Antibiotics Overview Quiz

Antibiotics

• Chloramphenicol
  • Interferes with microbial protein synthesis, attaching to ribosomes, preventing vital protein production.
  • Bacteriostatic at low doses, inhibiting the action of penicillins and cephalosporins.
  • Bactericidal at high doses (high concentrations).
  • Major concern: affects mitochondrial function in bone marrow cells, causing serious and fatal aplastic anemia in humans.
  • Not used in food animals.
  • Poor liver metabolism in cats, excreted via kidneys/bile.
• Tetracyclines
  • Bacteriostatic, inhibits bacterial protein synthesis.
  • Resistance is common.
  • Synergistic with other antibiotics, like tetracycline.
  • Variable absorption among different types.
  • Older tetracyclines are hydrophilic.
  • Newer tetracyclines are lipophilic.
  • Tetracycline & oxytetracycline can be chelated (bound to minerals).
• Aminoglycosides
  • Inhibit protein synthesis, causing bacterial cell division inhibition.
  • Mostly bactericidal (dose-related).
  • All administered parenterally (except neomycin).
  • Major concerns include nephrotoxicity (100% excreted via kidney), and ototoxicity (rare, increased risk with diuretics).
  • Mostly remain in extracellular fluid.
• Rifamycins
  • Not an aminoglycoside, but used mostly in horses.
  • Combined with b-lactams and doxycycline.
  • Resistance to rifampin is common.
  • Red-orange coloration of urine, tears, and saliva in horses.
  • Wear gloves when handling.
• Aminocyclitols: Lincosamides and Macrolides
  • Inhibit bacterial protein synthesis (bacteriostatic or bactericidal, depending on the drug).

Chloramphenicol (CAP) Considerations

• Resistance can be a problem, potentially involving cross-resistance with other antibiotics.
• Synergistic with tetracycline.
• Rapid absorption in all tissues.
• Intravenous (IV), intramuscular (IM), or oral (PO) administration.
• IV dosing is 4-5 times per day due to absorption.
• Some CAP is excreted unchanged by the kidneys, useful for urinary tract infections.
  • T1/2:
    • Horses: 1 hour or less.
    • Foals: 6+ hours.
    • Cats: 5-6 hours (much lower doses).
    • Dogs: 3-4 hours.
• Common forms include: Azramycine®, Centracol®, Chlor Palm®, Chlor Tablets®, Karomycin Palmitate®, Rogar Mycine®, Zoommycetine® Palmitate.
• Available as tablets, oral suspension, and injections.
• Well-absorbed, especially orally, and widely distributed.

Florfenicol (Nuflor®)

• Related to chloramphenicols, but modified.
• Safely used in cattle for respiratory disease, pneumonia, and foot rot.
• Dosage: 2 x IM injections (20mg/kg, 48 hours apart) or 1 x SQ high dose injection (40mg/kg).
• Withdrawal time: 38 days.
• IM injection may cause tissue reactions, potentially leading to trim loss.
• Tissue reaction is more severe outside the neck region.

Zeleris®

• Approved in 2020.
• Medicinal ingredients: florfenicol, meloxicam.
• Used for bovine respiratory disease with accompanying fever.
• Associated pathogens: Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni.
• Approved for beef and non-lactating dairy cattle.

Tetracycline

• Bacteriostatic - binds to bacterial ribosomes, preventing transfer RNA from linking.
• Inhibits bacterial cellular function and division.
• Used for many years, significant resistance.
• Bacteria actively take up tetracycline and concentrate it in the cell.
  • Benefits from absorption are improved penetration of tissues.
• Gram positives, gram negatives, rickettsial diseases.
• Concerns: Variable absorption, older forms are hydrophilic, newer are lipophilic, they chelate.
  • Avoid in animals 4-16 weeks old, because it binds to developing tooth enamel.

Aminoglycosides Considerations

• Specific aminoglycosides like gentamycin is the most nephrotoxic, thus urine monitoring for casts is important.
• Longer intervals between doses may reduce toxic blood levels.

Rifamycins Considerations

• Resistant to rifamycin may develop rapidly in a one-step process, so it is often used in combinations.
  • Gram-positive: mycobacteria
  • Gram-negative: chlamydia
  • Anaerobes
• Several viruses (@high concentrations).
  • Red-orange colored urine, tears and saliva (+ sweat) in horses.

Aminocyclitols Considerations

• Lincosamides and Macrolides are bacteriostatic or bactericidal, depending on the substance.
• Good for bacteria resistant to penicillins and cephalosporins, and works on anaerobes.