Lincomycin
**Lincomycin** is a narrow-to-medium spectrum **lincosamide antibiotic** closely related to clindamycin. It is primarily utilized in veterinary medicine to treat infections caused by susceptible gram-positive aerobic cocci (such as *Staphylococcus* and *Streptococcus* spp.), various anaerobic bacteria, and *Mycoplasma*. Key pharmacological characteristics include: - **Spectrum of Activity**: Effective against many anaerobes, gram-positive aerobes, and *Toxoplasma*. It is generally inactive against gram-negative aerobes and *Enterococcus faecalis*. - **Clinical Utility**: While FDA-approved for dogs, cats, and swine, its use in small animals has largely been supplanted by clindamycin, which boasts better oral bioavailability, higher intrinsic activity, and a lower toxicity profile. - **Toxicity Profile**: It is **strictly contraindicated** in hindgut fermenters and ruminants (e.g., horses, rabbits, rodents) due to the risk of severe, often fatal, clostridial enterocolitis. > **Clinical Pearl**: Lincomycin is a time-dependent antibiotic. Maintaining drug concentrations above the Minimum Inhibitory Concentration (MIC) for the duration of the dosing interval is critical for clinical success.
Mechanism: Lincomycin exerts its antibacterial effects by binding to the **50S ribosomal subunit** of susceptible bacteria. **Mechanism Pathway**: Drug enters bacterial cell โ Binds reversibly to the **50S ribosomal subunit** โ Blocks the transpeptidation and translocation steps โ **Inhibits bacterial protein synthesis**. Depending on the concentration of the drug at the infection site and the specific susceptibility of the targeted organism, lincomycin can be either **bacteriostatic** or **bactericidal**. > **Note**: Complete cross-resistance occurs between lincomycin and clindamycin, and partial cross-resistance occurs with macrolides like erythromycin due to overlapping ribosomal binding sites.
Dosing by species
- Skin and soft tissue infections ยท 11 mg/kg IM q12h or 22 mg/kg IM q24h ยท IM ยท q12h or q24h ยท 12 days or less
- Systemic infections ยท 15 mg/kg PO q8h or 22 mg/kg PO q12h ยท PO ยท q8h or q12h ยท 12 days or less
- Susceptible bacterial infections ยท 22 mg/kg ยท IM ยท q24h
- Susceptible bacterial infections ยท 11 mg/kg ยท IM ยท q12h
- Susceptible bacterial infections ยท 11-22 mg/kg ยท IV ยท q12-24h ยท Must be administered slowly
- Susceptible bacterial infections ยท 22 mg/kg ยท PO ยท q12h
- Susceptible bacterial infections ยท 15 mg/kg ยท PO ยท q8h
- Mycoplasmal (M. hyopneumoniae) pneumonia ยท Fed at 200 grams per ton of feed for 21 days or 11 mg/kg IM once daily ยท PO, IM ยท Continuous in feed or once daily IM ยท 21 days (feed)
- Susceptible infections ยท 11 mg/kg IM once daily for 3-7 days; or added to drinking water at a rate of 250 mg/gallon (average of 8.36 mg/kg/day) ยท IM, PO ยท Once daily (IM) or continuous in water ยท 3-7 days (IM)
- Susceptible infections ยท 10-15 mg/kg PO three times daily; 10 mg/kg IM twice daily ยท PO, IM ยท Three times daily (PO) or twice daily (IM)
Routes of administration
Contraindications
- Rabbits
- Hamsters
- Guinea pigs
- Horses
- Ruminants (cattle, sheep, goats)
- Patients with known hypersensitivity to lincosamides
- Patients with preexisting monilial (yeast) infections
- Neonatal animals (relative contraindication due to gut flora effects)
- Rapid intravenous administration
- Known hypersensitivity to lincosamides
- Use with caution in patients with severe liver disease
Adverse effects
- Gastroenteritis (emesis, loose stools, bloody diarrhea in dogs)
- Pain and inflammation at IM injection sites
- Hypotension and cardiopulmonary arrest (if administered rapidly IV)
- Gastrointestinal disturbances in swine
- Diarrhea in nursing neonates (drug distributes into milk)
- Diarrhoea (potentially haemorrhagic)
- Colitis
- Hepatotoxicity (in patients with pre-existing liver disease)
- Cardiac depression (if given rapidly IV)
- Peripheral neuromuscular blockade (if given rapidly IV)
Drug interactions
- Cyclosporine ยท Lincomycin may reduce systemic levels of cyclosporine.
- Erythromycin ยท In vitro antagonism occurs due to competing ribosomal binding sites; concomitant use should be avoided.
- Kaolin ยท Reduces the absorption of oral lincomycin by up to 90%. If both are necessary, separate doses by at least 2 hours. ยท moderate
- Neuromuscular blocking agents (e.g., pancuronium) ยท Lincomycin possesses intrinsic neuromuscular blocking activity and may enhance the effects of these agents; use cautiously.
- Neuromuscular blocking agents ยท Enhanced neuromuscular blockade action ยท major
- Chloramphenicol ยท Antagonistic antimicrobial action (competes for 50S ribosomal binding site) ยท major
- Macrolides ยท Antagonistic antimicrobial action (competes for 50S ribosomal binding site) ยท major
Monitoring
- Clinical efficacy (resolution of infection)
- Adverse effects, particularly severe or bloody diarrhea
- Liver function tests (AST, ALT, Alk. Phosph.) may show slight, usually clinically insignificant, increases
- Fecal consistency (monitor for diarrhoea or haemorrhagic stool)
- Liver enzymes (in patients with pre-existing hepatic impairment)
Overdose
There is limited information regarding acute overdoses. Lincomycin appears to have a wide margin of safety in dogs. Oral doses up to 300 mg/kg/day for up to one year, or parenteral doses of 60 mg/kg/day, did not result in apparent toxicity. If a massive overdose occurs, standard supportive care and gastrointestinal decontamination (if oral and recent) should be considered.
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.