Rifampin
Rifampicin (semi-synthetic zwitterion derivative of rifamycin B)
Also known as: Rifadin · Rimactane · Ba-41166/E · L-5103 · NSC-113926 · rifaldazine · rifampicinum · rifamycin AMP · Rifampin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Combination therapy of atypical Mycobacteria infections; treatment of resistant Staph endocarditis | 10-20 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
| Alternate treatment for scarred pyogranulomatous pyoderma | 5-10 mg/kg PO q24h | PO | q24h | 4-8 weeks | 🌎 NA |
| Actinomycosis | 10-20 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Susceptible infections (e.g., mycobacteriosis, resistant staphylococcal pyoderma, ehrlichiosis) | 10-15 mg/kg | PO | q24h | Duration depends on the specific infection being treated | 🌍 EU |
- Combination therapy of atypical Mycobacteria infections; treatment of resistant Staph endocarditis: In combination with amoxicillin/clavulanate or trimethoprim/sulfa
- Alternate treatment for scarred pyogranulomatous pyoderma: Must be used with another antibiotic to reduce risk for resistance development (e.g., cephalexin or a potentiated sulfonamide). Monitor CBC, liver screens, and UA every 2 to 3 weeks.
- Susceptible infections (e.g., mycobacteriosis, resistant staphylococcal pyoderma, ehrlichiosis): Must be used in combination with other antimicrobial drugs to prevent the emergence of resistant organisms.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (e.g., mycobacteriosis, Rhodococcus equi, chlamydiosis, bartonellosis) | 10-15 mg/kg | PO | q24h | Duration depends on the specific infection being treated | 🌍 EU |
- Susceptible infections (e.g., mycobacteriosis, Rhodococcus equi, chlamydiosis, bartonellosis): Must be used in combination with other antimicrobial drugs to prevent the emergence of resistant organisms.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of mycobacteriosis | 45 mg/kg PO once daily | PO | q24h | — | 🌎 NA |
- Treatment of mycobacteriosis: In combination with ethambutol (30 mg/kg PO once daily) and one of the following: clofazimine (6 mg/kg PO once daily) or isoniazid (30 mg/kg PO once daily).
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of Rhodococcus equi (C. equi) infections in foals | 5 mg/kg PO two times daily | PO | q12h | — | 🌎 NA |
| Treatment of Rhodococcus equi (C. equi) infections in foals | 5 mg/kg PO two times daily or 10 mg/kg PO once daily | PO | q12h or q24h | 4-9 weeks | 🌎 NA |
| Treatment of proliferative enteropathy caused by Lawsonia intracellularis in foals | 10 mg/kg PO once daily | PO | q24h | minimum of 21 days | 🌎 NA |
- Treatment of Rhodococcus equi (C. equi) infections in foals: With erythromycin 15-25 mg/kg, PO q12-24h. Clarithromycin may be superior due to erythromycin side effects.
- Treatment of Rhodococcus equi (C. equi) infections in foals: With erythromycin 25 mg/kg, PO q6-8h.
- Treatment of proliferative enteropathy caused by Lawsonia intracellularis in foals: In combination with erythromycin estolate (25 mg/kg PO q6-8h)
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Rifampin is a highly lipophilic, semi-synthetic antimicrobial agent belonging to the rifamycin class. It is a cornerstone therapy in veterinary medicine for treating deep-seated, intracellular infections, most notably Rhodococcus equi in foals.
Because of its exceptional ability to penetrate caseous material, bone, abscesses, and macrophages, it is highly effective against intracellular pathogens like Mycobacterium spp., Staphylococcus aureus, and Lawsonia intracellularis. It also possesses some antifungal and antiviral activity at high concentrations.
Clinical Pearl: Rifampin must never be used as a monotherapy. Bacteria can develop resistance rapidly via a single-step mutation. It is always prescribed in combination with other antimicrobials (e.g., macrolides like erythromycin or clarithromycin in horses, or cephalosporins/sulfonamides in dogs).
Mechanism of action
Rifampin can be bactericidal or bacteriostatic depending on the concentration and the susceptibility of the target organism.
- Target: It binds strongly to the beta subunit of bacterial DNA-dependent RNA polymerase.
- Pathway: Binding inhibits the enzyme → suppresses the initiation of chain formation for RNA synthesis → halts bacterial protein production → cell death.
- Selectivity: Rifampin is highly selective for bacterial enzymes and does not inhibit mammalian RNA polymerase, providing a wide margin of safety for the host.
Safety & warnings
Contraindications
- Hypersensitivity to rifampin or other rifamycins
- Use with extreme caution in patients with preexisting hepatic dysfunction
- Pregnancy (teratogenic at high doses)
- Pre-existing liver disease or hepatic dysfunction
Adverse effects
- Red-orange discoloration of bodily fluids (urine, tears, sweat, saliva)
- Gastrointestinal distress (anorexia, vomiting, diarrhea)
- Elevated liver enzymes and potential hepatotoxicity
- Rashes and erythema (noted in cats and humans)
- In horses (especially with macrolides): mild diarrhea to severe enterocolitis, hyperthermia, and acute respiratory distress
- Intravenous use in horses (rare): CNS depression, sweating, hemolysis, anorexia
- Elevated serum hepatic enzymes
- Clinical hepatitis
- Orange-red discoloration of urine, saliva, tears, and feces
- Gastrointestinal upset (anorexia, vomiting, diarrhea)
Precautions
Use with caution in patients with preexisting hepatic dysfunction; dosage reduction may be necessary. Never use as a monotherapy due to the rapid development of bacterial resistance. Rifampin is a potent inducer of hepatic microsomal enzymes, which can significantly alter the metabolism of concurrently administered drugs. It is excreted in maternal milk; use with caution in nursing veterinary patients. May cause false-positive BSP (bromosulfophthalein) test results and interfere with microbiologic assays of serum folate and vitamin B12.
Drug interactions
In vitro antagonism has been reported; concurrent use should be avoided.
Decreased serum levels and shortened half-life due to hepatic microsomal enzyme induction by rifampin.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Decreased serum levels and shortened half-life due to hepatic enzyme induction.
Increased rate of metabolism of theophylline due to hepatic enzyme induction.
Increased rate of metabolism of itraconazole due to hepatic enzyme induction, leading to subtherapeutic antifungal levels.
Monitoring
- Clinical efficacy and resolution of infection
- Liver function tests (especially with long-term therapy)
- Chest radiographs and plasma fibrinogen levels (prognostic indicators for C. equi infections in foals after 1 week of therapy)
- Baseline and periodic serum hepatic enzyme levels (ALT, AST, ALP, Bilirubin)
- Clinical signs of hepatitis (icterus, anorexia, vomiting, lethargy)
Pharmacokinetics
Half-life
Absorption
Relatively well absorbed from the GI tract. Oral bioavailability is about 40-70% in horses and 37% in adult sheep. Concurrent food administration may delay and slightly reduce peak plasma levels.
Distribution
Very lipophilic. Readily penetrates most body tissues (including bone and prostate), cells, and fluids (including CSF). Uniquely penetrates abscesses and caseous material. 70-90% bound to serum proteins. Distributes into milk and crosses the placenta. Volume of distribution is ~0.9 L/kg in horses and 1.3 L/kg in sheep.
Metabolism
Metabolized in the liver to a deacetylated form that retains antibacterial activity. Rifampin induces hepatic microsomal enzymes, meaning elimination rates may increase over time with repeated dosing (auto-induction).
Elimination
Both the active metabolite and unchanged drug are excreted primarily in the bile, but up to 30% may be excreted in the urine. The parent drug undergoes substantial enterohepatic recirculation, but the metabolite does not.
Overdose
Clinical signs of oral rifampin overdose are generally extensions of its adverse effects, including gastrointestinal distress, orange-red coloring of fluids, and skin erythema (noted particularly in cats).
Massive overdoses carry a significant risk of hepatotoxicity. Dogs may exhibit central nervous system depression.
Treatment:
- Empty the gut following standard decontamination protocols for massive oral overdosage.
- Monitor liver enzymes closely.
- Initiate supportive treatment as necessary.
Available products
Formulations
- Oral capsules
- Lyophilized powder for injection
- 150 mg capsule
- 300 mg capsule
- 20 mg/ml syrup
Human-labeled
- Rifampin Oral Capsules: 150 mg & 300 mg (Rifadin®, Rimactane®, generic)
- Rifampin Lyophilized Powder for Injection Solution: 600 mg (Rifadin®, generic)
- Rifadin 150 mg capsules
- Rifadin 300 mg capsules
- Rifadin 20 mg/ml syrup
- Rimactane capsules
Regulatory status
Human authorized products used under the prescribing cascade. Rifamycins are critically important antimicrobials.
POM (Prescription Only Medicine). Used under the cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Rifampin capsules should be stored in tight, light-resistant containers, preferably at room temperature (15-30°C).
Client information
- Harmless Discoloration: This medication will likely cause your pet's urine, tears, sweat, and saliva to turn a red-orange color. This is completely normal and harmless, but be aware that it can permanently stain fabrics, carpets, or light-colored fur.
- Administration: For the best absorption, give this medication on an empty stomach. If it causes stomach upset, you may give it with a small treat.
- Combination Therapy: Rifampin is almost always prescribed alongside another antibiotic. It is critical to give both medications exactly as directed and finish the entire course. Never stop early, as bacteria can quickly become resistant to rifampin.
- What to Watch For: Contact your veterinarian if you notice severe diarrhea, loss of appetite, extreme lethargy, or yellowing of the eyes/gums (jaundice), as these could be signs of liver stress.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.