In-depth Notes on Antimicrobial Drugs 2

Antibiotics Affecting Protein Synthesis

Aminoglycosides

  • Common Drugs: Gentamicin, Amikacin, Kanamycin, Tobramycin, Neomycin, Streptomycin, Dihydrostreptomycin
  • Note: Not all drugs ending with -micin or -mycin are aminoglycosides.

Tetracyclines

  • Characteristics:
    • Bacteriostatic (inhibits bacterial growth)
    • Broad spectrum antibacterial.
  • Uses:
    • Lyme disease (Borreliosis)
    • Leptospirosis
    • Chlamydial infections (cats, birds)
    • Mycoplasma pneumonia
    • Rickettsial infections (e.g., Ehrlichia)
  • Resistance: Common occurrence.
  • Precautions:
    • Binds with minerals (calcium, magnesium, iron); renders ineffective if given orally.
    • Avoid giving with dairy, mineral supplements, or antacids.
    • Contraindicated for use in pregnant or juvenile animals due to potential for staining teeth and bones.
  • Types: Tetracycline, Oxytetracycline, Chlortetracycline, Doxycycline, Minocycline.

Phenicols

  • Characteristics:
    • Broad-spectrum
    • Bacteriostatic
    • Penetrate tissues including CNS and eyes well.
  • Examples: Chloramphenicol, Florfenicol.

Macrolides

  • Characteristics:
    • Primarily effective against gram-positive bacteria.
    • Can be bactericidal or bacteriostatic.
  • Examples: Erythromycin, Tylosin (Tylan®), Tulathromycin (Draxxin®), Tilmicosin (Micotil®), Azithromycin.
  • Usage Notes:
    • Erythromycin is useful in penicillin-resistant cases.
    • Tylosin is used in livestock but is fatal in horses.
    • Tilmicosin has a risk of fatal cardiotoxicity in certain species.

Lincosamides

  • Characteristics:
    • Effective against anaerobes and aerobes.
    • Good for deep infections and abscesses.
  • Adverse Effects: Can cause serious GI problems.
  • Contraindications: Not to be used in horses, guinea pigs, hamsters, rabbits, chinchillas, or ruminants.
  • Examples: Lincomycin, Clindamycin (e.g., Antirobe®).

Antibiotics Affecting Metabolism: Sulfonamides

  • Mechanism: Inhibit synthesis of folic acid, needed by many bacteria.
  • Action: Bacteriostatic unless potentiated, effective against Gram (+) bacteria.
  • Ineffective in: Pus/necrotic tissue.
  • Legal Note: Extra-label drug use prohibited in food animals.
  • Types:
    • Not potentiated: Sulfasalazine, Sulfadimethoxine (Albon®)
    • Potentiated: Sulfadimethoxine (+ ormetoprim) (Primor®), Sulfadiazine (+ trimethoprim) (Tribrissen®), Sulfamethoxazole (+ trimethoprim) (Septra®).
  • Precautions:
    • Hypersensitivity reactions common.
    • Can cause photosensitivity, keratoconjunctivitis sicca (KCS), kidney damage, and thrombocytopenia.

Antibiotics Affecting DNA Replication: Fluoroquinolones

  • Characteristics: Concentration dependent, bactericidal, broad spectrum.
  • Examples: Enrofloxacin (Baytril®, Baytril Otic®), Ciprofloxacin, Marbofloxacin (Zeniquin®), Orbifloxacin (Orbax®, Posatex®).
  • Precautions:
    • Absorption decreased by food, mineral supplements, and antacids.
    • Teratogenic effects; contraindicated in pregnant/nursing or juvenile animals.
    • Possible irreversible retinal damage in cats at high dosages.
  • Legal Note: Prohibited in food animals.

Miscellaneous Antibiotics

  • Nitrofurans:
    • Broad-spectrum
    • Carcinogenic in humans; prohibited in food-producing animals.
    • Examples include nitrofurantoin, nitrofurazone.
  • Metronidazole:
    • Bactericidal against anaerobes and an antiprotozoal.
    • Prohibited in food animals; can cause neurotoxicity at high dosages/long treatment durations.
  • Rifampin:
    • Broad spectrum, primarily used with erythromycin for treating Rhodococcus equi pneumonia in young foals.
    • Can color urine, tears, sweat, and saliva reddish-orange.