Diarrhea

at the bedside

airway, breathing, circulation; full vitals, glucose; IV access if dry or unwell
how dry → mucosa, capillary refill, postural drop, urine output
C. difficile risk → antibiotics or hospital in the last 3 months, PPI, age: isolate and send the stool before the result
frail or immobile after days without stool → rectal exam first, it may be overflow

escalate now if

hypotension or tachycardia not correcting with fluids → hypotension, fluids
fever > 38.5 °C with bloody stool → infectious colitis, C. difficile
severe pain, distension or peritonism → toxic megacolon, ischemic colitis, surgery now → abdominal pain
WBC ≥ 15, creatinine rising, or ileus with C. difficile → severe or fulminant C. difficile
confusion or acidosis → sepsis or severe dehydration → fever, venous blood gas
K⁺ < 3.0 or AKI → potassium, acute kidney injury

C. difficile → recent antibiotics or hospital stay, watery stool, cramps, raised WBC
infectious colitis → fever, blood, travel, outbreak, food; Salmonella, Shigella, Campylobacter, E. coli
viral gastroenteritis → vomiting first, watery, self-limited, sick contacts
drugs and feeds → laxatives, antibiotics, PPI, metformin, colchicine, enteral feeds
overflow → impaction with leakage → constipation
IBD flare, ischemic colitis → blood, known IBD; sudden pain then bloody stool in a vascular patient
immunocompromised → CMV, Cryptosporidium, Giardia: lower threshold to investigate

stool → onset, frequency, volume; watery, fatty or bloody; nocturnal
symptoms → fever, vomiting, pain, distension, urine output
history → antibiotics or hospital in the last 3 months, IBD, immunosuppression, recent surgery, travel, food, sick contacts
drug chart → laxatives, PPI, metformin, antibiotics, enteral feed rate
exam → hydration; distension, tenderness, peritonism; bowel sounds; rectal exam if impaction or blood

uncomplicated watery diarrhea needs no bloods and no stool tests
CBC, RFT, Mg → dehydrated, unwell, or any escalate feature; VBG, lactate → if unwell
C. difficile test → unformed stool only, with a reason to suspect it (antibiotics or hospital, ≥ 3 unformed stools in 24 h); per the lab algorithm; never formed stool, never a test of cure
stool culture → bloody stool, fever, travel, outbreak, immunocompromised; ova and parasites → travel or > 7 days
calprotectin → suspected IBD flare only; abdominal X-ray or CT → distension, peritonism, severe C. difficile

every patient

oral rehydration if drinking; IV balanced crystalloid 500 mL boluses if dry, then maintenance; replace K and Mg
stool chart, strict input and output; stop laxatives and offending drugs
loperamide 4 mg then 2 mg per loose stool (max 16 mg/day) → only for watery diarrhea without fever or blood; never in C. difficile or bloody diarrhea

C. difficile

isolate, contact precautions, soap and water; stop the offending antibiotic and the PPI if possible
first episode → fidaxomicin 200 mg PO BD × 10 d (preferred) or vancomycin 125 mg PO QID × 10 d; the same drugs for severe disease (WBC ≥ 15 or creatinine > 1.5 mg/dL)
fulminant (hypotension, ileus, megacolon) → vancomycin 500 mg PO/NG QDS + metronidazole 500 mg IV q8h; add vancomycin PR if ileus; surgery and ICU now
full regimens and recurrence → empiric antibiotics

infectious colitis

most acute diarrhea needs no antibiotic; they prolong shedding and select resistance
antibiotics → bloody diarrhea with fever or severe illness, immunocompromised, suspected sepsis or enteric fever, outbreak → empiric antibiotics
viral → fluids only; parasites → targeted once identified

other

IBD flare → fluids, stool culture and C. difficile first, GI for steroids; bloody diarrhea not improving in 48–72 h → GI
overflow → disimpaction and laxatives, no antidiarrheal → constipation
enteral feeds → slow the rate, check the formula, do not stop feeding reflexively

shock persists → hypotension, advanced: shock
hand over → stool chart, fluids and electrolytes, C. difficile sent or not, isolation, review time

source	type
IDSA/SHEA 2021 C. difficile guideline	international guideline
IDSA 2017 infectious diarrhea guideline	international guideline

Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.

free the on-call checklist covers the whole shift on one printable page.

studying for the IM exam? the IM Rapid Review covers this in the same format. see the sample chapter.

reviewed Jul 2026updated Oct 2026file complaint/diarrhea