antibioticsbooks

154 PART 3 Antimycobacterial Drugs
Spectrum
Good: most mycobacteria
Moderate: Staphylococcus, Acinetobacter, Enterobacteriaceae
Poor: “typical” bacteria as monotherapy, some
very rare mycobacteria
Adverse Effects
Rifamycins are generally well-tolerated drugs
that are most notorious for their potent CYP450-
inducing effects. Their potent induction of metabolism
can lead to subtherapeutic concentrations of
other drugs that can manifest with devastating
clinical consequences, such as loss of seizure control
(anticonvulsants) or organ rejection (antirejection
agents). Rifampin characteristically colors
secretions (urine, tears, etc.) orange-red and can
actually stain contact lenses, which should not
be worn during rifampin therapy. Otherwise, this
effect is nonpermanent and not harmful, which
patients appreciate knowing. Rifamycins can also
cause hepatotoxicity. Less serious side effects
include rash, nausea, vomiting, and hypersensitivity
(often fever).
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Important Facts
• Rifampin is a drug of choice for tuberculosis,
while rifabutin is a drug of choice for MAC,
although both drugs have activity against both
pathogens. MAC infections are most common
in patients with HIV, who are often taking
antiretroviral therapy that is metabolized by
CYP450. Because rifabutin has somewhat lesspotent
CYP450-inducing effects than rifampin,