoniazid Injection, Solution (Sandoz Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 02/09/2021.Isoniazid Solution (CMP Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 02/09/2021.Isoniazid Tablet (Lannett Company, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 02/09/2021.Isoniazid Tablet (Pharmaniaga Manufacturing Berhad). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my. Accessed 02/09/2021.Isoniazid Tablets BP 100 mg (RPH Pharmaceuticals AB). MHRA. https://products.mhra.gov.uk. Accessed 02/09/2021.Joint Formulary Committee. Isoniazid. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 02/09/2021.
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