Rifampicin: Nervous System Reactions: Headache, drowsiness, fatigue, ataxia, dizziness, inability to concentrate, mental confusion, visual disturbances, muscular weakness, pain in extremities and generalized numbness.
Gastrointestinal Disturbances: In some patients, heartburn, epigastric distress, anorexia, nausea, vomiting, gas, cramps and diarrhea.
Hepatic Reactions: Transient abnormalities in liver function tests (eg, elevations in serum bilirubin, bromsulphalein (BSP), alkaline phosphatase, serum transaminases) have been observed. Rarely, hepatitis or a shock-like syndrome with hepatic involvement and abnormal liver function tests.
Renal Reactions: Elevations in blood urea nitrogen (BUN) and serum uric acid have been reported. Rarely, hemolysis, hemoglobinuria, hematuria, interstitial nephritis, renal insufficiency and acute renal failure have been noted. These are generally considered to be hypersensitivity reactions. They usually occur during intermittent therapy or when treatment is resumed following intentional or accidental interruption of a daily dosage regimen, and are reversible when rifampicin is discontinued and appropriate therapy instituted.
Hematologic Reactions: Thrombocytopenia, transient leukopenia, hemolytic anemia, eosinophilia and decreased hemoglobin have been observed. Thrombocytopenia has occurred when rifampicin and ethambutol were administered concomitantly according to an intermittent dose schedule twice weekly and in high doses.
Allergic and Immunological Reactions: Occasionally, pruritus, urticaria, rash, pemphigoid reaction, eosinophilia, sore mouth, sore tongue and exudative conjunctivitis. Rarely, hemolysis, hemoglobinuria, hematuria, renal insufficiency or acute renal failure have been reported which are generally considered to be hypersensitivity reactions. These have usually occurred during intermittent therapy or when treatment was resumed following intentional or accidental interruption of a daily dosage regimen, and were reversible when rifampicin was discontinued and appropriate therapy instituted.
Metabolic Reactions: Elevations in BUN and serum uric acid have occurred.
Miscellaneous Reactions: Fever and menstrual disturbances have been noted.
Isoniazid: Nervous System Reactions: Peripheral neuropathy is the most common toxic effect. It is dose-related, occurs most often in the malnourished and in those predisposed to neuritis (eg, alcoholics and diabetics), and is usually preceded by paresthesias of the feet and hands. The incidence is higher in slow inactivators. Other neurotoxic effects, which are uncommon with conventional doses, are convulsions, toxic encephalopathy, optic neuritis and atrophy, memory impairment and toxic psychosis.
Gastrointestinal Reactions: Nausea, vomiting and epigastric distress.
Hepatic Reactions: Elevated serum transaminases [serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT)], bilirubinemia, bilirubinuria, jaundice and occasionally, severe and sometimes fatal hepatitis. The common prodromal symptoms are anorexia, nausea, vomiting, fatigue, malaise and weaknesses. Mild and transient elevations of serum transaminase levels occur in 10 to 2% of persons taking isoniazid. The abnormality usually occurs in the first 4-6 months of treatment but can occur at any time during therapy. In most instances, enzyme levels return to normal with no necessity to discontinue medication. In occasional instances, progressive liver damage occurs, with accompanying symptoms. In these cases, Quadmax should be discontinued immediately. The frequency of progressive liver damage increases with age. It is rare in patients <20 years, but occurs in up to 2.3% of those >50 years.
Hematologic Reactions: Agranulocytosis, hemolytic sideroblastic or aplastic anemia, thrombocytopenia and eosinophilia.
Hypersensitivity Reactions: Fever, skin eruptions (morbilliform, maculopapular, purpuric or exfoliative), lymphadenopathy and vasculitis.
Metabolic and Endocrine Reactions: Pyridoxine deficiency, pellagra, hyperglycemia, metabolic acidosis and gynecomastia.
Miscellaneous Reactions: Rheumatic syndrome and systemic lupus erythematosus-like syndrome.
Ethambutol: Ethambutol may produce decreases in visual acuity which appear to be due to optic neuritis and to be related to dose and duration of treatment. The effects are generally reversible when administration of ethambutol is discontinued promptly. In rare cases, recovery may be delayed for up to ≥1 year and the effect may possibly be irreversible in these cases. The change in visual acuity may be unilateral or bilateral and hence, each eye must be tested separately and both eyes tested together. Testing of visual acuity should be performed before beginning ethambutol therapy and periodically during drug administration, except that it should be done monthly when a patient is on a dosage of >15 mg/kg/day. If careful evaluation confirms the magnitude of visual change and fails to reveal another cause, ethambutol should be discontinued and the patient re-evaluated at frequent intervals. Progressive decreases in visual acuity during therapy must be considered to be due ethambutol HCl.
Ethambutol may show subjective visual symptoms before, or simultaneously with, the demonstration of decreases in visual acuity, and all patients receiving ethambutol should be questioned periodically about blurred vision and other subjective eye symptoms. Other adverse reactions reported include: Anaphylactoid reactions, dermatitis, pruritus and joint pain; anorexia, nausea, vomiting, gastrointestinal upset, abdominal pain; fever, malaise, headache and dizziness; mental confusion, disorientation and possible hallucinations. Numbness and tingling of the extremities due to peripheral neuritis have been reported infrequently. Elevated serum uric acid levels occurs and precipitation of acute gout has been reported. Transient impairment of liver function as indicated by abnormal liver function tests is not an unusual finding. Since ethambutol is recommended for therapy in conjunction with ≥1 other antituberculous drugs, these changes may be related to the concurrent therapy.
Pyrazinamide: Flushing is quite common and hypersensitivity reactions and photosensitization rarely occur. Mild degrees of anorexia and nausea are common, but vomiting is less frequent. Clinically, the 2 most important reactions are hepatitis and arthralgia. The frequency of hepatotoxicity declines with reduction of dosage even in combination with isoniazid or rifampicin. Inhibition of the renal tubular secretion of uric acid by pyrazinoic acid, the main metabolite of the drug, increases the serum uric acid concentration and may precipitate an acute attack in patients with gout. Hyperuricemia is reduced by co-administration of rifampicin, evidently by facilitation of uric acid excretion rather than any effect on metabolism. Sideroblastic anemia is a rare, reversible reaction. Convulsions have been described.