Adult Outpatients: Gastrointestinal Infections: Diarrhea


Doses provided in this table are for patients with normal renal and hepatic function. Click on drug link to go to dosing guidelines.  Some antimicrobials are restricted (ID-R).  Click on link for guidelines on obtaining authorization.


Common Pathogens

Drug(s) of First Choice


Dysenteric Diarrhea

Frequent, sometimes bloody, small-volume diarrhea associated with abdominal pain and cramping.

Patient may be febrile and toxic.






E. coli 0157:H7


Ciprofloxacin 500 mg PO BID


Ciprofloxacin 750 mg daily x 3 days


(avoid in cases of E. coli O157:H7 as it may increase the risk of hemolytic-uremic syndrome)


Recent antibiotic exposure: consider C. difficile

Antimotility drugs should not be used in C.difficile.

C. difficile - Metronidazole 500 mg PO TID x 10-14 days. If no response at 5 days, switch to Vancomycin 125mg PO QID x10-14 days. See inpatient guidelines for severe or recurrent C. difficile infection and/or policy on C. difficile management.

Empiric therapy is generally indicated if patient is toxic appearing, elderly or immunocompromised.  If empiric therapy is given, obtain culture and give fluoroquinolone x 3 days while awaiting cultures.


Azithromycin should be used for pregnancy and suspected quinolone resistant Campylobacter.


Antimotility drugs improve symptoms and can be used if patient is not toxic.  

Strict handwashing is mandatory in all food preparation.

Antimicrobial treatment may worsen outcomes in patients with E. coli 0157:H7

E. histolytica - Metronidazole 750 mg PO TID x 7-10 days then Iodoquinol 650 mg PO TID x 20 days or Paromomycin25-35 mg/kg/day in 3 divided doses x 7 days

Nondysenteric Diarrhea

Large volume, nonbloody, watery diarrhea.

Patient may have nausea, vomiting, and abdominal cramping but fever often absent.



Enterotoxigenic E. coli

Enterotoxin-producing bacteria

General Care: Observation

Oral rehydration

Antimotility agents


Giardia – especially if patient describes recent history of travel and/or ingestion of unfiltered water (e.g., camping), consider – Metronidazole 250 mg PO TID x 5 days. 

Generally, empiric therapy and stool cultures are not indicated. Most disease is self-limiting and can be treated with antimotility agents.

If patient fails to improve, cultures (-), and symptoms persist, consider stool for O & P.

Metronidazole resistance seen in 20% giardia cases.

Check C. difficile toxin if recent history of antibiotic use or hospitalization. 

Traveler’s diarrhea

Empiric treatment while abroad

Toxigenic E. coli





Ciprofloxacin 500 mg PO BID x 1-3 days


Pregnancy or fluoroquinolone-resistant campylobacter:

Azithromycin 1 g x 1 dose


Loperamide 4 mg PO x 1; then 2 mg after each loose stool,

MAX 16 mg/day

Mild, self-limited cases can be treated with fluid and electrolyte repletion and bismuth subsalicylate.

Prophylaxis generally not recommended.