An antibiotic is a substance that kills bacteria or inhibits their growth. The term originally referred to compounds derived from other microorganisms — penicillin from mold, streptomycin from soil bacteria — but is now applied broadly to any drug targeting bacterial cell walls, protein synthesis, DNA replication, or membrane function, whether natural or synthetic in origin.
Antibiotics used in horses include penicillin (gram-positive organisms, common in wounds and respiratory infections), trimethoprim-sulfamethoxazole (broad-spectrum oral, commonly used for wounds and respiratory disease), enrofloxacin (fluoroquinolone, gram-negative coverage), gentamicin (aminoglycoside, joint infections via regional perfusion), and metronidazole (anaerobic infections, colitis). Tetracyclines such as doxycycline are used for rickettsial diseases including Potomac Horse Fever and Lyme disease. No antibiotic should be administered to a horse without veterinary oversight: inappropriate antibiotic use can disrupt the hindgut microbiome and trigger colitis, sometimes fatally.
Antibiotic resistance is an active concern in equine medicine. Extended treatment courses, failure to complete prescribed courses, and use of broad-spectrum drugs for infections that culture to sensitive organisms are the primary drivers. The relationship between antibiotic stewardship and long-term herd health is addressed in the vaccination and preventive care framework. Antibiotic use is distinct from parasite control with anthelmintics, which targets worms rather than bacteria; both are tools in equine medicine with their own resistance concerns. First-time owners should understand that obtaining an antibiotic without a valid veterinarian-client-patient relationship is both legally restricted and medically risky.
Further Reading
- Antibiotics — Wikipedia entry on the discovery, classes, and mechanisms of antibacterial drugs.
- Penicillins in equine practice — Merck Veterinary Manual on penicillin pharmacokinetics, spectrum, and dosing in horses.