Rifabutin Flashcards
How does rifabutin’s mechanism of action compare to rifampin’s?
Rifabutin has the same mechanism as rifampin: it inhibits DNA-dependent RNA polymerase in bacteria, thus blocking RNA transcription (bactericidal).
Why might rifabutin be chosen over rifampin in certain patients?
Rifabutin is often chosen in HIV-positive patients with tuberculosis because it is a less potent inducer of cytochrome P450. This results in fewer drug interactions with antiretroviral therapy. It’s also used for prophylaxis of Mycobacterium avium complex (MAC) in AIDS patients (CD4 < 50).
Describe key differences in spectrum or uses between rifabutin and rifampin.
Spectrum is similar (both cover Mycobacteria and some Gram-positives/Gram-negatives). Rifabutin is primarily used for Mycobacterium avium-intracellulare (MAC) prophylaxis and treatment, and as an alternative to rifampin in TB therapy for patients on complex drug regimens (like HIV meds). It can also be used in atypical mycobacterial infections. Rifampin is more commonly used for TB and meningococcal/Hib prophylaxis; rifabutin mostly in HIV/MAC context.
What are notable adverse effects of rifabutin?
Rifabutin shares rifampin’s side effects like orange discoloration of body fluids and hepatotoxicity (still monitor LFTs). Unique or more common to rifabutin are uveitis, polyarthralgias, and leukopenia, especially at higher doses or when combined with clarithromycin (which increases rifabutin levels). It can also cause rash and GI disturbances. Overall, it is usually well tolerated.
How do rifabutin’s drug interactions compare with rifampin’s?
Rifabutin is a cytochrome P450 inducer but to a lesser extent than rifampin. It still can lower levels of certain drugs (e.g., some protease inhibitors and NNRTIs, though less dramatically). Dose adjustments of antiretrovirals may still be needed, but rifabutin makes co-administration more feasible. If rifabutin is given with protease inhibitors, sometimes the rifabutin dose is reduced.
Are there any contraindications specific to rifabutin?
Generally the same cautions as rifampin: caution in patients with active liver disease and in those on interacting drugs (though it’s friendlier for HIV regimens). Avoid in patients with rifamycin hypersensitivity. If a patient had severe rifampin-induced adverse effects, rifabutin might cross-react (since they’re both rifamycins). Check for uveitis symptoms if patient is also on clarithromycin or high dose.
What is a high-yield point for rifabutin for USMLE?
Remember that rifabutin is used in TB treatment for HIV patients due to fewer drug interactions (less P450 induction). Also recall its role in MAC prophylaxis in AIDS. It shares the orange secretions effect. In short: Rifabutin = ‘rifampin for HIV patients’.
