Butalbital, acetaminophen, caffeine, and codeine and Isoniazid interaction

Interactions with Drugs Affecting Cytochrome P450 Isoenzymes The effects of concomitant use or discontinuation of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with codeine are complex.

Use of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with Butalbital, Acetaminophen, Caffeine, and Codeine Phosphate Capsules requires careful consideration of the effects on codeine, and the active metabolite, morphine [see Warnings and Precautions ( 5.7 )] .

• The effects of concomitant use or discontinuation of cytochrome P450 3A4 inducers, 3A4 inhibitors, or 2D6 inhibitors with codeine are complex.

…Precautions ( 5.2 )] • Acute or severe bronchial asthma in an unmonitored setting or in the absence of resuscitative equipment [see Warnings and Precautions ( 5.10 )] • Concurrent use of monoamine oxidase inhibitors (MAOIs) or use of MAOIs within the last 14 days [see Warnings and Precautions ( 5.11 ), Drug Interactions ( 7 )] • Known or suspected gastrointestinal obstruction,…

• Concurrent use of monoamine oxidase inhibitors (MAOIs) or use of MAOIs within the last 14 days.

Acetaminophen A report of severe acetaminophen toxicity was reported in a patient receiving isoniazid.

It is believed that the toxicity may have resulted from a previously unrecognized interaction between isoniazid and acetaminophen and a molecular basis for this interaction has been proposed.

Studies have demonstrated that pretreatment with isoniazid potentiates acetaminophen hepatotoxicity in rats 1,2 .

Theophylline A recent study has shown that concomitant administration of isoniazid and theophylline may cause elevated plasma levels of theophylline, and in some instances a slight decrease in the elimination of isoniazid.

Since the therapeutic range of theophylline is narrow, theophylline serum levels should be monitored closely, and appropriate dosage adjustments of theophylline should be made 7 .