Principles of antimicrobial therapy
- Before commencing antimicrobial therapy a few important questions should be answered:
- Is an antimicrobial agent really required?
- Antimicrobial therapy should not be used indiscriminantly.
- Which microorganisms are likely involved?
- Appropriate sample.
- Gram stain to guide therapy while awaiting culture results.
- Culture: specify type of culture (aerobic, anaerobic, mycobacteria) at time of sample submission.
- Susceptibility testing: essential for unpredictable bacteria such as Gram negative bacteria ( Proteus species Proteus spp , Escherichia coli Escherichia coli and especially Pseudomonas species Pseudomonas spp )
- Which antimicrobial agent is suitable?
- Spectrum of activity (as narrow as possible preferable to broad).
- Infection site environment (pH, barriers to therapy, eg specific cellular transport mechanism, cellular debris, abscess walls).
- Route of administration.
- Duration of treatment.
- Safety.
- Legal considerations: whenever possible, a product approved for the indication in that species should be prescribed.
- Other considerations:
Oral and dental infections
Spectrum of bacteria involved
- Gram negative anaerobes ( Bacteroides, Fusobacterium, Porphyromonas).
- Gram positive aerobes (staphylococci Staphylococcus spp , streptococci Streptococcus spp ).
- Actinomyces Actinomyces pyogenes Actinomyces viscosus .
The American Veterinary Dental College only endorses the use of systemic antibiotics prior to oral surgery and dental procedures in "animals that are immune compromised, have underlying systemic disease (such as clinically-evident cardiac, hepatic, and renal diseases) and/or when severe oral infection is present."
Recommended antimicrobials
Bacterial rhinitis Rhinitis
- Rarely a primary entity.
- Nasal swab cultures are low yield - often reflect normal commensal flora.
- Avoid repeated rounds of different antibiotics.
- Look for underling cause and address that (foreign body, Aspergillosis in dogs, Cryptococcus spp Cryptococcus neoformans in cats, prior viral damage to nasal epithelium, neoplasia, allergic rhinitis).
Bordetella bronchiseptica infection Bordetella bronchiseptica infection
Spectrum of bacteria involved
Recommended antimicrobials
- Tetracycline Tetracycline (if mature dentition).
- Doxycycline Doxycycline (risk of dental enamel discoloration unclear, but appears to be low)
- Amoxicillin-clavulanate.
Bronchopneumonia
Spectrum of bacteria involved
Recommended antimicrobials
- Amoxicillin-clavulanate.
- Cephalexin Cefalexin .
- Potentiated sulfonamide.
- Culture by tracheal wash if no response to single empirical trial.
Endocarditis Endocarditis
Spectrum of bacteria involved
- Streptococcus, other gram positive cocci (about half of cases with known cause).
- Gram negatives (22% of cases with known cause).
- Bartonella Bartonella (20-28% of cases with known cause; aortic valve especially).
Commonly effective antimicrobials
- Blood culture and sensitivity strongly recommended due to severe nature of disease, long course of treatment required, and negative consequences of choosing wrong antimicrobial.
- Recommended antimicrobials while awaiting cultures and Bartonella titers:
- Cephalexin.
- Amoxicillin-clavulanate.
- For Bartonella vinsonii:
Pyothorax Pyothorax
Spectrum of bacteria involved
- Mixed anaerobic infections most common.
- May also include E. coli(especially in dogs), and Actinomyces or Pasteurella(especially in cats).
- Culture and sensitivity recommended in all cases.
- Recommended antimicrobials while awaiting aerobic and anaerobic culture.
- Metronidazole + ampicillin Ampicillin + fluoroquinolone.
Bacterial cholecystitis
Spectrum of bacteria involved
- E.coli.
- Enterococcus.
- Anaerobes.
Recommend culture of bile whenever possible (ultrasound guided or at laparotomy)
- Consider combination therapy with:
- Amoxicillin-clavulanic acid + fluoroquinolone.
- Clindamycin + fluoroquinolone.
- Metronidazole + fluoroquinolone.
Cystitis Cystitis: bacterial
Spectrum of bacteria involved
- E. coli, staphylococci, Proteus, Klebsiella.
Recommended antimicrobials
- Tailor therapy based on gram stain of urine:
- Gram positive:
- Amoxicillin, amoxicillin-clavulanic acid, cefadroxil Cefadroxil or cephalexin.
- Gram negative:
- Potentiated sulfonamide or fluoroquinolone.
Leptospirosis
Spectrum of bacteria involved
Recommended antimicrobials
- To eliminate leptospiremia:
- To eliminate the renal carrier state of leptospirosis:
- Renal and/or hepatic failure should be treated with fluid therapy and other supportive measures to maintain normal fluid, electrolyte, and acid-base balance.
Prostatitis Prostate gland: disease
Spectrum of bacteria involved
- E. coli, Klebsiella, Proteus, Pseudomonas.
- Staphylococci, streptococci.
- Mycoplasma, Ureaplasma Mycoplasma and Ureaplasma (opportunistic).
Recommended antimicrobials
- Fluoroquinolone.
- Potentiated sulfonamide.
- Doxycline (for Brucella).
- Chloramphenicol Chloramphenicol .
- Culture and sensitivity essential if no response to single empirical trial.
Pyometra Pyometra
- Secondary bacterial infection may be present.
Spectrum of bacteria involved
- E. coli predominates.
- Ovariohysterectomy Ovariohysterectomy is treatment of choice, following appropriate fluid therapy.
Recommended antimicrobials
- Ampicillin.
- Potentiated sulfonamide.
- Fluoroquinolone.
Pyoderma Bacterial skin disease: overview
Spectrum of bacteria involved
Recommended antimicrobials
- Cephalexin or cefadroxil.
- Amoxicillin-clavulanate.
- Potentiated sulfonamide.
- Recommend culture and sensitivity for cases that do not respond as expected, require multiple courses of treatment and/or have cytological or other evidence that non-staphylococcal bacteria are involved.
Diskospondylitis Diskospondylitis
Spectrum of bacteria involved
- Staphylococci, Streptococcus.
- Brucella.
- E.coli.
- Recommended antimicrobials while awaiting blood and Brucellatiter:
- Doxycycline (if Brucella suspected).
- When no response to antibiotic therapy is seen, or when recurrence is a problem, surgical biopsy, bacterial culture, and antibiotic sensitivity testing are needed.