Isoniazid is an antibiotic medication primarily used for the treatment and prevention of tuberculosis (TB). It is also known as isonicotinic acid hydrazide (INH) and has been a foundational drug in TB treatment regimens for decades since its discovery in the 1950s. This medication plays an important role in global public health efforts to control the spread of TB.
Primary Medical Uses
Isoniazid is an important part of tuberculosis management, addressing both active disease and latent infection. For individuals with active tuberculosis, isoniazid is typically part of a multi-drug regimen. This helps prevent the development of drug-resistant strains of the bacteria, as using isoniazid alone for active TB can lead to resistance.
Beyond treating active disease, isoniazid is also widely used to prevent the progression of latent tuberculosis infection (LTBI) to active TB. In LTBI, the TB bacteria are present in the body but are dormant and not causing illness or spreading to others. Treating LTBI with isoniazid reduces the risk of these dormant germs causing active disease. This preventive therapy is important for high-risk individuals, such as those with recent exposure to TB, those with certain medical conditions, or individuals with a positive TB skin test.
How It Works and How It’s Taken
Isoniazid functions as a prodrug, meaning it must be activated within bacterial cells to exert its effects against Mycobacterium tuberculosis. This activation occurs through a bacterial enzyme called catalase-peroxidase. Once activated, isoniazid interferes with the synthesis of mycolic acids, which are key components of the mycobacterial cell wall. By inhibiting mycolic acid production, isoniazid weakens the bacterial cell wall, leading to the death of the bacterial cell.
Isoniazid is available in various forms, including tablets, syrup, and injectable solutions. For adults, a common daily dose for treatment can be 300 mg, or a weight-based dose of 5 mg per kilogram of body weight, not exceeding 300 mg daily. Dosing can also involve intermittent regimens, such as 15 mg per kilogram of body weight (up to 900 mg) two or three times a week, often under directly observed therapy (DOT). Children’s dosages are weight-based, ranging from 10 to 20 mg per kilogram of body weight daily, up to 300 mg.
It is recommended to take isoniazid on an empty stomach, one to two hours before or after a meal, as food can reduce its absorption. The duration of treatment can be lengthy, often several months, and it is important to complete the entire prescribed course even if symptoms improve.
Important Patient Considerations
Taking isoniazid requires careful attention to potential side effects and interactions to ensure patient safety. Liver toxicity is a concern, ranging from mild liver enzyme elevations to severe hepatitis. Symptoms of liver problems include unusual tiredness, weakness, loss of appetite, nausea, vomiting, dark urine, and yellowing of the skin or eyes. These symptoms require immediate medical attention. Regular monitoring of liver function tests is often performed during treatment, especially for individuals over 50 or those with pre-existing liver conditions.
Another common side effect is peripheral neuropathy, which involves nerve damage leading to numbness, tingling, burning, or pain in the hands and feet. This side effect is linked to isoniazid’s interference with vitamin B6 (pyridoxine) metabolism. To prevent or reduce the risk of neuropathy, healthcare providers often recommend taking a vitamin B6 supplement alongside isoniazid. Dosage of pyridoxine ranges from 15 to 30 milligrams per day.
Isoniazid can interact with various substances, including alcohol. Regular alcohol consumption increases the risk of liver damage and can worsen nerve problems associated with isoniazid. It is advised to avoid alcohol while on this medication.
Certain foods high in tyramine or histamine, such as aged cheeses and cured meats, can also cause adverse reactions like headaches or flushing when consumed with isoniazid. Additionally, aluminum-containing antacids should be taken at least one hour after isoniazid, as they can hinder its absorption. Patients should inform their healthcare provider about all medications, supplements, and herbal products they are taking to avoid potential drug interactions.
Adherence to the prescribed treatment regimen is important for the effectiveness of isoniazid and to prevent the development of drug resistance. If a dose is missed, it should be taken as soon as remembered, unless it is almost time for the next scheduled dose, in which case the missed dose should be skipped; double doses should be avoided. Maintaining consistent communication with healthcare providers and attending all scheduled follow-up appointments are important for monitoring progress and addressing any concerns or side effects that may arise.