GI antibiotics

Appendicitis

Coverage should extend to E. coli, Klebsiella, Proteus, and Bacteroides (an anaerobe)

Adult Simple Appendicitis

Antibiotic prophylaxis should be coordinated with surgical consult

Options:

• Cefoxitin 2g IV q6 hours OR
• Cefotetan 2g IV q12 hours OR
• Moxifloxacin 400mg IV once daily OR
• Ertapenem 1g IV once daily

Pediatric Simple Appendicitis

Options:

• Cefoxitin 40mg/kg IV q6 hours
• Cefotetan 40mg/kg IV q12 hours
• Gentamicin 2.5mg/kg IV q8hrs +
  • Metronidazole 7.5mg/kg IV q6hrs OR
  • Clindamycin 10mg/kg IV q8hrs
• Ertapenem 15mg/kg IV q12h (max 1g); >13 years: 1g IV daily

Adult Complicated Appendicitis

Defined as perforation, abscess, or phlegmon

Options:

• Metronidazole 500mg IV q8hrs +
  • Cefepime 2g IV q12hrs OR
  • Ciprofloxacin 400mg IV q12hrs OR
  • Levofloxacin 750mg IV q24hrs OR
  • Aztreonam 2g IV q8hrs
• Imipenem/Cilastatin 500mg IV q6hrs
• Meropenem 1g IV q8hrs
• Piperacillin/Tazobactam 4.5g IV q8hrs

Pediatric Complicated Appendicitis

Options:

• Metronidazole 7.5mg/kg IV q6hrs +
  • Cefepime 50mg/kg IV q12hrs (max 2g) OR
  • Aztreonam 30mg/kg IV q8hrs
• Imipenem/Cilastatin 25mg/kg IV q6hrs (max 500mg)
• Meropenem 20mg/kg IV q8hrs (max 1g)
• Piperacillin/Tazobactam 100mg/kg IV q8hrs (max 4.5g)

Cautious use should be applied to use of fluoroquinolones in complicated pediatric appendicitis due to the risk of tendon injury

Cholecystitis

Most often isolated organisms are Escherichia coli, Klebsiella pneumonia, and anaerobes, especially Bacteroides fragilis

Uncomplicated

Pathogenicity of Enterococci remains unclear and specific coverage is not routinely suggested for community-acquired infections

• Ertapenem 1g IV once daily OR
• Metronidazole 500mg IV q8hrs PLUS
  • Ciprofloxacin 400mg IV q12 hrs OR
  • Levofloxacin 750mg IV q24hrs OR
  • Ceftriaxone 1g IV q24hrs

Complicated or Healthcare Associated

Examples of complication include severe sepsis or hemodynamic instability

• Vancomycin 15-20mg/kg PLUS any of the following options

Options:

• Metronidazole 500mg IV q8hrs PLUS Ciprofloxacin 400mg IV q12hrs
• Piperacillin/Tazobactam 4.5g IV q8hrs
• Imipenem/Cilastatin 500mg IV q6hrs
• Doripenem 500mg IV q8hrs
• Meropenem 1g IV q8hrs

Pediatric

• Ceftriaxone 50-75mg/kg IV daily (max 2g) + Metronidazole 7.5mg/kg IV q8hrs (max 500mg) OR
• Piperacillin/Tazobactam 80-100mg/kg IV q6-8hrs (max 4.5g) OR
• Meropenem 20mg/kg IV q8hrs (max 1g)

Clostridium Difficile

Mild/Moderate Infection

• Vancomycin 125 mg PO four times daily for 10 days
• Fidaxomicin 200 mg PO two times daily for 10 days
• Metronidazole 500mg PO or IV three times daily for 10 days (third line therapy)

Pediatric:

• Vancomycin 10mg/kg PO QID x 10 days (max 125mg/dose)
• Fidaxomicin 200mg PO BID x 10 days (>12yr and >40kg); weight-based for younger
• Metronidazole 7.5mg/kg PO/IV TID x 10 days (max 500mg/dose) (third line)

Serious Infection

• Vancomycin 125 mg PO four times daily for 10 days
• Fidaxomicin 200 mg PO two times daily for 10 days

Diverticulitis

Uncomplicated

First, consider whether antibiotics are needed:

• In immunocompetent patients with mild uncomplicated diverticulitis (no systemic signs, able to tolerate PO, reliable follow-up), a trial of supportive care alone (bowel rest, hydration, pain control) without antibiotics is reasonable
• Antibiotics ARE indicated if: immunocompromised, significant comorbidities/frailty, CRP >140 mg/L, WBC >15 × 10⁹/L, refractory symptoms, vomiting, or CT showing fluid collection or longer segment of inflammation

If antibiotics are prescribed (4-7 day course preferred):

Preferred:

• Amoxicillin/Clavulanate 875/125mg PO Q8hrs x 5 days (or Augmentin XR 2 tablets BID [each tablet 1gm amoxicillin 62.5mg clavulanate])
  • Equally effective as fluoroquinolone + metronidazole with lower C. difficile risk (especially in patients ≥65 years)
  • Avoids FDA black box fluoroquinolone risks (tendinopathy, neuropathy, aortic dissection, CNS effects)

Alternatives (penicillin allergy or intolerance):

• Trimethoprim/Sulfamethoxazole one double-strength tablet BID PLUS Metronidazole 500mg PO Q8h x 5 days
• Metronidazole 500mg PO Q8hrs PLUS Ciprofloxacin 500mg PO BID x 5 days (reserve for patients without non-fluoroquinolone options)
• Moxifloxacin 400mg PO QDaily (same fluoroquinolone cautions apply)

Complicated

Options:

• Ticarcillin/Clavulanate 3.1 g IV Q6h or
• Piperacillin/Tazobactam 3.375 g IV q6 hours x 7-10 days
• Ciprofloxacin 400 mg IV q12h and Metronidazole 1 g IV Q12h
• Ampicillin 2 g IV Q6h and Metronidazole 500 mg IV q6h Plus (Gentamicin 7 mg/kg Q24h or Ciprofloxacin 400 mg IV Q12h)
• Imipenem/Cilastatin 500 mg IV Q6h

General Sick

Intra-Abdominal Sepsis/Peritonitis

	Harbor-UCLA	Santa Monica-UCLA	Other
Primary	Metronidazole 500mg IV q8hrs Plus one of the following: Ceftriaxone 1g IV once daily Ciprofloxacin 400mg IV q12hrs Cefazolin 1g (30mg/kg) IV q8hrs Levofloxacin 750mg IV once daily	Metronidazole 500mg IV q8h + Vancomycin 15mg/kg/dose IV q12h (Max dose = 1500mg) Plus one of the following: Piperacillin/tazobactam 4.5g IV q6h Ertapenem 1g IV q24h Ceftriaxone 1g IV q24h	One of the following: Piperacillin-tazobactam Ticarcillin-clavulanate 3.1 g IV every 6 hours Ertapenem 1 g every 24 hours Moxifloxacin 400 mg IV every 24 hours
Allergy or prior exposure	Piperacillin/Tazobactam 4.5g (80mg/kg) IV q8hrs OR Metronidazole 500mg IV q8hrs PLUS Cefepime 2g IV once daily OR Ciprofloxacin 400mg IV q12hrs OR Levofloxacin 750mg IV once daily Meropenem 1g (20mg/kg) IV q8hrs OR Doripenem 500mg IV q8hrs OR Aztreonam 2g (30mg/kg) IV q8hrs + Metronidazole 500mg IV q8hrs	aztreonam 2g IV q8h + metronidazole 500mg IV q8h +/- vancomycin 15mg/kg/dose IV q12h (Max dose = 1500mg)

Pediatric

• Metronidazole 7.5mg/kg IV q8hrs (max 500mg) + one of:
  • Ceftriaxone 50-75mg/kg IV daily (max 2g) OR
  • Cefotaxime 50mg/kg IV q8hrs (max 2g/dose)
• Piperacillin/Tazobactam 80-100mg/kg IV q6-8hrs (max 4.5g) OR
• Meropenem 20mg/kg IV q8hrs (max 1g)

Infectious Diarrhea

Campylobacter jejuni

• Erythromycin 500mg PO BID x 5 days
• Ciprofloxacin 500mg PO BID x 5 days OR
• Azithromycin 500mg PO once daily x 5 days

Pediatric:

• Azithromycin 10mg/kg PO daily x 3 days (max 500mg)
• Erythromycin 10mg/kg PO QID x 5 days (max 500mg/dose)

Entamoeba Histolytica

• Metronidazole 750mg PO three times daily for 5-10 days PLUS
  • Paromomycin 500mg q8hrs for 7 days OR
  • Iodoquinol 650mg q 8hrs daily 20 days

Giardia lamblia

• Metronidazole 250mg PO q8hrs for 7-10days
• Tinidazole 2g PO once

Microsporidium

• Albendazole 400mg PO BID x 21 days + HAART therapy if HIV positive

Cryptosporidium

• Paromomycin 500mg PO q8hrs x 14-28days +HAART therapy if HIV positive

Salmonella (non typhoid)

• Treatment is not recommended routinely but should be considered if:
• Immunocompromised
• Age<6 mo or >50yo
• Has any prostheses
• Valvular heart disease
• Severe Atherosclerosis
• Active Malignancy
• Uremic

Options: Immunocompromised patients should have 14 days of therapy

• TMP/SMX 1 DS tab PO BID x 5 days
• Ceftriaxone 2g IV once daily x 5 days
• Levofloxacin 500mg PO once daily x 5 days
• Ciprofloxacin 500mg PO BID x 5 days

Pediatric:

• Treatment recommended if age <6 months, immunocompromised, or bacteremia
• Ceftriaxone 50-75mg/kg IV daily x 5 days (max 2g)
• TMP/SMX 8mg/kg/day (TMP) PO divided BID x 5 days
• Azithromycin 10mg/kg PO day 1, then 5mg/kg/day x 4 days

Shigella

Treatment extended for 10 days if immunocompromised'

• Ciprofloxacin 500mg PO BID x 5 days
• TMP/SMX 1 DS tab PO BID x 5 days
• Levofloxacin 500mg PO once daily x 5 days
• Azithromycin 500mg PO daily x 5 days

Pediatric:

• Azithromycin 10mg/kg PO day 1 (max 500mg), then 5mg/kg/day x 4 days
• Ceftriaxone 50mg/kg IM/IV daily x 5 days (max 2g)
• TMP/SMX 8mg/kg/day (TMP) PO divided BID x 5 days (if susceptible)

Vibrio Cholerae

• Doxycycline 300mg PO as single dose
• TMP/SMX 1 tablet (5mg/kg) PO BID daily x 3 daily
• Azithromycin 20mg/kg (1g) PO once

Yersinia enterocolitica

Antibiotics are not required unless patient is immunocompromised or systemically ill

• Ciprofloxacin 500mg PO BID daily
• Levofloxacin 500mg PO once daily
• TMP/SMX 1 DS tab (5mg/kg) PO BID

Peritoneal Dialysis Associated Peritonitis

Empiric Therapy (IP)

10- to 14-day course of intraperitoneal (IP) antibiotics that are administered by the patient on an outpatient basis or IV antibiotics and intraperitoneal for admitted patients

• Vancomycin 30mg/kg loading followed by 0.6 mg/kg IP daily PLUS
• Ceftazidime 1g IP daily OR
• Gentamicin 0.6mg/kg daily
• Catheter removal/exchange is usually only done if IP antibiotics fail (fungal, pseudomonal), and should be done in consultation with a nephrologist

Empiric Tharapy (IV)

Although IP antibiotics are preferred IV antibiotics can be considered with coordination with nephrology for dosing. Coverage should be the same as IP antibiotics

Traveler's Diarrhea

Options for Adults:

• Ciprofloxacin 750mg PO once daily x 1-3 days
  • First choice for use except in South and Southeast Asia
• Azithromycin 500mg PO q24h x 3 days OR 1000mg PO x 1
  • Nausea is a frequent adverse event
  • First choice for use in South and Southeast Asia
• Rifaximin 200mg PO TID x 3 days
  • Ineffective against mucosally invasive pathogens (Shigella, Salmonella, Campylobacter)
  • Considered very safe as it is not absorbed

Typhoid Fever

Oral therapy with Quinolone Susceptibility

• Ciprofloxacin 500-750 mg PO q 12 hrs x 14 days

Parenteral Therapy with Quinolone Susceptibility

• Ciprofloxacin 400 mg IV q 12 hrs x 10 days

Parenteral Therapy with Quinolone Resistance

if nalidixic acid resistant, assume fluoroquinolone resistant

• Ceftriaxone 2g IV q 24 hrs x 14 days

OR

• Cefixime 10-15 mg/kg IV q 12 hrs x 8 days

Oral Therapy with Quinolone Resistance

• Azithromycin 1 g PO daily x 5 days
• Amoxicillin Not 1st line treatment; 50-100mg/kg/day PO divided q6-8h x 14 days; First Dose: 12.5mg-33.3mg/kg PO x 1
• Amoxicillin Not 1st line treatment; 50-100mg/kg/day PO divided q6-8h x 14 days

Pediatric

• Ceftriaxone 50-80mg/kg IV daily x 10-14 days (max 2g)
• Azithromycin 10-20mg/kg PO daily x 5-7 days (max 1g)
• Cefixime 15-20mg/kg/day PO divided BID x 7-14 days (max 400mg/dose)

See Also

Antibiotics by diagnosis

• Bone and joint antibiotics
• Cardiovascular antibiotics
• ENT antibiotics
• Eye antibiotics
• GI antibiotics
• GU antibiotics
• Neuro antibiotics
• OB/GYN antibiotics
• Pulmonary antibiotics
• Skin and soft tissue antibiotics
• Bioterrorism antibiotics
• Environmental exposure antibiotics
• Immunocompromised antibiotics
• Post exposure prophylaxis antibiotics
• Pediatric antibiotics
• Sepsis antibiotics
• Arthropod and parasitic antibiotics

For antibiotics by organism see Microbiology (Main)