Rifampin

Rifampin, also called rifampicin, is a rifamycin antibacterial with useful intracellular and tissue distribution. A major veterinary application is combination treatment of Rhodococcus equi infection in foals. It is also used for selected susceptible staphylococcal, mycobacterial and other intracellular infections, usually within an organism-directed combination plan.

Group

Rifamycin antibacterial

Mechanism of Action

Rifampin binds the beta subunit of bacterial DNA-dependent RNA polymerase and inhibits initiation of RNA synthesis. Interruption of transcription prevents production of essential proteins and can produce bactericidal activity in susceptible organisms. Lipid solubility supports intracellular penetration and activity against some intracellular pathogens. Target mutations and other resistance mechanisms determine whether the organism remains susceptible.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	5 mg/kg	PO	Every 12 h	Lower divided regimen preferred.
Susceptible bacterial infection	10 mg/kg	PO	Every 24 h
Mycobacterial or resistant staphylococcal combination treatment	10–20 mg/kg	PO	Every 8–12 h	Use with another effective antimicrobial to reduce resistance; monitor hepatic toxicity.
Pyogranulomatous pyoderma combination treatment	5–10 mg/kg	PO	Every 24 h	Up to 56 days; Reported 4-8 weeks with another effective antibiotic.
Actinomycosis	10–20 mg/kg	PO	Every 12 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	5 mg/kg	PO	Every 12 h	Lower divided regimen preferred.
Susceptible bacterial infection	10 mg/kg	PO	Every 24 h

Horses

Use / stage	Dose	Route	Schedule	Instructions
Susceptible bacterial infection	10 mg/kg	PO	Every 24 h
Rhodococcus equi infection	5 mg/kg	PO	Every 12 h	Foals; reported regimen describes possible erythromycin 25 mg/kg PO every 8 hours or another macrolide; combination benefit is not established by this monograph.
Foal proliferative enteropathy adjunct	10 mg/kg	PO	Every 24 h	With erythromycin estolate 25 mg/kg PO every 6-8 hours; at least 21 days.

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Reported susceptible infection treatment	20 mg/kg	PO	Every 24 h	Johne disease discussion includes combination with isoniazid without a complete companion protocol.

Sheep

Use / stage	Dose	Route	Schedule	Instructions
Reported susceptible infection treatment	20 mg/kg	PO	Every 24 h	Johne disease discussion includes combination with isoniazid without a complete companion protocol.

Goat

Use / stage	Dose	Route	Schedule	Instructions
Reported susceptible infection treatment	20 mg/kg	PO	Every 24 h	Johne disease discussion includes combination with isoniazid without a complete companion protocol.

Birds

Use / stage	Dose	Route	Schedule	Instructions
Mycobacteriosis combination treatment	45 mg/kg	PO	Every 24 h	With ethambutol 30 mg/kg PO daily plus clofazimine 6 mg/kg daily or isoniazid 30 mg/kg daily; individualize avian monitoring.

Indications

Combination treatment of Rhodococcus equi pneumonia or associated infections in foals, commonly with a macrolide.
Combination treatment of selected susceptible mycobacterial infections in veterinary patients.
Treatment of selected susceptible resistant staphylococcal infections, including some deep pyoderma or implant-associated infections.
Treatment of selected susceptible granulomatous or intracellular bacterial infections within a specialist antimicrobial plan.
Selected combination treatment of Lawsonia intracellularis-associated proliferative enteropathy in foals, with a smaller evidence base.

Contraindications

Pregnancy
Hepatotoxicity or pancreatitis risk requires caution.

Interactions

Potently induces hepatic enzymes and P-glycoprotein, lowering exposure to many drugs including macrolides, anticonvulsants, corticosteroids, digoxin and warfarin.

Adverse effects

Vomiting, anorexia, diarrhea, hepatotoxicity and harmless orange-red body-fluid discoloration.

Toxicity

Severe exposure can cause hepatic injury in addition to GI and CNS effects. Monitor liver enzymes and bilirubin and provide supportive care.

Preparations

Preparation	Form	Strength	Route
Rifampin capsule 150 mg	Capsule	150 mg / capsule	PO
Rifampin capsule 300 mg	Capsule	300 mg / capsule	PO
Rifampin IV vial 600 mg	Injection	600 mg / vial	IV

Monitoring and Administration

Assess liver enzymes and bilirubin after about 7 days and every 10-14 days thereafter; discontinue if hepatic injury develops. Antibacterial resistance and combination plans require microbiologic assessment.

Light-protected oral syrup preparations have reported stability of 4-6 weeks. Reported reconstituted IV solution 60 mg/mL is stable for 24 hours.

Resistance can emerge rapidly with monotherapy; use another effective antimicrobial when indicated. The comparative benefit of combination treatment for foal R. equi disease remains uncertain. Macrolide-containing foal courses often last 4-9 weeks and can cause hyperthermia and severe enterocolitis in foals or mares.