Tiamulin
**Tiamulin** is a semisynthetic diterpene pleuromutilin-class antibiotic primarily utilized in swine medicine. It is highly effective against *Mycoplasma* spp., spirochetes (such as *Treponema/Brachyspira hyodysenteriae*, the causative agent of swine dysentery), and various gram-positive cocci (including most *Staphylococcus* and *Streptococcus* species, excluding group D). While its activity against most gram-negative organisms is poor, it does maintain efficacy against *Haemophilus pleuropneumoniae* and select strains of *E. coli* and *Klebsiella*. > **Clinical Pearl:** Tiamulin's unique diterpene structure makes cross-resistance with other antibiotic classes less common. However, because it shares a ribosomal binding site with macrolides and lincosamides, concurrent use should be avoided to prevent competitive antagonism.
Mechanism: Tiamulin acts by binding to the **50S ribosomal subunit** at the peptidyl transferase center → blocks the correct positioning of tRNA → **inhibits bacterial protein synthesis**. It is generally **bacteriostatic**, but can become **bactericidal** at very high concentrations against highly susceptible organisms.
Dosing by species
- Swine dysentery · 7.7 mg/kg PO daily in drinking water · PO · q24h · 5 days · See package directions for dilution instructions.
- Swine pneumonia · 23.1 mg/kg PO daily in drinking water · PO · q24h · 5 days · See package directions for dilution instructions.
- Medicated premix · See the label for the product · PO · Continuous · Varies · Used for increased weight gain or disease control.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Concurrent access to feeds containing polyether ionophores (e.g., monensin, lasalocid, narasin, salinomycin)
- Swine weighing over 250 pounds
Adverse effects
- Skin redness/erythema (rare, primarily over the ham and underline)
Drug interactions
- Polyether ionophores (monensin, lasalocid, narasin, salinomycin) · Severe adverse reactions and potential toxicity can occur if administered to animals with access to these feed additives.
- Lincosamides and Macrolides (clindamycin, lincomycin, erythromycin, tylosin) · Concomitant use could lead to decreased efficacy secondary to competition at the 50S ribosomal binding site.
Monitoring
- Clinical efficacy (resolution of respiratory or enteric signs)
- Feed and water intake
Overdose
Oral overdoses in pigs may cause transient **salivation**, **vomiting**, and **CNS depression** (calming effect). **Management:** Discontinue the drug immediately and treat symptomatically and supportively if necessary. Provide clean, unmedicated drinking water.
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.