
Isoniazid
Product dosage: 300mg | |||
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Synonyms
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Isoniazid: The Gold Standard in Tuberculosis Treatment
Isoniazid is a first-line antituberculosis medication that represents the cornerstone of modern TB management. As a highly specific bactericidal agent against Mycobacterium tuberculosis, it has been instrumental in reducing global TB mortality rates since its introduction in the 1950s. This antibiotic remains essential for both active tuberculosis treatment and latent infection prevention, offering targeted action with a well-established safety profile when administered under proper medical supervision. Its continued relevance in global health underscores its efficacy and importance in combating one of humanity’s oldest infectious diseases.
Features
- Bactericidal activity against actively dividing mycobacteria
- High oral bioavailability with rapid absorption
- Concentration-dependent killing mechanism
- Specific activity against Mycobacterium tuberculosis complex
- Penetration into caseous material and body fluids
- Metabolic primarily through acetylation and hydrolysis
Benefits
- Superior bactericidal action: Rapidly reduces bacterial load in pulmonary and extrapulmonary tuberculosis
- Prevention of resistance development: Essential component in combination therapy to prevent emergence of drug-resistant strains
- Latent TB eradication: Effectively prevents progression from latent infection to active disease
- Central nervous system penetration: Reaches therapeutic concentrations in cerebrospinal fluid for meningeal TB treatment
- Proven long-term efficacy: Decades of clinical evidence supporting its effectiveness in TB control programs
- Cost-effective intervention: Affordable medication with significant public health impact
Common use
Isoniazid is primarily indicated for the treatment of all forms of active tuberculosis caused by susceptible strains of Mycobacterium tuberculosis. It must always be administered in combination with other antituberculosis drugs to prevent the development of drug resistance. Additionally, it is used as monotherapy for the treatment of latent tuberculosis infection in individuals at high risk of progression to active disease. The medication is also employed as preventive therapy in HIV-positive individuals with latent TB infection and in recent contacts of infectious TB cases. Its use extends to chemoprophylaxis in specific high-risk populations, including patients undergoing immunosuppressive therapy and those with radiographic evidence of previous healed tuberculosis.
Dosage and direction
Active tuberculosis: 5 mg/kg (usual adult dose 300 mg) orally once daily, or 15 mg/kg (maximum 900 mg) orally two or three times weekly as part of combination therapy. Treatment duration typically ranges from 6 to 9 months depending on regimen.
Latent tuberculosis: 5 mg/kg (usual adult dose 300 mg) orally once daily, or 15 mg/kg (maximum 900 mg) orally twice weekly for 6 to 9 months. Alternative regimens include daily administration for 9 months being most effective.
Pediatric dosing: 10-15 mg/kg (maximum 300 mg) orally once daily, or 20-40 mg/kg (maximum 900 mg) orally twice weekly.
Administration should occur on an empty stomach, preferably 1 hour before or 2 hours after meals, to ensure optimal absorption. Dosage adjustments are necessary in patients with slow acetylator status and those with hepatic impairment. Weekly directly observed therapy (DOT) is recommended for intermittent dosing regimens to ensure adherence.
Precautions
Baseline assessment should include complete blood count, liver function tests, and renal function tests. Monthly monitoring of liver enzymes is mandatory during treatment. Patients should be educated to report immediately any symptoms of hepatitis, including fatigue, weakness, nausea, vomiting, dark urine, or jaundice. Peripheral neuropathy risk necessitates pyridoxine (vitamin B6) supplementation, particularly in malnourished patients, alcoholics, diabetics, and those with HIV infection. Regular visual acuity testing is recommended as isoniazid may cause optic neuritis. Alcohol consumption should be avoided due to increased risk of hepatitis. Blood glucose monitoring is advised in diabetic patients as hyperglycemia may occur.
Contraindications
Absolute contraindications include previous severe hypersensitivity reactions to isoniazid, acute liver disease of any etiology, or previous isoniazid-associated hepatic injury. Severe adverse reactions such as drug-induced hepatitis, fever, rash, or arthralgia during previous isoniazid therapy preclude reuse. The medication is contraindicated in patients with severe peripheral neuropathy unless no alternative exists and appropriate prophylaxis with pyridoxine is provided. Concomitant use with carbamazepine or phenytoin requires careful monitoring due to increased risk of toxicity.
Possible side effect
Common (≥1%): Peripheral neuropathy (dose-related), elevated liver enzymes, nausea, vomiting, epigastric distress, dizziness, headache, fever, rash, and pruritus.
Serious (<1%): Hepatitis (age-related risk), optic neuritis with blurred vision and eye pain, agranulocytosis, hemolytic anemia, aplastic anemia, hypersensitivity reactions including Stevens-Johnson syndrome, drug-induced lupus erythematosus, seizures, psychosis, and gynecomastia.
Metabolic effects: Pyridoxine deficiency, pellagra-like syndrome, hyperglycemia, metabolic acidosis, and hypocalcemia.
Neurological effects: Memory impairment, toxic encephalopathy, and anxiety disorders have been reported with long-term use.
Drug interaction
Potentially significant interactions: Concurrent administration with carbamazepine, phenytoin, or valproic acid increases anticonvulsant levels requiring dosage adjustment. Aluminum-containing antacids decrease isoniazid absorption. Concomitant use with disulfiram may cause coordination difficulties and psychotic episodes. Rifampin coadministration increases risk of hepatotoxicity. Ketoconazole levels may be decreased. Enflurane metabolism may be inhibited, potentially increasing fluoride concentrations and nephrotoxicity risk.
Moderate interactions: May potentiate effects of warfarin requiring INR monitoring. Theophylline levels may be increased. Cycloserine coadministration increases CNS toxicity risk. Tyramine-containing foods may cause exaggerated pressor response. Corticosteroids may decrease isoniazid efficacy.
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next scheduled dose. Doubling of doses should be avoided. For patients on daily therapy, if more than 14 consecutive days are missed, physician consultation is required before resuming treatment. Those on twice-weekly regimens should not take the medication if more than 3 days have passed since the missed dose; instead, they should wait until the next scheduled dose. Consistent adherence is critical to prevent treatment failure and development of drug resistance.
Overdose
Acute overdose of 1.5g or more may cause symptoms within 30 minutes to 3 hours. Early manifestations include nausea, vomiting, dizziness, slurred speech, blurred vision, and visual hallucinations. Severe overdose may progress to seizures, metabolic acidosis, respiratory distress, coma, and death. Treatment is supportive with immediate gastric lavage if presented within hours of ingestion. Activated charcoal may be effective. Pyridoxine (vitamin B6) is the specific antidote, administered gram-for-gram with the amount of isoniazid ingested. Intravenous diazepam is indicated for seizure control. Hemodialysis may be beneficial in severe cases, particularly with metabolic acidosis.
Storage
Store at controlled room temperature between 20°C to 25°C (68°F to 77°F). Protect from light and moisture. Keep container tightly closed. Do not store in bathroom cabinets where humidity may affect stability. Keep out of reach of children and pets. Do not use beyond expiration date printed on packaging. Properly discard any unused medication after treatment completion. Do not flush medications down toilet or pour into drain unless instructed to do so.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Isoniazid is a prescription medication that must be used under appropriate medical supervision. Healthcare providers should be consulted for proper diagnosis, treatment recommendations, and monitoring. The prescribing information provided here may not include all possible uses, directions, precautions, or interactions. Actual patient treatment should be based on comprehensive clinical assessment and current treatment guidelines. Never discontinue or change dosage without medical consultation.
Reviews
Clinical efficacy: “Isoniazid remains the backbone of tuberculosis treatment regimens worldwide. In our TB control program, we’ve observed success rates exceeding 95% when combined with other first-line drugs and proper adherence monitoring.” - Dr. Elena Rodriguez, Infectious Disease Specialist
Safety profile: “While hepatotoxicity is a concern, particularly in older patients, routine monitoring allows for early detection and intervention. The benefits in TB eradication far outweigh the risks when properly managed.” - Pharmacist James Chen, TB Clinic
Patient experience: “After completing the 6-month regimen with isoniazid combination therapy, my follow-up cultures were negative. The peripheral neuropathy was manageable with pyridoxine supplementation.” - Patient, 42-year-old male
Public health impact: “As a WHO-recommended essential medicine, isoniazid has been instrumental in reducing TB incidence in developing countries. Its inclusion in fixed-dose combinations has improved treatment adherence significantly.” - Public Health Official, Global TB Program