Pirlimycin Hydrochloride

Lincosamide antibiotic Antibacterial

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Cattle (lactating dairy) Intramammary (IMM) One syringe (50 mg pirlimycin) per affected quarter Every 24 hours (q24h) Duration: 2 consecutive days (may be extended to 8 days for chronic cases)
Notes: Administer after milking. Clean and disinfect teat end before infusion. Massage quarter upward to distribute drug. For subclinical mastitis, treat all four quarters.

Clinical Indications & Species Uses

General Indications
  • Treatment of mastitis in lactating dairy cattle.
Cattle (Bovine)
  • Treatment of subclinical and clinical mastitis in lactating dairy cattle caused by Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, and other susceptible Gram-positive organisms.

Pharmacology & Mechanism of Action

Drug Class: Lincosamide antibiotic | Pharmacological Group: Antibacterial

Mechanism of Action: Pirlimycin is a lincosamide antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, specifically to the 23S rRNA of the 50S subunit, thereby blocking peptide bond formation and preventing chain elongation. This action is primarily bacteriostatic, but may be bactericidal at higher concentrations. It is active against Gram-positive bacteria and some anaerobes, but not against Gram-negative aerobes.

Pharmacodynamics: Pirlimycin exhibits time-dependent killing and has a post-antibiotic effect. Its activity is pH-dependent, with enhanced activity in acidic environments, which is relevant in the mammary gland. It is effective against Staphylococcus aureus (including penicillinase-producing strains), Streptococcus agalactiae, Streptococcus dysgalactiae, and other streptococci, as well as coagulase-negative staphylococci. It is not effective against Gram-negative bacteria or Mycoplasma.

⚡ Pharmacokinetics Summary

Absorption: After intramammary infusion, pirlimycin is absorbed systemically to a limited extent. The majority of the drug remains in the mammary gland, with peak milk concentrations occurring within 6-12 hours after administration. Systemic absorption is minimal, and the drug is primarily excreted in milk.
Distribution: Pirlimycin is distributed mainly into the mammary gland and milk. It binds to milk proteins to some extent. Systemic distribution is limited due to poor absorption from the mammary gland. It does not penetrate well into the central nervous system.
Metabolism: Pirlimycin is metabolized in the liver to a limited extent. The primary metabolite is N-demethylpirlimycin, which has reduced antibacterial activity. Metabolism is minimal compared to other lincosamides.
Excretion: The primary route of excretion is via milk, with a small amount excreted in urine and feces. In lactating cows, the majority of the administered dose is eliminated in milk over several days. In non-lactating animals, excretion is primarily via bile and feces.
Half-Life: In milk, the half-life is approximately 12-24 hours. Systemic half-life is not well characterized due to minimal absorption, but is estimated to be around 1-2 hours in plasma if absorbed.
Bioavailability: Oral bioavailability is poor and not used clinically. Intramammary administration results in high local concentrations in the udder, with minimal systemic bioavailability.
Protein Binding: Pirlimycin is approximately 50-60% bound to plasma proteins, but in milk, binding is higher due to milk protein content.

Available Formulations & Strengths

Intramammary infusion syringe 50 mg per syringe (10 mL) (Intramammary)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to pirlimycin or other lincosamides (e.g., lincomycin, clindamycin)
  • Do not use in animals with known sensitivity to lincosamides
  • Not for use in non-lactating dairy cattle (unless specifically indicated for dry cow therapy, but pirlimycin is not approved for dry cow use)
  • Not for use in calves or other non-lactating animals
Warnings & Clinical Precautions:
  • For intramammary use only in lactating dairy cattle
  • Do not administer intravenously or intramuscularly
  • Milk from treated cows must be discarded during treatment and for 36 hours after the last treatment
  • Treated animals must not be slaughtered for food until 9 days after the last treatment
  • Use with caution in animals with hepatic or renal impairment
  • Avoid contact with skin and eyes; wash hands after handling
  • Keep out of reach of children
  • Use aseptic technique during administration to prevent introduction of infection
  • Do not use in animals with a history of allergic reactions to lincosamides

Adverse Effects & Reactions

Common:

  • Local irritation at the infusion site
  • Swelling or inflammation of the udder
  • Discoloration of milk (usually transient)

Serious / Severe:

  • Allergic reactions (rare)
  • Anaphylaxis (rare)
  • Superinfection with resistant organisms (rare)

Rare:

  • Gastrointestinal disturbances if accidentally ingested
  • Systemic toxicity if accidentally injected

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Erythromycin and other macrolides May antagonize the antibacterial effect of pirlimycin due to competition for the same ribosomal binding site. Moderate
Chloramphenicol May antagonize the antibacterial effect of pirlimycin. Moderate
Neuromuscular blocking agents Lincosamides may enhance neuromuscular blockade, leading to respiratory depression. High

Overdose & Toxicity Management

Signs of Toxicity:

  • Local udder irritation
  • Swelling
  • Inflammation
  • Systemic signs if absorbed (e.g., gastrointestinal upset, ataxia, respiratory depression)

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. For local reactions, frequent milking and anti-inflammatory therapy may be helpful. If systemic signs occur, provide supportive care including respiratory support if needed.

Food Animal Withdrawal Times

🥩 Meat: 9 days🥛 Milk: 1.5 days

Milk discard period is 36 hours (1.5 days) after the last treatment. Slaughter withdrawal is 9 days after the last treatment. Not for use in animals producing milk for human consumption if the withdrawal period is not observed.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), with excursions permitted between 15-30°C (59-86°F).

Handling & Special Conditions: Protect from freezing. Store in original carton until ready to use.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved by FDA for intramammary use in lactating dairy cattle for the treatment of mastitis.

Extra-Label (Off-Label) Use: In the US, pirlimycin is approved for use in lactating dairy cattle only. Extra-label use in other species or for other indications requires a valid veterinary-client-patient relationship and must comply with AMDUCA regulations. Use in non-food animals is not common. For food animals, extra-label use may require extended withdrawal times.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Pirlimycin is a narrow-spectrum lincosamide antibiotic specifically formulated for intramammary administration in lactating dairy cattle. It is effective against Gram-positive mastitis pathogens, particularly staphylococci and streptococci. It is not effective against Gram-negative bacteria, so proper diagnosis of the causative agent is essential. Treatment should be initiated after milking, and the udder should be clean and dry. Complete the full course of therapy even if clinical signs improve. Monitor for local reactions. Adhere strictly to withdrawal times to ensure milk and meat safety. Pirlimycin is not used in other species due to lack of efficacy and safety data.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)