Mycobutin (Rifabutin) - Drug Interactions, Contraindications, Overdosage, etc

DRUG INTERACTIONS

Effects on Other Drugs

Rifabutin induces CYP3A enzymes and therefore may reduce the plasma concentrations of drugs metabolized by those enzymes. This effect may reduce the efficacy of standard doses of such drugs, which include itraconazole, clarithromycin, and saquinavir (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions).

Effects on Rifabutin

Some drugs that inhibit CYP3A may significantly increase the plasma concentration of rifabutin. Because high plasma levels of rifabutin may increase the risk of adverse reactions, carefully monitor patients receiving coadministration of such drugs, which include fluconazole and clarithromycin (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions). In some cases, the dosage of MYCOBUTIN may need to be reduced when it is coadministered with such a drug (see below).

Antiretrovirals

Delavirdine

Coadministration of rifabutin and delavirdine is not recommended because rifabutin substantially decreases the plasma concentrations of delavirdine, and delavirdine increases the plasma concentrations of rifabutin (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions).

Indinavir

Coadministration of indinavir and rifabutin increases the plasma concentration of rifabutin. In patients receiving coadministration of indinavir, reduce the dosage of MYCOBUTIN by half (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions).

Nelfinavir

Coadministration of nelfinavir increases the plasma concentration of rifabutin. In patients receiving nelfinavir, reduce the dosage of MYCOBUTIN by half (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions).

Ritonavir

Coadministration of ritonavir is not recommended because it substantially increases the plasma concentration of rifabutin (see CLINICAL PHARMACOLOGY-Drug-Drug Interactions). High plasma concentrations of rifabutin may increase the risk of adverse reactions, including uveitis.

OVERDOSAGE

No information is available on accidental overdosage in humans.

Treatment

While there is no experience in the treatment of overdose with MYCOBUTIN Capsules, clinical experience with rifamycins suggests that gastric lavage to evacuate gastric contents (within a few hours of overdose), followed by instillation of an activated charcoal slurry into the stomach, may help absorb any remaining drug from the gastrointestinal tract.

Rifabutin is 85% protein bound and distributed extensively into tissues (Vss:8 to 9 L/kg). It is not primarily excreted via the urinary route (less than 10% as unchanged drug), therefore, neither hemodialysis nor forced diuresis is expected to enhance the systemic elimination of unchanged rifabutin from the body in a patient with an overdose of MYCOBUTIN.

CONTRAINDICATIONS

MYCOBUTIN Capsules are contraindicated in patients who have had clinically significant hypersensitivity to rifabutin or to any other rifamycins.