MYCOBUTIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYCOBUTIN (MYCOBUTIN).
Inhibits DNA-dependent RNA polymerase in Mycobacterium tuberculosis, blocking RNA synthesis.
| Metabolism | Hepatic via deacetylation; CYP3A4 substrate |
| Excretion | Renal (30% as unchanged drug), fecal (50-60% as metabolites and parent compound), biliary (minor). |
| Half-life | Terminal elimination half-life: 35-40 hours (range 30-50 hours). Clinical context: Allows once-daily dosing; prolonged in hepatic or renal impairment. |
| Protein binding | ~71-85% (primarily to albumin). |
| Volume of Distribution | Vd: 8-10 L/kg. Clinical meaning: Extensive tissue penetration; concentration in macrophages is 10-20 times plasma levels. |
| Bioavailability | Oral: 85-95% (well absorbed; food may reduce rate but not extent). |
| Onset of Action | Oral: 2-4 hours for time to peak concentration; clinical effect (e.g., reduction of Mycobacterium avium complex bacteremia) typically observed within 2-4 weeks. |
| Duration of Action | Duration of action: ~24 hours based on once-daily dosing regimen. Clinical notes: Intracellular killing persists beyond plasma elimination due to extensive tissue distribution. |
300 mg orally once daily, or 300 mg twice weekly for MAC prophylaxis in HIV. For TB, 300 mg daily as part of combination therapy.
| Dosage form | CAPSULE |
| Renal impairment | CrCl <30 mL/min: reduce dose to 150 mg daily or 300 mg twice weekly. No adjustment for CrCl >30 mL/min. |
| Liver impairment | Child-Pugh B or C: contraindicado. Child-Pugh A: no specific dose adjustment, but monitor LFTs. |
| Pediatric use | 5-10 mg/kg orally once daily (max 300 mg). For MAC prophylaxis: based on age/weight, typically 5 mg/kg daily. |
| Geriatric use | Use with caution due to age-related renal decline; start at lower end of dosing (150 mg daily) if renal impairment present. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MYCOBUTIN (MYCOBUTIN).
| Breastfeeding | Limited data: rifabutin is excreted into human breast milk; the M/P ratio is not well established. Because of the potential for adverse effects in nursing infants (e.g., rash, gastrointestinal disturbances), caution is advised. The benefits of breastfeeding should be weighed against the risks. |
| Teratogenic Risk | Mycobutin (rifabutin) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects, but there are no adequate and well-controlled studies in pregnant women. First trimester exposure: theoretical risk based on animal studies, but no human data suggest increased malformations. Second and third trimesters: no known fetal toxicity; however, rifabutin may cause maternal vitamin K deficiency leading to neonatal hemorrhage if used near term. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to rifabutin or any rifamycin","Concomitant use with delavirdine (significant decrease in delavirdine levels)"]
| Precautions | ["Hepatotoxicity: Monitor liver function tests","Peripheral neuropathy: May occur, especially at higher doses","Ocular toxicity: Dosage-related; reversible with discontinuation","Drug interactions: Induces CYP3A4; decreases levels of drugs metabolized by CYP3A4 (e.g., protease inhibitors, oral contraceptives)","Rash and gastrointestinal intolerance"] |
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| Fetal Monitoring | Monitor maternal hepatic function, CBC with platelets, and signs of uveitis. In fetus, monitor for growth restriction and signs of hemolytic anemia. Consider neonatal monitoring for hyperbilirubinemia and vitamin K deficiency if used near term. |
| Fertility Effects | No known adverse effects on fertility in human studies. Animal studies have not shown impairment of fertility. |