QUADMAX Rifampicin / Isoniazid / Pyrazinamide / Ethambutol 150mg / 75mg / 400mg / 275mg Film-Coated Tablet 1's
RXDRUG-DRP-703-03-1pc
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RXDRUG-DRP-703-03-1pc
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In stock
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₱1260 |
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Features
Brand
Quadmax
Full Details
Dosage Strength
150 mg / 75 mg / 400 mg / 275 mg
Drug Ingredients
- Ethambutol
- Isoniazid
- Pyrazinamide
- Rifampicin
Drug Packaging
Film-Coated Tablet 1's
Generic Name
Rifampicin / Isoniazid / Pyrazinamide / Ethambutol
Dosage Form
Film-Coated Tablet
Registration Number
DRP-703-03
Drug Classification
Prescription Drug (RX)
Description
Indications/Uses
Treatment of both pulmonary and extrapulmonary tuberculosis in the intensive initial phase of treatment.
Dosage/Direction for Use
Adults: 3 tablets/day for an average body weight of 50 kg.
Patients weighing >70 kg: 5 tablets; 55-70 kg: 4 tablets; 38-54 kg: 3 tablets; 30-37 kg: 2 tablets. All doses to be taken once daily for 2 months on intensive phase.
Patients weighing >70 kg: 5 tablets; 55-70 kg: 4 tablets; 38-54 kg: 3 tablets; 30-37 kg: 2 tablets. All doses to be taken once daily for 2 months on intensive phase.
Administration
Should be taken on an empty stomach: Take at least 30 min before meals.
Contraindications
Hypersensitivity to rifampicin, isoniazid, pyrazinamide or ethambutol.
Isoniazid: Previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid eg, fever, chills and arthritis; acute liver disease of any etiology, a history of previous hypersensitivity reaction to isoniazid including drug-induced hepatitis.
Isoniazid: Previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid eg, fever, chills and arthritis; acute liver disease of any etiology, a history of previous hypersensitivity reaction to isoniazid including drug-induced hepatitis.
Warnings
Ethambutol: Patients with known optic neuritis unless clinical judgement determines that it may be used.
Pyrazinamide: Patients should have baseline serum uric acid and liver function determinations. Patients with preexisting liver disease or those patients at increased risk for drug-related hepatitis (eg, alcohol abusers) should be followed closely. Because it contains pyrazinamide, Quadmax should be discontinued and not be resumed if signs of hepatocellular damage or hyperuricemia accompanied by an acute gouty arthritis appear. If hyperuricemia accompanied by an acute gouty arthritis occurs without liver dysfunction, the patient should be transferred to a regimen not containing pyrazinamide.
Pyrazinamide: Patients should have baseline serum uric acid and liver function determinations. Patients with preexisting liver disease or those patients at increased risk for drug-related hepatitis (eg, alcohol abusers) should be followed closely. Because it contains pyrazinamide, Quadmax should be discontinued and not be resumed if signs of hepatocellular damage or hyperuricemia accompanied by an acute gouty arthritis appear. If hyperuricemia accompanied by an acute gouty arthritis occurs without liver dysfunction, the patient should be transferred to a regimen not containing pyrazinamide.
Special Precautions
Rifampicin: Rifampicin is not recommended for intermittent therapy; the patient should be cautioned against intentional or accidental interruption of the daily dosage regimen since rare renal hypersensitivity reactions have been reported when therapy was resumed in such cases. Rifampicin has been observed to increase the requirements for anticoagulant drugs of the coumarin type. The cause of the phenomenon is unknown. In patients receiving anticoagulants and rifampicin concurrently, it is recommended that the prothrombin time be performed daily or as frequently as necessary to establish and maintain the required dose of anticoagulant. Urine, feces, saliva, sputum, sweat and tears may be colored red-orange by rifampicin and its metabolites. Soft contact lenses may be permanently stained. Individuals to be treated should be made aware of these possibilities.
It has been reported that the reliability of oral contraceptives may be affected in some patients being treated for tuberculosis with rifampicin in combination with at least 1 other antituberculosis drug. In such cases, alternative contraceptive measures may need to be considered. It has also been reported that rifampicin given in combination with other antituberculosis drugs may decrease the pharmacologic activity of methasone, oral hypoglycemics, digitoxin, quinidine, disopyramide, dapsone and corticosteroids. In these cases, dosage adjustment of the interacting drugs is recommended.
Therapeutic levels of rifampicin have been shown to inhibit standard microbiological assays for serum folate and vitamin B12. Alternative methods must be considered when determining folate and vitamin B12 concentrations in the presence of rifampicin.
Isoniazid: All drugs should be stopped and an evaluation of the patient should be made at the first sign of a hypersensitivity reaction. Use of isoniazid should be carefully monitored in the following: Patients who are receiving phenytoin (diphenylhydantoin) concurrently. Isoniazid may decrease the excretion of phenytoin or may enhance its effects. To avoid phenytoin intoxication, appropriate adjustment of the anticonvulsant dose should be made; daily users and ingestion of alcohol may be associated with a higher incidence of isoniazid-hepatitis; patient with current chronic liver disease or severe renal dysfunction. Periodic ophthalmoscopic examination during isoniazid therapy is recommended when visual symptoms occur.
Ethambutol: The effects of combinations of ethambutol with other antituberculous drugs on the fetus is not known. Patients with decreased renal function need the dosage reduced as determined by serum levels of ethambutol, since the main path of excretion of this drug is by the kidneys. Because ethambutol may have adverse effects on vision, physical examination should include ophthalmoscopy, finger perimetry and testing of color discrimination. In patients with visual defects eg, cataracts recurrent inflammatory conditions of the eye, optic neuritis and diabetic retinopathy, the evaluation of changes in visual acuity is more difficult and care should be taken to be sure the variations in vision are not due to the underlying disease conditions. In such patients expected and possible visual deterioration since evaluation of visual changes is difficult. As with any potent drug, periodic assessment of organ system functions, including renal, hepatic and hematopoietic should be made during long-term therapy.
Pyrazinamide: Pyrazinamide inhibits renal excretion of urates, frequently resulting in hyperuricemia which is usually asymptomatic. Pyrazinamide also causes hyperuricemia which is accompanied by acute gouty arthritis.
Use in pregnancy & lactation: Rifampicin: Since rifampicin has been reported to cross the placental barrier and appear in cord blood and in maternal milk, neonates and newborns of rifampicin-treated mothers should be carefully observed for any evidence of untoward effects.
Ethambutol: While administration of ethambutol to pregnant human patients has produced no detectable effect upon the fetus, the possible teratogenic potential in women capable of bearing children would be weighed carefully against the benefits of therapy. There are published reports of 5 women who received ethambutol during pregnancy without apparent adverse effect upon the fetus.
Use in children: Ethambutol is not recommended for use in children <13 years since safe conditions for use have not been established.
It has been reported that the reliability of oral contraceptives may be affected in some patients being treated for tuberculosis with rifampicin in combination with at least 1 other antituberculosis drug. In such cases, alternative contraceptive measures may need to be considered. It has also been reported that rifampicin given in combination with other antituberculosis drugs may decrease the pharmacologic activity of methasone, oral hypoglycemics, digitoxin, quinidine, disopyramide, dapsone and corticosteroids. In these cases, dosage adjustment of the interacting drugs is recommended.
Therapeutic levels of rifampicin have been shown to inhibit standard microbiological assays for serum folate and vitamin B12. Alternative methods must be considered when determining folate and vitamin B12 concentrations in the presence of rifampicin.
Isoniazid: All drugs should be stopped and an evaluation of the patient should be made at the first sign of a hypersensitivity reaction. Use of isoniazid should be carefully monitored in the following: Patients who are receiving phenytoin (diphenylhydantoin) concurrently. Isoniazid may decrease the excretion of phenytoin or may enhance its effects. To avoid phenytoin intoxication, appropriate adjustment of the anticonvulsant dose should be made; daily users and ingestion of alcohol may be associated with a higher incidence of isoniazid-hepatitis; patient with current chronic liver disease or severe renal dysfunction. Periodic ophthalmoscopic examination during isoniazid therapy is recommended when visual symptoms occur.
Ethambutol: The effects of combinations of ethambutol with other antituberculous drugs on the fetus is not known. Patients with decreased renal function need the dosage reduced as determined by serum levels of ethambutol, since the main path of excretion of this drug is by the kidneys. Because ethambutol may have adverse effects on vision, physical examination should include ophthalmoscopy, finger perimetry and testing of color discrimination. In patients with visual defects eg, cataracts recurrent inflammatory conditions of the eye, optic neuritis and diabetic retinopathy, the evaluation of changes in visual acuity is more difficult and care should be taken to be sure the variations in vision are not due to the underlying disease conditions. In such patients expected and possible visual deterioration since evaluation of visual changes is difficult. As with any potent drug, periodic assessment of organ system functions, including renal, hepatic and hematopoietic should be made during long-term therapy.
Pyrazinamide: Pyrazinamide inhibits renal excretion of urates, frequently resulting in hyperuricemia which is usually asymptomatic. Pyrazinamide also causes hyperuricemia which is accompanied by acute gouty arthritis.
Use in pregnancy & lactation: Rifampicin: Since rifampicin has been reported to cross the placental barrier and appear in cord blood and in maternal milk, neonates and newborns of rifampicin-treated mothers should be carefully observed for any evidence of untoward effects.
Ethambutol: While administration of ethambutol to pregnant human patients has produced no detectable effect upon the fetus, the possible teratogenic potential in women capable of bearing children would be weighed carefully against the benefits of therapy. There are published reports of 5 women who received ethambutol during pregnancy without apparent adverse effect upon the fetus.
Use in children: Ethambutol is not recommended for use in children <13 years since safe conditions for use have not been established.
Use In Pregnancy & Lactation
Rifampicin: Since rifampicin has been reported to cross the placental barrier and appear in cord blood and in maternal milk, neonates and newborns of rifampicin-treated mothers should be carefully observed for any evidence of untoward effects.
Ethambutol: While administration of ethambutol to pregnant human patients has produced no detectable effect upon the fetus, the possible teratogenic potential in women capable of bearing children would be weighed carefully against the benefits of therapy. There are published reports of 5 women who received ethambutol during pregnancy without apparent adverse effect upon the fetus.
Ethambutol: While administration of ethambutol to pregnant human patients has produced no detectable effect upon the fetus, the possible teratogenic potential in women capable of bearing children would be weighed carefully against the benefits of therapy. There are published reports of 5 women who received ethambutol during pregnancy without apparent adverse effect upon the fetus.
Adverse Reactions
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.
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.
Drug Interactions
Other anti-TB drugs, methasone, oral hypoglycemics, digitoxin, quinidine, disopyramide, dapsone, corticosteroid. Phenytoin, alcohol.
Storage
Store at temperatures not exceeding 30°C.
Action
Antituberculosis.
Pharmacology: Rifampicin: The oral administration of rifampicin produces peak plasma concentrations in 2-4 hrs. The t½ of rifampicin varies from 1.5-5 hrs and is increased in the presence of hepatic dysfunction; it may be decreased in patients receiving isoniazid concurrently who are slow inactivators of rifampicin. Up to 30% of a dose of rifampicin is excreted in the urine; less than half of this may be unaltered antibiotic. Adjustment of dosage is not necessary in patients with impaired renal function.
Isoniazid: Peak plasma concentrations of 3-5 mcg/mL develop 1-2 hrs after oral ingestion of usual doses. From 75-95% of a dose of isoniazid is excreted in the urine within 24 hrs, as metabolites. The main excretory products in man are the result of enzymatic acetylation (acetylisoniazid) and hydrolysis (isonicotinic acid). The rate of acetylation significantly alters the concentrations of rifampicin that are achieved in plasma and its t½ in the circulation. The t½ of rifampicin may be prolonged in the presence of hepatic insufficiency.
Ethambutol: After oral administration, 75-80% of ethambutol is absorbed from the gastrointestinal tract. A single dose of 15 mg/kg produces a plasma concentration of about 5 mcg/mL at 2-4 hrs. Ethambutol has a t½ of 3-4 hrs. Within 24 hrs, 2/3 of an ingested dose of ethambutol is excreted unchanged in the urine; up to 15% is excreted in the form of 2 metabolites, an aldehyde and a dicarboxylic acid derivative. Renal clearance of ethambutol is approximately 7 mL/min/kg and ethambutol is excreted by tubular secretion in addition to glomerular filtration.
Pyrazinamide: Pyrazinamide is well absorbed from the gastrointestinal tract and attains peak plasma concentrations within 2 hrs. Plasma concentrations generally range from 30-50 mcg/mL with doses of 20-25 mg/kg. It is widely distributed in body tissues and fluids including the liver, lungs and cerebrospinal fluid. It is approximately 10% bound to plasma proteins. The plasma t½ of pyrazinamide is 9-10 hrs in patients with normal renal and hepatic function. The t½ of pyrazinamide may be prolonged in patients with impaired renal or hepatic function. Within 24 hrs, approximately 70% of an oral dose of pyrazinamide is excreted in urine, mainly by glomerular filtration. About 4-14% of the dose is excreted as unchanged drug; the remainder is excreted as metabolites.
Pharmacology: Rifampicin: The oral administration of rifampicin produces peak plasma concentrations in 2-4 hrs. The t½ of rifampicin varies from 1.5-5 hrs and is increased in the presence of hepatic dysfunction; it may be decreased in patients receiving isoniazid concurrently who are slow inactivators of rifampicin. Up to 30% of a dose of rifampicin is excreted in the urine; less than half of this may be unaltered antibiotic. Adjustment of dosage is not necessary in patients with impaired renal function.
Isoniazid: Peak plasma concentrations of 3-5 mcg/mL develop 1-2 hrs after oral ingestion of usual doses. From 75-95% of a dose of isoniazid is excreted in the urine within 24 hrs, as metabolites. The main excretory products in man are the result of enzymatic acetylation (acetylisoniazid) and hydrolysis (isonicotinic acid). The rate of acetylation significantly alters the concentrations of rifampicin that are achieved in plasma and its t½ in the circulation. The t½ of rifampicin may be prolonged in the presence of hepatic insufficiency.
Ethambutol: After oral administration, 75-80% of ethambutol is absorbed from the gastrointestinal tract. A single dose of 15 mg/kg produces a plasma concentration of about 5 mcg/mL at 2-4 hrs. Ethambutol has a t½ of 3-4 hrs. Within 24 hrs, 2/3 of an ingested dose of ethambutol is excreted unchanged in the urine; up to 15% is excreted in the form of 2 metabolites, an aldehyde and a dicarboxylic acid derivative. Renal clearance of ethambutol is approximately 7 mL/min/kg and ethambutol is excreted by tubular secretion in addition to glomerular filtration.
Pyrazinamide: Pyrazinamide is well absorbed from the gastrointestinal tract and attains peak plasma concentrations within 2 hrs. Plasma concentrations generally range from 30-50 mcg/mL with doses of 20-25 mg/kg. It is widely distributed in body tissues and fluids including the liver, lungs and cerebrospinal fluid. It is approximately 10% bound to plasma proteins. The plasma t½ of pyrazinamide is 9-10 hrs in patients with normal renal and hepatic function. The t½ of pyrazinamide may be prolonged in patients with impaired renal or hepatic function. Within 24 hrs, approximately 70% of an oral dose of pyrazinamide is excreted in urine, mainly by glomerular filtration. About 4-14% of the dose is excreted as unchanged drug; the remainder is excreted as metabolites.
MedsGo Class
Anti-TB Agents
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