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.