Rifamycins

Question 1

Rifamycins

Answer 1

Rifampin (Rifampicin)
Rifabutin
Rifapentine
Rifaximin (not used for mycobacterial disease)

Cornerstones of therapy for TB and MAC
Protein synthesis inhibitors- inhibit transcription of DNA to bacterial mRNA

Rifampin is one of the two most important drugs in TB

Potent inducers of cytochrome P450 system
Always screen for drug interactions

Also active against many typical bacteria (sometimes added on to other therapies like difficult to treat MRSA)

Question 2

Rifamycins MOA

Answer 2

Protein synthesis inhibitors that work by inhibiting RNA polymerase- preventing transcription by blocking production of mRNA

Other protein synthesis inhibitors inhibit translation

Question 3

Rifamycins Spectrum

Answer 3

Good
Most mycobacteria

Moderate
Staph
Acinetobacter
Enterobacteriaceae

Poor
Typical bacteria as monotherapy
Some very rare mycobacteria

Question 4

Rifamycins Adverse Effects

Answer 4

Generally well tolerated
Most notorious for potent CYP450 inducing effects
Can manifest as sub therapeutic concentrations; loss of seizure control (anticonvulsants); organ rejection (antirejection agents)

Colors secretions (urine, tears) orange-red
Can stain contact lenses (do not wear during therapy)
Is non permanent and not harmful 

Can cause hepatotoxicity

Rash
N/V
Hypersensitivity (often fever)

Question 5

Rifamycins Important Facts

Answer 5

Rifampin is drug of choice for TB
Rifabutin drug of choice for MAC
Both drugs have activity against both pathogens

MAC most common in patients with HIV (often take antiretroviral drugs metabolized by CYP450)
Rifabutin has somewhat less potent inducing effects than Rifampin so it’s more commonly used for MAC

Rifampin/Rifabutin one of two most important drugs for TB (isoniazid is the other)
If isolate is resistant, will require more complicated regimens for longer and likely less successful

Rifapentine is a second line drug given once weekly
If isolate is resistant to one rifamycin, it’s resistant to all
Given with isoniazid as once weekly therapy for latent TB

Rifaximin is non-absorbed rifamycin used only in treatment and prevention of GI conditions
Not used for mycobacterial diseases

Rifamycins should not be used alone for active TB
Rifampin can be used alone for latent TB

Question 6

Rifamycins Good For

Answer 6

Treatment of active TB and MAC in combo with other drugs

Latent TB

Select bacterial infections in combo with standard antibacterials (most notably bacterial infections involving prosthetic material- like artificial hip or heart valve)