Appendicitis Organism-Specific Therapy 

Treatment regimens are included below for the most common isolates associated with acute appendicitis. Guideline-directed therapy focuses on the empiric treatment of these organisms, which includes Escherichia coli and other coliforms, anaerobes, and gram-positive cocci. Thus, organism-specific therapeutic regimens for appendicitis include coverage for anaerobic organisms (including Bacteroides fragilis, Clostridium spp, and Prevotella spp), aerobic gram-negative bacilli (including E coli, Klebsiella spp, and Proteus mirabilis), Pseudomonas aeruginosa, streptococci, enterococci, and mixtures of aerobes and anaerobes. ^{[1, 2, 3, 4]}

A single-drug, broad-spectrum antibiotic such as piperacillin-tazobactam or multidrug regimens may be initially necessary to achieve wide-spectrum coverage of multiple organisms. Later, therapy can be further narrowed on the basis of sensitivities if microbiology culture data become available to the healthcare provider. ^[4]    

See Appendicitis: Avoiding Pitfalls in Diagnosis, a Critical Images slideshow, to help make an accurate diagnosis.

Anaerobic organisms (including Bacteroides fragilis, Clostridium spp, Prevotella spp, Peptostreptococcus spp)

Lincomycins

• Clindamycin 600 mg IV q8h or

Nitroimidazoles

• Metronidazole 500 mg IV q8h or

Carbapenems

• Ertapenem 1 g IV q24h or

Penicillin/beta lactamase

• Ampicillin-sulbactam 3 g IV q6h or

• Ticarcillin-clavulanate 3.1 g IV q4-6h or

Combination cephalosporin/beta lactamase/nitroimidazole

• Ceftolozane/tazobactam 1.5 g IV q8h plus metronidazole 500 mg IV q8h

Facultative aerobic gram-negative bacilli (including E coli, Klebsiella spp, P mirabilis)

Carbapenems

• Aztreonam 1-2 g IV q6-8h or

• Ertapenem 1 g IV q24h or

Penicillins

• Ampicillin 2 g IV q4h or

Fluoroquinolones

• Ciprofloxacin 400 mg IV q12h or

• Levofloxacin 750 mg IV q24h or

Cephalosporins

• Cefoxitin 2g IV q8h or

• Cefotetan 2 g IV q12h or

• Cefotaxime 1-2 g IV q6-8h or

• Ceftriaxone 1-2g IV q24h or

Combination cephalosporin/beta lactamase/nitroimidazole

• Ceftolozane/tazobactam1.5 g IV q8h plus  metronidazole 500 mg IV q8h or

Lincomycins

• Gentamicin 5-7 mg/kg IV q24h     

Pseudomonas aeruginosa

Carbapenems

• Aztreonam 1-2 g IV q8h or

• Meropenem 1 g IV q8h or

• Doripenem 500 mg IV q8h or

Fluoroquinolones

• Ciprofloxacin 400 mg IV q12h or

Beta lactamase

• Piperacillin-tazobactam 4.5 g IV q6h or

Carbapenem/dehydropeptidase inhibitor

• Imipenem-cilastatin 500 mg IV q6h or

Combination cephalosporin/beta lactamase/nitroimidazole

• Ceftolozane/tazobactam1.5 g IV q8h plus metronidazole 500 mg IV q8h

Streptococci and enterococci

Penicillin/beta lactamase

• Ampicillin-sulbactam 3 g IV q6h or

• Ticarcillin-clavulanate 3.1 g IV q4-6h or

Beta lactamase

• Piperacillin-tazobactam 3.375-4.5 g IV q6-8h or

Carbapenems

• Doripenem 500 mg IV q8h or

• Meropenem 1 g IV q8h or

Carbapenem/dehydropeptidase inhibitor

• Imipenem-cilastatin 500 mg IV q6h or

Combination cephalosporin/beta lactamase/nitroimidazole

• Ceftolozane/tazobactam 1.5 g IV q8h plus metronidazole 500 mg IV q8h

Mixed flora: aerobes and anaerobes

Cephalosporins

• Cefoxitin 2g IV q8h or

• Cefotetan 2 g IV q12h or

Beta lactamase

• Piperacillin-tazobactam 3.375-4.5 g IV q6h or

Penicillin/beta lactamase

• Ampicillin-sulbactam 3 g IV q6h or

• Ticarcillin-clavulanate 3.1 g IV q4-6h or

Fluoroquinolones

• Moxifloxacin 400 mg IV q24h or

Carbapenems

• Doripenem 500 mg IV q8h or

• Meropenem 1 g IV q8h or

• Ertapenem 1 g IV daily or

Carbapenem/dehydropeptidase inhibitor

• Imipenem-cilastatin 500 mg IV q6h