Tilmicosin
**Tilmicosin** is a semi-synthetic **macrolide antibiotic** synthesized from tylosin, primarily used in veterinary medicine for the treatment of bovine and ovine respiratory disease (BRD) associated with *Mannheimia haemolytica*, *Pasteurella multocida*, and *Histophilus somni*. * **Key Features**: * Highly lipophilic, allowing for extensive tissue penetration. It actively concentrates in **lung tissue** and alveolar macrophages, providing targeted therapy for respiratory infections. * Administered primarily via **subcutaneous (SC)** injection in ruminants or as a medicated feed additive in swine. > **CRITICAL WARNING**: Tilmicosin has a narrow margin of safety in many species. Accidental injection in humans, swine, horses, camelids, and non-human primates can be **rapidly fatal** due to severe cardiovascular toxicity.
Mechanism: Tilmicosin exerts its bacteriostatic effect by penetrating the bacterial cell membrane and reversibly binding to the **50S ribosomal subunit**. * **Mechanism**: Binds to the **50S subunit** → blocks the exit tunnel for newly synthesized peptides → inhibits translocation of peptidyl-tRNA → **premature termination of bacterial protein synthesis**. * It exhibits time-dependent antibacterial activity and has a prolonged post-antibiotic effect (PAE), especially against respiratory pathogens. Its accumulation in macrophages allows it to be delivered directly to the site of infection via chemotaxis.
Dosing by species
- Susceptible infections · 10 mg/kg SC (not more than 15 mL per injection site). · SC · Single dose · Subcutaneous injection under the skin in the neck, or if not accessible, behind the shoulders and over the ribs is suggested. Do not use in lambs less than 15 kg of body weight.
- Treatment of pneumonic pasteurellosis · 10 mg/kg SC every 72 hours · SC · q72h · Subcutaneous injection under the skin in the neck, or if not accessible, behind the shoulders and over the ribs is suggested.
- Susceptible infections · 10 mg/kg SC (not more than 15 mL per injection site) · SC · Single dose
- Susceptible infections (Rabbits) - Regimen 1 · 25 mg/kg SC once; repeat in 3 days if necessary. · SC · Once, repeat in 3 days PRN · Can cause weakness, pallor, tachypnea and sudden death. May cause acute death if given IV. SC injections can cause local swelling and necrosis.
- Susceptible infections (Rabbits) - Regimen 2 · 5 mg/kg SC on day 0, if no reaction, give 10 mg/kg SC on days 7 and 14. · SC · Days 0, 7, 14 · 14 days · Can cause weakness, pallor, tachypnea and sudden death. May cause acute death if given IV. SC injections can cause local swelling and necrosis.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Intravenous (IV) administration (can be fatal)
- Use in automatically powered syringes
- Injection in swine, non-human primates, horses, and camelids
- Use in lactating ewes if milk is intended for human consumption
- Use in veal calves
- Use in female dairy cattle 20 months or older
Adverse effects
- Local tissue reaction and trim loss (if given IM)
- Edema at the site of subcutaneous injection
- Severe cardiovascular toxicity (fatalities) if given IV
- Fatalities in swine, non-human primates, and potentially horses if injected
- Severe reactions in camelids
Drug interactions
- Epinephrine · Increased mortality associated with tilmicosin in swine.
- Other Macrolides / Lincosamides · Potential cross-resistance and competitive binding at the 50S ribosomal subunit (extrapolated from erythromycin).
Monitoring
- Clinical efficacy (resolution of respiratory signs)
- Injection site reactions
- Slaughter withdrawal times (28 days for cattle/sheep injection; 7 days for swine feed)
Overdose
The **cardiovascular system** is the primary target of acute toxicity, likely due to calcium channel blockade leading to negative inotropic effects, tachycardia, and fatal arrhythmias. * **Cattle**: Doses up to 50 mg/kg IM did not cause death, but SC doses of 150 mg/kg caused fatalities, as did IV doses of 5 mg/kg. * **Swine**: Doses as low as 10 mg/kg caused increased respiration, emesis, and seizures; 20 mg/kg IM caused death in most animals tested. * **Monkeys**: 10 mg/kg caused no signs of toxicity; 20 mg/kg caused vomiting; 30 mg/kg caused death. > **HUMAN EXPOSURE**: In cases of human injection, **contact a physician immediately**. Apply ice to the injection site. Emergency medical telephone numbers: 1-800-722-0987 or 1-317-276-2000.
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.