Isoniazid Side Effects

Please note - some side effects for Isoniazid may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA at http://www.fda.gov/medwatch/ or 1-800-FDA-1088 (1-800-332-1088).

Side Effects of Isoniazid - for the Consumer

Isoniazid/Rifampin

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Isoniazid/Rifampin:

Diarrhea; dizziness; drowsiness; gas; headache; heartburn; mild stomach upset or cramps; nausea; trouble sleeping.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bloody stools; change in the amount of urine produced; changes in vision; chills or fever; dark urine; general feeling of discomfort; increased thirst or urination; joint pain or swelling; loss of appetite; memory problems; menstrual changes; mental or mood changes; seizures; severe diarrhea, nausea, or stomach cramps; shortness of breath; stomach pain or tenderness; swelling of the hands or legs; symptoms of low vitamin B₆ levels (eg, confusion, cracks in the corners of the mouth, irritability, mouth redness or soreness, scaly rash); tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

Isoniazid

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Isoniazid:

Mild stomach upset.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); changes in vision; chills or fever; dark urine; general feeling of discomfort; increased thirst or urination; joint pain or swelling; loss of appetite; memory problems; mental or mood changes; nausea; seizures; stomach pain or tenderness; symptoms of low vitamin B₆ levels (eg, confusion, cracks in the corners of the mouth, irritability, mouth redness or soreness, scaly rash); tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

Isoniazid/Pyrazinamide/Rifampin

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Isoniazid/Pyrazinamide/Rifampin:

Diarrhea; dizziness; drowsiness; gas; headache; heartburn; mild joint or muscle aches; mild stomach upset or cramps; nausea; trouble sleeping.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); bloody stools; change in the amount of urine produced; changes in vision; chest pain; coughing up blood; dark urine; fever, chills, or sore throat; general feeling of discomfort; increased thirst or urination; irregular heartbeat; joint pain or swelling; loss of appetite; memory problems; menstrual changes; mental or mood changes; nausea; ringing in the ears; seizures; severe diarrhea, nausea, or stomach cramps; severe or persistent muscle pain; severe pain or tenderness in the big toe; shortness of breath; stomach pain or tenderness; swelling of the hands or legs; swollen lymph nodes; symptoms of low B₆ levels (eg, confusion, cracks in the corners of the mouth, irritability, mouth redness or soreness, scaly rash); tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

Isoniazid Syrup

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Isoniazid Syrup:

Mild stomach upset.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); changes in vision; chills or fever; dark urine; general feeling of discomfort; increased thirst or urination; joint pain or swelling; loss of appetite; memory problems; mental or mood changes; nausea; seizures; stomach pain or tenderness; symptoms of low vitamin B₆ levels (eg, confusion, cracks in the corners of the mouth, irritability, mouth redness or soreness, scaly rash); tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

Isoniazid Tablets

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Isoniazid Tablets:

Mild stomach upset.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); changes in vision; chills or fever; dark urine; general feeling of discomfort; increased thirst or urination; joint pain or swelling; loss of appetite; memory problems; mental or mood changes; nausea; seizures; stomach pain or tenderness; symptoms of low vitamin B₆ levels (eg, confusion, cracks in the corners of the mouth, irritability, mouth redness or soreness, scaly rash); tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

Isoniazid Side Effects - for the Professional

Isoniazid Injection

The most frequent reactions are those affecting the nervous system and the liver.

Nervous system: Peripheral neuropathy is the most common toxic effect. It is dose related, occurs most often in the malnourished and in those predisposed to neuritis (e.g., alcoholics and diabetics), and is usually preceded by paresthesias of the feet and hands. The incidence is higher in "slow acetylators."

Other neurotoxic effects which are uncommon with conventional doses are convulsions, toxic encephalopathy, optic neuritis and atrophy, memory impairment, and toxic psychosis.

Gastrointestinal: Nausea, vomiting, and epigastric distress.

Hepatic: See boxed WARNING. Elevated serum transaminases (SGOT; SGPT), bilirubinemia, bilirubinuria, jaundice, and occasionally severe and sometimes fatal hepatitis. The common prodromal symptoms of hepatitis are anorexia, nausea, vomiting, fatigue, malaise, and weakness. Mild hepatic dysfunction, evidenced by mild and transient elevation of serum transaminase levels occurs in 10 to 20 percent of patients taking Isoniazid. This abnormality usually appears in the first 1 to 3 months of treatment but can occur at any time during therapy. In most instances, enzyme levels return to normal, and generally, there is no necessity to discontinue medication during the period of mild serum transaminase elevation. In occasional instances, progressive liver damage occurs, with accompanying symptoms. If the SGOT value exceeds three to five times the upper limit of normal, discontinuation of the Isoniazid should be strongly considered. The frequency of progressive liver damage increases with age. It is rare in persons under 20, but occurs in up to 2.3 percent of those over 50 years of age.

Hematologic: Agranulocytosis; hemolytic, sideroblastic, or aplastic anemia; thrombocytopenia; and eosinophilia.

Hypersensitivity: Fever, skin eruptions (morbilliform, maculopapular, purpuric, or exfoliative), lymphadenopathy, and vasculitis.

Metabolic and endocrine: Pyridoxine deficiency, pellagra, hyperglycemia, metabolic acidosis, and gynecomastia.

Miscellaneous: Rheumatic syndrome and systemic lupus erythematosus-like syndrome. Local irritation has been observed at the site of intramuscular injection.

Side Effects by Body System

Nervous system

Overdose of isoniazid has been associated with uncontrollable seizures. Dialysis may be required to decrease isoniazid blood levels, thereby controlling seizures. Seizures, lethargy, and confusion have also been reported in patients with chronic renal failure. Other patients at risk for neurotoxicity include the malnourished and alcoholics. Optic neuritis has also been reported in patients on hemodialysis.

Peripheral neuropathy has been observed and occurs frequently, especially at doses greater than 300 mg daily. Neuropathy may be prevented or attenuated by coadministration of pyridoxine 50 to 100 mg daily. Other neurologic reactions, although rare, have included visual disturbances, ataxia, and seizures.

Hepatic

Hepatitis has been reported in less than 5% of patients receiving isoniazid alone. Jaundice is usually preceded by a prodromal illness with fatigue, nausea, malaise, abdominal pain, and anorexia. Asymptomatic increases in liver function tests may occur. Isoniazid should be discontinued if hepatotoxicity occurs, usually defined as SGOT greater than four times normal.

The mechanism of hepatic injury is unknown but may be related to the acetyl metabolite of isoniazid. Patients exhibiting hepatotoxicity are more likely to be fast acetylators of isoniazid. Eight cases of severe hepatitis resulting in death or transplantation have been evaluated by the Department of Health of New York. Duration of isoniazid use before onset of hepatitis ranged from 21 to 142 days, and seven patients continued use of isoniazid at least 10 days after onset of symptoms. Massive hepatic necrosis was a common finding and cholestasis was present in two of five cases.

The risk is age related with a greater occurrence reported in patients who are 35 years or older. The risk of hepatitis is also increased in patients who consume alcohol daily, in women, and in minorities. In a study of 2651 women beginning isoniazid preventive therapy during pregnancy or postpartum, 5 cases of isoniazid-induced hepatitis were identified, including two fatalities. In another review of deaths due to isoniazid, eight of 21 women between 15 and 44 years old were within one year postpartum. In general, death due to isoniazid hepatotoxicity occurs more frequently in women than men.

Fulminate hepatitis, characterized by jaundice, disorders of consciousness and elevated serum transaminases up to 80 times the upper limit of normal, has occasionally occurred in patients receiving isoniazid with rifampin. Rifampin, by virtue of its enzyme-inducing activity, likely increases the reactive metabolite of isoniazid thought to be responsible for the hepatotoxicity associated with isoniazid.

Monthly monitoring and interviewing of patients should take place. Patients should be fully informed regarding the risk of hepatotoxicity associated with isoniazid, educated about the signs and symptoms of liver damage, and instructed to contact their physician immediately if they develop signs or symptoms.

Hematologic

Several cases have been reported of pure red cell aplasia attributable to isoniazid. Abnormalities resolved following drug discontinuation.

Hematologic abnormalities such as anemia have been reported. Anemia is generally reversible following discontinuation of isoniazid. Agranulocytosis, thrombocytopenia, and eosinophilia have rarely been reported.

Hypersensitivity

Hypersensitivity reactions including drug fever, rash, lymphadenopathy, vasculitis, and urticaria have been reported but are rare. These reactions generally subside following drug discontinuation.

Immunologic

Isoniazid-induced lupus-like reactions have been reported with an incidence of approximately 1%. However, as many as 22% of patients on this drug may develop positive antinuclear antibodies. Drug discontinuation is recommended if a lupus-like reaction occurs.

Psychiatric

Psychosis, depression, and aggression have been rarely reported with isoniazid therapy. Some patients with preexisting schizophrenia have experienced exacerbations when isoniazid was started.

Gastrointestinal

Gastrointestinal adverse effects have included nausea, vomiting, and epigastric distress. A few cases of pancreatitis have been reported.

Metabolic

Metabolic side effects such as pyridoxine deficiency and pellagra have been reported. Isoniazid induced hypocalcemia and hypophosphatemia has been observed and may be due to altered vitamin D metabolism.

Local

Local irritation has been observed at the site of intramuscular injection of isoniazid.

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