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| Interactions: | Antacids Comb. Adverse Effect: Decreased isoniazid effectiveness Clinical Management: Do not administer antacids concurrently with isoniazid. Recommend taking antacids at least two hours after taking isoniazid.
Carbamazepine Adverse Effect: Elevated carbamazepine levels and toxicity (ataxia, nystagmus, diplopia, headache, vomiting, apnea, seizures, coma)
Clinical Management: Watch for signs of carbamazepine toxicity such as nausea, vomiting, drowsiness and ataxia, and consider monitoring serum carbamazepine levels following the addition of isoniazid; lower carbamazepine doses are often required. Conversely, if isoniazid is discontinued or the dosage reduced, carbamazepine levels should be monitored with the dose adjusted accordingly. Usual anticonvulsant levels are 6-12 mg/L.
Cycloserine Adverse Effect: an increased risk of central nervous system toxicity (dizziness, drowsiness) Clinical Management: Monitor patients receiving both cycloserine and isoniazid closely for central nervous system toxicity (dizziness, drowsiness). Dosage adjustments may be necessary.
Diazepam Adverse Effect: an increased risk of Diazepam toxicity (sedation, respiratory depression) Clinical Management: Monitor patients receiving isoniazid and diazepam for signs of Diazepam toxicity, including respiratory depression, somnolence, and sedation.
Disulfiram Adverse Effect: changes in behavior, coordination
Clinical Management: Monitor patients for coordination difficulties and mood or behavioral changes. Consider dose reduction or discontinuation of disulfiram.
Ethionamide Adverse Effect: peripheral neuritis, hepatotoxicity, and encephalopathy
Clinical Management: If possible, avoid concurrent administration of isoniazid and ethionamide in patients with a history of or predisposed to peripheral neuropathy or liver disorders. Patients should be found to have normal baseline liver function before combined isoniazid-ethionamide therapy is initiated. Regular liver function tests should be performed.
Itraconazole Adverse Effect: Loss of itraconazole efficacy
Clinical Management: Monitor itraconazole effectiveness and adjust the dose as needed; larger itraconazole doses may be required in some situations.
KetoconazoleAdverse Effect: increased or decreased levels of ketoconazole
Clinical Management: Dosage adjustments of ketoconazole may be necessary if given concurrently with isoniazid.
Levodopa Adverse Effect: symptomatic deterioration of Parkinsons disease
Clinical Management: Upward titration of antiparkinson drugs may restore response. Monitor patient for clinical response to dosage adjustment and for adverse effects associated with the antiparkinson therapy.
ParacetamolAdverse Effect: An increased risk of hepatotoxicity
Clinical Management: Acetaminophen use should be limited in patients taking isoniazid.
Pethidine Adverse Effect: hypotension and central nervous system depression
Clinical Management: Avoid the concurrent use of Pethidine and isoniazid. If these two agents must be used together, monitor the patient for blood pressure control and excessive central nervous system depression.
PhenytoinAdverse Effect: An increased risk of phenytoin toxicity (ataxia, hyperreflexia, nystagmus, tremor) Clinical Management: Phenytoin levels should be monitored following the addition or discontinuation of isoniazid therapy, and dosage adjustments made accordingly. Usual therapeutic levels are 10-20 mg/L. Patients should be counseled on the potential for phenytoin side effects such as drowsiness, ataxia, and nystagmus, and instructed to report the occurrence of these effects to their clinician right away.
Prednisolone Adverse Effect: Decreased isoniazid effectiveness
Clinical Management: Monitor patients for a decreased response to isoniazid. Dosage adjustments of one or both drugs may be necessary.
Rifampicin Adverse Effect: hepatotoxicity
Clinical Management: For patients on concurrent isoniazid and rifampin, monitor liver function tests, especially in children and in adults with predisposing risk factors. Monitor the patient for clinical symptoms of liver toxicity.
Sodium Valproate Adverse Effect: Valproic acid or isoniazid toxicity
Clinical Management: Consider monitoring liver function tests periodically with therapy, as well as continued assessment of therapeutic efficacy of valproic acid. Monitor serum valproic acid trough concentrations as indicated. If toxicity occurs, an alternative anticonvulsant may be appropriate.
Theophylline Adverse Effect: Theophylline toxicity (nausea, vomiting, palpitations, seizures)
Clinical Management: Theophylline levels should be closely monitored when isoniazid therapy is initiated, changed or discontinued.
WarfarinAdverse Effect: an increased risk of bleeding
Clinical Management: In patients on warfarin therapy, the prothrombin time ratio or INR (international normalized ratio) should be closely monitored with the addition and withdrawal of treatment with isoniazid, and should be reassessed periodically during concurrent therapy. |
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