1. COMMON THERAPEUTICS IN SHEEP
Fouad Kasim Mohammad
Department of Physiology, College of Veterinary Medicine, University of Mosul, Iraq
March 2008

2. PRINCIPLES OF ANTIMICROBIAL THERAPY IN SHEEP
Antibiotic
A substance produced by a microorganism that, at therapeutic doses, inhibits or kills other microorganisms.
Bacteriostatic activity
Stops multiplication of the bacteria (no killing).
All antibiotics are bacteriostatic at some concentrations.
Some are bacteriostatic at almost all concentrations, e.g. sulfonamides, tetracyclines.
Bactericidal activity
Killing the bacteria, when the concentration of the antibiotic is high enough
March 2008

3. Antimicrobial activity may be:
1. Concentration dependent
(aminoglycosides)
2. Concentration and time
dependent (fluoroquinolones)
3. Time dependent (beta lactams).
March 2008

4. General Mechanisms of Action of Antimicrobial Agents
penicillins, cephalosporins, bacitracin, vancomycin.
Inhibition of Cell wall synthesis
chloramphenicol, tetracyclines, aminoglycosides, macrolides, lincosamides,
Inhibition of Protein synthesis
polymyxin, aminoglycosides, amphotericin
Effects on Cell membrane
nitroimidazoles, nitrofurans, quinolones, rifampin (some antiviral agents)
Effects on Nucleic acid function
sulfonamides, trimethoprim
Effects on Intermediary metabolism
March 2008

5. Activity of Various Antimicrobial Classes
Protozoa
Chlamydia
Rickettsia
Mycoplasma
Bacteria +
Aminoglycosides
Beta-lactams
Chloramphenicol
Lincosamides
Macrolides
Pleuromutilins
Tetracyclines
Quinolones
Sulfonamides
Trimethoprim
March 2008

6. Examples of Antibacterial Agents and Their Spectrum of Activity
Anaerobic
Aerobic
G (-)
G (+)
Examples +
chloramphenicol, tetracyclines
Broad
benzyl penicillin G
Narrow
aminoglycosides, sulfonamides, enrofloxacin
carbenicillin, cephalosporins
Intermediate
ampicillin, amoxicillin
March 2008

7. Antibacterial combinations and interactions
Additive (2+3=5).
Synergistic (1+2=8).
(trimethoprim-sulfonamide)
(ampicillin - clavulanic acid)
(erythromycin - rifampin)
(beta-lactam -aminoglycoside)
Antagonistic (3+4=2)
March 2008

8. Antibacterial combinations and interactions
In general,
combining two bacteriostatic drugs
results in additive effect, combining
two cidal drugs results in synergistic
effect. Combining cidal and static
agents can result in impairment of
bacteriocidal activity.
March 2008

9. Therapeutic considerations
Define the anatomical location and severity of the infective process.
The systemic inflammatory response is the presence of two or more of:
High rectal temperature
High heart rate
High respiratory rate
Increased WBC count
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10. Therapeutic considerations
Dose
Determine the correct dose and interval for the drug, the patient, and the condition.
Host immunity
In case of reduced host immunity select a bacteriocidal agent.
March 2008

11. Therapeutic considerations
Short duration may lead to therapeutic failure and re-appearance of infection.
Long duration may increase the risk of adverse drug reactions and may increase resistance in bacterial populations.
Treat 3 days after the end of clinical signs. Some recommend a negative culture before antimicrobial therapy is discontinued.
March 2008

12. ANTHELMINTICS Ideal anthelmintics
Broad spectrum of activity.
Non toxic to treated animals
Wide margin of safety..
Rapid metabolism and excretion
No residues in milk or meat
Easy administration
Cost effective
March 2008

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14. Macrocyclic Lactones (Macrolides)
Ivermectin Eprinomectin Doramectin Moxidectin Milbemycin oxime Selamectin
Bind to chlorine channels causing paralysis
March 2008

15. Benzimidazoles
Thiabendazole Mebendazole Fenbendazole Oxfendazole Oxibendazole Albendazole
Interfere with energy metabolism by inhibition of polymerization of microtubules
March 2008

16. Tetramisole Levamisole Cholinergic agonists
Imidazothiazoles
Tetramisole Levamisole
Cholinergic agonists
March 2008

17. Routes of administration
Oral (suspension, feed mix)
Injection (SC)
Topical (pour on)
Slow release (intraruminal sustained release devices)
March 2008

18. Intraruminal sustained release devices
They allow a slow release of active
drug over a period of time, usually
the complete grazing season. The
aim is to prevent establishment of
nematode populations in hosts
during periods of maximum
availability of third stage infective
larvae.
March 2008

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