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

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

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

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

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

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

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

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

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 March 2008

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

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

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

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

Tetramisole Levamisole Cholinergic agonists Imidazothiazoles Tetramisole Levamisole Cholinergic agonists March 2008

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

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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