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Isoniazid / Rifampin Dosage

Applies to the following strength(s): 150 mg-300 mg

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Usual Adult Dose for:

Additional dosage information:

Usual Adult Dose for Tuberculosis - Active

2 capsules (300 mg isoniazid and 600 mg rifampin total dose) orally once a day administered 1 hour before or 2 hours after a meal
Duration: In general, treatment should continue until bacterial conversion and maximal improvement occur.

Renal Dose Adjustments

Data not available

Liver Dose Adjustments

Isoniazid-rifampin is contraindicated in patients with acute liver disease, regardless of etiology.

Precautions

Severe and sometimes fatal hepatitis associated with isoniazid therapy may occur or develop after months of treatment. 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. Monthly monitoring and interviewing of patients should take place. Baseline laboratory values should be obtained in patients over 35 years of age and in patients with a history of liver illness or heavy alcohol consumption. Elevated liver function tests per se are not a contraindication to the use of isoniazid unless they indicate worsening or acute liver disease. Strict monitoring of these patients, however, is crucial. Patients should be fully informed regarding the risk of hepatotoxicity associated with isoniazid, educated about the prodromal symptoms of hepatitis (such as anorexia, nausea, vomiting, fatigue, weakness, or malaise), and instructed to contact their physician immediately if they develop signs or symptoms. Isoniazid should be discontinued at once if these symptoms occur or signs indicative of liver damage are detected; continued use of isoniazid in such cases has been reported to cause a more severe form of liver damage.

Patients with tuberculosis who have hepatitis attributed to isoniazid should be administered appropriate treatment with alternative drugs. If isoniazid must be reinstated, it should be reinstituted only after symptoms and laboratory abnormalities have resolved. Isoniazid should be restarted in very small and gradually increasing doses and should be withdrawn immediately if there is any indication of recurrent liver involvement. Therapy should be deferred in persons with acute hepatic diseases.

Isoniazid-rifampin is contraindicated in patients with previous hepatic injury or severe adverse reactions (such as drug fever, chills, and arthritis) associated with isoniazid. Isoniazid-rifampin is also contraindicated in patients with history of drug-induced hepatitis.

Each component of isoniazid-rifampin has been associated with hepatic dysfunction. Liver function tests should be performed prior to and periodically throughout isoniazid-rifampin therapy.

Rifampin has been shown to produce hepatotoxicity in patients with preexisting liver dysfunction and in patients with normal liver function who are also taking other hepatotoxic agents. Some cases have been fatal. Patients with impaired liver function should only be given isoniazid-rifampin in cases of necessity and then with caution and under strict medical supervision. Careful monitoring of liver function (especially SGPT and SGOT) should be done prior to and then every 2 to 4 weeks throughout treatment in patients with liver dysfunction. Isoniazid-rifampin should be discontinued if signs of hepatocellular damage occur.

Liver function tests and a complete blood count should be performed prior to and periodically throughout isoniazid-rifampin therapy. Blood for baseline clinical chemistries should be obtained prior to isoniazid-rifampin administration due to possible transient transaminase and bilirubin elevations.

In some cases, hyperbilirubinemia has been observed in the early days of rifampin treatment. An isolated report showing a moderate rise in bilirubin and/or transaminase level is not in itself an indication for interrupting therapy; rather, the decision should be made after repeating the laboratory tests, noting trends in the levels, and considering them in conjunction with the patient's clinical condition.

Rifampin is not recommended for intermittent treatment. Rare renal hypersensitivity reactions have been reported in patients resuming treatment following intentional or accidental interruption of the daily regimen.

Isoniazid use should be carefully monitored in patients with the following: severe renal dysfunction, chronic liver disease, concurrent use of any chronically administered medication, or daily ingestion of alcohol.

Because of the numerous drug interactions which may occur with rifampin therapy, the usefulness and effectiveness of all medications in a patient's drug regimen should be evaluated when rifampin is added to or deleted from that regimen.

Isoniazid exhibits some monoamine oxidase inhibiting activity; therefore, an interaction with foods containing tyramine (such as cheese, red wine) may occur. Diamine oxidase may also be inhibited and may cause an exaggerated response (e.g., headache, sweating, palpitations, flushing, hypotension) to histamine-containing foods (including skipjack, tuna, other tropical fish). Patients receiving isoniazid-rifampin should avoid tyramine- and histamine-containing foods.

Ophthalmoscopic examinations are recommended periodically during isoniazid treatment when visual symptoms occur.

In the treatment of tuberculosis, small numbers of resistant cells, present within large populations of susceptible cells, can quickly become the predominating type. Since resistance can occur rapidly, culture and susceptibility tests should be performed if positive cultures persist during the course of treatment.

Safety and effectiveness have not been established in pediatric patients (less than 18 years of age).

Dialysis

Data not available

Other Comments

Pyridoxine, 50 mg orally once a day, may be administered concurrently to prevent the occurrence of peripheral neuropathy caused by the isoniazid component. Concomitant pyridoxine is recommended in malnourished patients, patients predisposed to neuropathy (such as diabetics), and adolescents.

Isoniazid-rifampin should only be used in patients previously titrated on the individual components and in which the therapeutic effectiveness of the fixed dosage has been confirmed.

This combination product should not be used for the initial treatment of tuberculosis. It should only be used after the recommended initial 2 month therapy with isoniazid plus rifampin plus pyrazinamide. The isoniazid-rifampin fixed-dosage combination is not recommended for preventive therapy and it is not indicated for the treatment of meningococcal infections or to eliminate meningococci from the nasopharynx in asymptomatic carriers of Neisseria meningitidis.

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