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What is this medication?

Antitubercular Agent

Isoniazid is indicated for treatment of active tuberculosis infections; latent tuberculosis infection.

Severe and sometimes fatal hepatitis associated with isoniazid therapy has been reported and may occur or may develop even after many months of treatment. The risk of developing hepatitis is age related. Approximate case rates by age are as follows: less than 1/1,000 for persons younger than 20 years of age, 3/1,000 for persons in the 20 to 34 year age group, 12/1,000 for persons in the 35 to 49 year age group, 23/1,000 for persons in the 50 to 64 year age group, and 8/1,000 for persons older than 65 years. The risk of hepatitis is increased with daily consumption of alcohol. Precise data to provide a fatality rate for isoniazid-related hepatitis are not available; however, in a US Public Health Service surveillance study of 13,838 persons taking isoniazid, there were 8 deaths among 174 cases of hepatitis.

Therefore, carefully monitor patients given isoniazid and interview patients at monthly intervals. For persons 35 years and older, in addition to monthly symptom reviews, measure hepatic enzymes (specifically, AST and ALT) prior to starting isoniazid therapy and periodically throughout treatment. Isoniazid-associated hepatitis usually occurs during the first 3 months of treatment. Usually, enzyme levels return to normal despite continuance of drug, but, in some cases, progressive liver dysfunction occurs. Other factors associated with an increased risk of hepatitis include daily use of alcohol, chronic liver disease, and injection drug use. A recent report suggests an increased risk of fatal hepatitis associated with isoniazid among women, particularly black and Hispanic women. The risk may also be increased during the postpartum period. Consider more careful monitoring in these groups, possibly including more frequent laboratory monitoring. If abnormalities of liver function exceed 3 to 5 times the upper limit of normal (ULN), strongly consider discontinuation of isoniazid. Liver function tests are not a substitute for a clinical evaluation at monthly intervals or for the prompt assessment of signs or symptoms of adverse reactions occurring between regularly scheduled evaluations. Instruct patients to immediately report signs or symptoms consistent with liver damage or other adverse reactions. These include any of the following: unexplained anorexia, nausea, vomiting, dark urine, icterus, rash, persistent paresthesia of the hands and feet, persistent fatigue, weakness or fever of greater than 3-day duration or abdominal tenderness, especially right upper quadrant discomfort. If these symptoms appear or if signs suggestive of hepatic damage are detected, promptly discontinue isoniazid, because continued use of the drug in these cases has been reported to cause a more severe form of liver damage.

Give patients with tuberculosis who have hepatitis attributed to isoniazid appropriate treatment with alternative drugs. If isoniazid must be reinstituted, do so only after symptoms and laboratory abnormalities have cleared. Restart the drug in very small and gradually increasing doses and withdraw immediately if there is any indication of recurrent liver involvement.

Defer preventive treatment in persons with acute hepatic diseases.

How does this medication work? 

Isoniazid inhibits the synthesis of mycoloic acids which is an essential component of the bacterial cell wall. At therapeutic dosages isoniazid is bacteriocidal against both actively growing intracellular and extracellular Mycobacterium tuberculosis organisms.

How should I take this medication? 

Oral: 5-15 mg/kg/dose (usually 300-900mg) at various intervals and durations depending on regimen and patient status.

How to Take: For oral use do not administer with food (bioavailability is decreased). Intramuscular injection may be used for patients who are unable to either take or absorb oral therapy. Inject deep IM into a large muscle mass.  Increase dietary intake of folate, niacin, and magnesium as Isoniazid may decrease folic acid absorption and alters pyridoxine metabolism.

You Need to Avoid:   Avoid tyramine-containing foods (eg, aged or matured cheese, air-dried or cured meats including sausages and salamis; fava or broad bean pods, tap/draft beers, Marmite concentrate, sauerkraut, soy sauce, and other soybean condiments).  Histamine-containing foods (eg, skipjack, tuna, saury, other tropical fish) should also be avoided.

What should I watch for while using this medication? 

Before starting Isoniazid make sure your physician is aware of any allergies or medications you currently take, if you have renal impairment, hepatic impairment, are pregnant, or breastfeeding. Isoniazid use has been associated with rare but serious adverse events such as peripheral neuropathy, and hepatitis.  Isoniazid has weak monoamine oxidase inhibiting activity and may potentially inhibit tyramine metabolism.  Isoniazid may also inhibit diamine oxidase resulting in headache, sweating, palpitations, flushing, diarrhea, itching, wheezing, dyspnea, or hypotension to histamine containing foods.

What if I miss a dose?

If you miss a dose of medication, try to take it as soon as possible. However, if it is almost time for your next dose, take only that scheduled dose. Do not take double or extra doses.

How should I store this medication?

Keep out of the reach of children at all times. Store at room temperature, 59 to 86° F (15 to 30° C). Protect from light. Keep the container tightly closed. Properly dispose of any unused medication after the expiration date.

What are the possible side effects of using this medication?

Increased serum transaminases, vasculitis, brain disease, memory impairment, paresthesia, peripheral neuropathy, psychosis, seizure, skin rash (morbilliform, maculopapular, pruritic, or exfoliative), toxic epidermal necrolysis, gynecomastia, hyperglycemia, metabolic acidosis, pellagra, pyridoxine deficiency, epigastric distress, nausea, pancreatitis, vomiting, bilirubinuria, agranulocytosis, anemia (sideroblastic, hemolytic, or aplastic), eosinophilia, lymphadenopathy, thrombocytopenia, hepatitis, hyperbilirubinemia, jaundice, DRESS syndrome, lupus-like syndrome, rheumatic disease, optic atrophy, optic neuritis, fever.

Note this is not a complete list of side effects for Isoniazid, only common ones.