Surgical Infections and Antibiotic Selection

By: Masoud Salaran DVM, Resident in Veterinary Surgery

Introduction

golden age 1941

Antib

iotic

Prophylactic

therapeutic

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Bacterial survival in a host depends on:

bacterial virulence and numbershost immunocompetencewound factors that deactivate host defenses

presence of blood clots foreign material ischemic tissue pockets of fluid

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Destruction of Bacterial Cell Walls

Inhibition of Protein Synthesis

Inhibition of DNA Synthesis

MECHANISMS OF ANTIBIOTIC ACTION

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β-lactam ring antibiotics Penicillins

Vancomycin Cephalosporins

Bacitracin Carbapenems

Polymyxin Monobactams

Nystatin

Amphotericin B

Imidazoles

Destruction of Bacterial Cell Walls

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Aminopenicillins amoxicillin, ampicillinGram aerobes and some Gram and Gram anaerobes

Carboxypenicillins ticarcillinbetter Gram and anaerobe spectrums than the aminopenicillins

Ureidopenicillins piperacillin, mezlocillinbest Gram spectrums of all the penicillins

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Cephalosporins 7

Bind to bacterial ribosomes, causing reversible inhibition of protein synthesis

Chloramphenicol

Tetracycline

Erythromycin

Clindamycin

Inhibition of Protein Synthesis

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Chloramphenicol:

Broad-spectrum activity against streptococci, staphylococci, Salmonella spp., Brucella spp., Pasteurella spp., Ehrlichia spp., Rickettsia spp., and anaerobes, but it has poor activity against Pseudomonas spp.

Highly lipophilic

Inhibition of Protein Synthesis

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Tetracycline, Oxytetracycline, Doxycycline, Minocycline

Many Gram and Gram bacteria, including Chlamydia spp., Rickettsiae, Spirochetes, Mycoplasma spp., Bacterial L-forms, and some Protozoa

Staphylococci, Enterococci, Pseudomonas spp., and Enterobacteriaceae

Tetracyclines

Doxycycline fewer side effects

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Readily absorbedNarrow spectrum Clarithromycin New derivatives Azithromycin Dirithromycin

Azithromycin

Aerobic bacteria (e.g., Staphylococci, Streptococci, Helicobacter spp.) and anaerobes. Mycoplasma spp., Intracellular organisms (e.g., Bartonella spp. Toxoplasma spp.), and atypical Mycobacteria

Oral absorption of azithromycin is high, and it is well tolerated. The drug achieves extremely high tissue concentrations and needs to be given only once daily

Erythromycin

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LincomycinGram pathogens, including staphylococci, streptococci, clostridia, several Actinomyces spp., and some Nocardia spp.very effective against many anaerobic bacteria. Against Toxoplasma gondii, Neospora, and staphylococcal osteomyelitis but ineffective against Gram bacteria.

often is used to treat infections resistant to penicillins and erythromycin or patients that cannot tolerate those drugs.

Clindamycin

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Effective against Gram and Gram bacteria, including Enterobacteriaceae and pseudomonads, and have a synergistic effect with β-lactam antibiotics but …

Anaerobes Resistant

lipid insoluble but pleural fluid, bone, joints and peritoneal cavity

Dehydration, electrolyte loss, preexisting renal disease, and concurrent use of other nephrotoxic drugs increase nephrotoxicity of aminoglycosides and NSAID

Aminoglycosides

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Enrofloxacin DifloxacinFluoroquinolones Ciprofloxacin Ofloxacin Marbofloxacin

Potentiated sulfas Trimethoprim-sulfa

Inhibition of DNA Synthesis

Fluoroquinolones 15

Trimethoprim-sulfonamid : osteomyelitis, prostatitis, pneumonia, tracheobronchitis, pyoderma, urinary tract infections

Metronidazole

Anaerobic bacteria

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multidrug-resistant (MDR) Infections

Vancomycin, Carbapenems , Oxazolidinone Linezolid , Streptogramin combination of Dalfopristin and Quinupristin , Tigecycline , Lipopeptide Daptomycin , newest Fluoroquinolones Moxifloxacin fourth- and fifth generation Cephalosporins

DRUGS OF LAST RESORT

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Dosages of New or Commonly Used Antibiotics in Veterinary Medicine 18

Inappropriate dose frequency, or route of administrationinadequate length of treatmentinappropriate antibiotic selectionpersistence of the cause of infectionantibiotic resistance

incorrect diagnoses depressed host immunity Pharmacokinetics of the drug drug reactions antibiotic antagonism inability of the antibiotic to reach the target tissue

CAUSES OF FAILURE

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Classification of Surgical Wounds

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Classifications of Surgical Infections

1. with primary surgical disease (e.g., osteomyelitis that occurs secondary to an open fracture, pyometra, peritonitis that occurs secondary to gastrointestinal perforation, or prostatic abscessation)

2. as a complication of a surgical procedure not commonly associated with infection

3. as a complication of support procedures,with

4. prosthetic implants

Prevention of Surgical Infections

Primary objective of aseptic surgery

Factors host factors operating room characteristics of bacterial contaminantsProper atraumatic tissue handling and instrument use are also important in preventing infection

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PROPHYLACTIC USE OF ANTIBIOTICS 23

Antibiotic selectionPrevent or treat infection effective VS at least 80% of probable pathogens

Staphylococcus spp. (especially coagulase-positive S. aureus), E. coli, and Pasteurella spp.

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Antibiotic Selection System involved Cytologic studies Antibiotic reaches target tissue Least expensive, least toxic, and most

convenient to administer Timing of Antibiotic Administration Dose Routes of Antibiotic Administration Duration of Antibiotic Administration

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NOW WHAT ???

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