Antimicrobials

Question 1

Beta-lactams - Penicillin’s

Answer 1

• Inhibit cell wall synthesis by blocking bacterial enzymes essential for building the bacterial cell wall
• Bactericidal

Includes:
1. Penicillin’s (Narrow, G+) - Procaine penicillin, benzylpenicillin G, penicillin V
2. Aminopenicillin’s (Broad, G+ & G-) - ampicillin, amoxicillin
3. Antipseudomonas penicillin (Enhanced activity against G- & anaerobes) - ticarcillin & piperacillin
4. Augmented penicillin - Amoxicillin/ clavulanic acid & ticarcillin/ clavulanic acid

Toxicity:
- Low systemic toxicity, as mammalian cells do not possess a bacterial cell wall.
- Major toxicity is vomiting and diarrhea.
- Hypersensitivity reactions

Distribution:
USE: ECF, body fluids, placenta
DONT USE: abscess, bone, eye, CSF, milk

Prohibited:
- Never give to guinea pigs, ferrets, rabbits, or hamsters by any route.
- Oral penicillins should not be used in adult horses
- Adverse effects may be due to toxic effects of potassium or procaine.

Question 2

Other Beta-lactams (Cephalosporins, Carbapenems & Monobactams)

Answer 2

Cephalosporins
- 4 generations
- 1st generation best activity against G +
- 2nd, 3rd, and 4th generations are more effective against G -

Distribution: ESF & Bone

Toxicity: Hypersensitivity reactions & GIT upsets

Carbapenems
- Human drug, wide antimicrobial activity, only for serious infections

Monobactams
- Gram-negative bacteria only

Question 3

Aminoglycosides & aminocyclitols

Answer 3

• Inhibition of protein synthesis
• Inactive against anaerobes or in an anaerobic environment
• Inactive in acidic urine, pus, or necrotic debris
• Bactericidal

Includes: gentamicin, neomycin, streptomycin, kanamycin, apramycin, and amikacin.

Distribution:
- Use ECF (synovial, perilymph, pleural, pericardial, and peritoneal fluids)
- Not to be used in CSF, ocular fluids, milk, intestinal fluids, or prostatic secretion

Toxicity: Nephrotoxic, ototoxic, neuromuscular junction blockage, cardiac effect, can cross the placenta

Nephrotoxicity can be avoided if gentamicin is:
- Not used for more than 7 days
- Not used in dehydrated animals
- Not used in animals with impaired renal function
- Stopped when toxicity is detected
- Recommended to decrease the dose by 25% in aged animals

Prohibited:
- Neomycin should NOT be used in cats

Question 4

Macrolides

Answer 4

• Inhibition of protein synthesis
• Bacteriostatic or bacteriocidal (functioning immune system required for effect)
• Active against G+, mycoplasma, and anaerobes (not G-)

Includes: erythromycin, clarithromycin, azithromycin, Spiramycin, tylosin, tilmicosin, and tulathromycin

Distribution: Widely in the body; concentrates in the spleen, liver and kidney, lungs, and milk.

Toxicity:
- Vomiting, diarrhea, and colitis (oral dosing)
- Irritant following IM inj.

Prohibited:
- Not used in Horses (adult horses) and small herbivores

Question 5

Lincosamides

Answer 5

• Inhibit protein synthesis
• Bactericidal or bacteriostatic (require a functioning immune system to be effective)
• Active against G+ bacteria, Mycoplasma, and anaerobes (not G-)

Distribution: Most tissues (skin, bone, prostate, milk, CSF)

Toxicity:
- GI toxicity (fatal diarrhea - ruminants, horses, rabbits & guinea pigs)
- Avoided in animals with pre-existing liver or kidney disease.

Question 6

Pleuromutilins

Answer 6

• Inhibits protein synthesis
• Active against G+, anaerobic bacteria, Mycoplasma, spirochaetes

Question 7

Amphenicols

Answer 7

• Inhibit protein synthesis
• Bacteriostatic

Distribution: Most tissues (prostate), eye, BBB, placenta

Question 8

Tetracyclines

Answer 8

• Inhibit protein synthesis
• Bacteriostatic
• Broad spectrum - G+ and G-

Includes: Chlortetracycline, oxytetracycline, tetracycline, doxycycline

Distribution: ECF, bone, placenta, milk

Toxicity:
- GI Upset
- Tissue damage at injection sites
- Do not give rapidly IV - collapse due to hypocalcemia
- Immunosuppressive
- Photosensitivity

Prohibited:
- DO NOT give to pregnant animals and avoid use in young animals (tooth discoloration, inhibited bone development - tetracycline chelates)
- CARE in horses (super infectious)

Question 9

Sulphonamides/trimethoprim

Answer 9

• Inhibition of nucleic acid synthesis
• Sulphonamides - bacteriostatic
  Trimethoprim sulphonamides - bactericidal
• Active against G+, G- and anaerobes
• Antagonized by puss/ necrotic tissue

Distribution:
- ECF , eye, placenta
- CSF (low protein binding sulphadiazine, sulphadiazine)

Toxicity:
- Polyarthritis, fever, cutaneous eruptions, thrombocytopenia, hepatitis.
- Renal effects (ensure animals receiving sulphonamides are well hydrated)
- Keratoconjunctivitis sica (dry eye) dogs
- Cats: excessive salivation if enteric tablet coat broken

Contradictions:
- Dobermans: hypersensitivity (avoid) “black and tan” also Samoyeds and Schnauzers

Question 10

Fluoroquinolones

Question 11

Polymyxins

Question 12

Glycopeptides

Question 13

Bacitracin

Question 14

Streptogramins

Question 15

Prophylaxis

Answer 15

• Preventative Treatment
• Animals may not be sick (i.e. preventative)
• Given prior to onset of clinical signs

Question 16

Metaphylaxis

Answer 16

• Treat whole herd when few cows present with clinical signs
• Treat entire herd who has come into contact
• Control measure to slowdown onset of disease and hopefully alleviate some stress of disease