Diarrhoea
Assessment, oral rehydration, antimotility agents and antibiotic selection per NICE and BNF
Diarrhoea is defined as three or more loose or liquid stools per day. Acute diarrhoea lasting under four weeks is most commonly infectious and self-limiting. Chronic diarrhoea requires systematic investigation to exclude inflammatory bowel disease, coeliac disease, colorectal cancer, and functional causes such as IBS.
Acute Infectious Diarrhoea
Most acute diarrhoea is viral (norovirus, rotavirus) and self-limiting — the cornerstone of management is oral rehydration with oral rehydration salts (Dioralyte). Loperamide 4 mg initially then 2 mg after each loose stool (max 16 mg/day) can reduce stool frequency in non-bloody, afebrile acute diarrhoea — it must not be used in suspected C. difficile or bloody diarrhoea. Antibiotic treatment is only indicated for specific bacterial causes: azithromycin 500 mg once daily for 3 days for Campylobacter or severe traveller's diarrhoea; metronidazole 400 mg three times daily for 5 days for Giardia.
Clostridioides difficile (C. diff)
C. difficile infection typically follows recent antibiotic use and presents with profuse, offensive, liquid stool, fever, and raised WCC. First-episode non-severe C. diff is treated with oral vancomycin 125 mg four times daily for 10 days (NICE NG199 — now first-line over metronidazole). Severe C. diff (WCC >15, temperature >38.5°C, rising creatinine) requires oral vancomycin 500 mg QDS. Fidaxomicin 200 mg twice daily for 10 days is preferred for recurrent episodes (NICE NG199). Patients should be isolated and contact precautions implemented. Stop causative antibiotics if possible.
Chronic Diarrhoea
Chronic diarrhoea persisting beyond four weeks requires systematic investigation: FBC, CRP, coeliac serology, stool calprotectin (raised in IBD, normal in IBS), stool MCS, and colonoscopy if indicated. Treatment depends on the underlying cause: gluten-free diet for coeliac disease; aminosalicylates or biologics for IBD; colestyramine for bile acid malabsorption. Pancreatic exocrine insufficiency causing steatorrhoea is managed with pancreatic enzyme replacement therapy (Creon). Review all medications for diarrhoea as a side effect — metformin, SSRIs, PPIs, magnesium-containing antacids.