Tylosin
Tylosin is a macrolide antibiotic naturally produced by *Streptomyces fradiae*. While primarily FDA-approved for use in livestock (cattle and swine) to treat respiratory and enteric infections, it is a staple in small animal medicine for managing **Tylosin-Responsive Diarrhea (TRD)**, chronic colitis, and inflammatory bowel disease (IBD). **Key Clinical Pearls:** * **Microbiome Modulation:** In dogs, tylosin is uniquely effective for TRD. This is likely due to its ability to modulate the intestinal microbiome (specifically promoting beneficial *Enterococcus* spp.) and its immunomodulatory effects, rather than purely through its direct antimicrobial properties. * **Epiphora Management:** It has been used anecdotally to reduce tear staining (epiphora) in dogs (e.g., Maltese, Poodles) by binding porphyrins or altering normal flora, though this use is controversial due to antimicrobial stewardship concerns. * **FIP:** Anecdotally used in cats as an immunomodulating agent for Feline Infectious Peritonitis (FIP), though evidence is limited.
Mechanism: Tylosin shares a mechanism of action with erythromycin: * **Antimicrobial Action:** Binds reversibly to the **50S ribosomal subunit** of susceptible bacteria โ inhibits translocation of peptides โ prevents protein synthesis. It is primarily **bacteriostatic**, but can be bactericidal at high concentrations. * **Spectrum of Activity:** Effective against Gram-positive bacteria, *Mycoplasma*, *Chlamydia*, and some Gram-negative anaerobes (e.g., *Clostridium perfringens*). * **Immunomodulation & Probiotic Effect:** Alters cell-mediated immunity. In dogs, it specifically increases jejunal concentrations of *Enterococcus faecalis*, which acts as a probiotic to stabilize the gut barrier and resolve chronic diarrhea.
Dosing by species
- Adjunctive treatment of IBD ยท 10 mg/kg ยท PO ยท TID ยท 21 days ยท Therapeutic trial to evaluate efficacy
- IBD or diarrheas caused by C. perfringens ยท 20-40 mg/kg ยท PO ยท BID
- IBD ยท 40 mg/kg ยท PO ยท q12h
- Clostridial colitis ยท 10-40 mg/kg ยท PO ยท BID ยท Practically: 1/16 tsp 2-3x/day. Chronic cases often controlled with 1 treatment every 2-3 days.
- Susceptible infections ยท 7-15 mg/kg ยท PO ยท q12-24h
- Susceptible infections ยท 8.8 mg/kg ยท IM ยท BID ยท up to 3 days ยท Continue 24h after symptoms stop. Max 5 mL/site.
- Susceptible infections ยท 5-10 mg/kg ยท IM ยท up to 3 days ยท Until 24h after remission
- Susceptible infections ยท 12.5 mg/kg ยท IM ยท q12h ยท Tylosin base injectable
- Susceptible infections ยท 10 mg/kg ยท PO ยท SID to BID
- Susceptible infections ยท 10 mg/kg ยท up to 5 days
Routes of administration
Contraindications
- Hypersensitivity to tylosin or other macrolide antibiotics
- Horses (causes severe and potentially fatal dysbiosis/diarrhea)
- No specific contraindications available in the monograph
Adverse effects
- Pain and local reactions at IM injection sites
- Mild GI upset (anorexia, diarrhea) in small animals
- Severe/fatal diarrhea in horses (any route)
- Severe diarrhea in ruminants (PO)
- Swine: edema of rectal mucosa, mild anal protrusion with pruritus, erythema, and diarrhea
- Gastrointestinal disturbances
- Pain at the site of injection
Drug interactions
- Digoxin ยท May increase digoxin blood levels, potentially resulting in toxicity
Monitoring
- Clinical efficacy (resolution of diarrhea or infection)
- Adverse effects (GI upset, injection site reactions)
- Clinical response (resolution of diarrhea or infection)
- Injection site for pain or inflammation
Overdose
Tylosin is relatively safe in most overdose situations. * **Dogs:** Tolerate oral doses up to 800 mg/kg. Long-term (2-year) oral administration of up to 400 mg/kg produced no organ toxicity. * **Pigs:** LD50 is >5 g/kg PO, and ~1 g/kg IM. However, shock and death have been reported in baby pigs overdosed with tylosin.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.