Antibiotic Associated Diarrhea

Pathophysiology

Antibiotics alter bacterial flora causing loose watery stools.
Direct antibiotic effect on intestinal mucosa alters gut microbiota composition.
Normal gut flora suppression permits pathogenic bacteria and fungi overgrowth.
Decreased metabolism of non-digested carbohydrates and primary bile acids occurs.
Reduced production of short-chain fatty acids exacerbates osmotic load.

Category	Pathogens
Most Common	Clostridioides difficile (C. difficile).
Other Organisms	Staphylococcus, Candida, Enterobacteriaceae, Klebsiella.

Disease spectrum ranges from mild diarrhea to fulminant pseudomembranous colitis.
Mild illness features watery diarrhea, low-grade fever, mild abdominal pain.
Severe progression exhibits abdominal cramps, fever, yellowish mucosal plaques (pseudomembrane).
Extreme cases associate with toxic megacolon, systemic toxicity, multisystem organ failure.

Investigation	Utility And Interpretation
Target Population	Testing discouraged in children <2 years due to high asymptomatic carriage.
Stool Assays	Multistep approach recommended combining glutamate dehydrogenase (GDH) immunoassay, toxin A/B enzyme immunoassay (EIA), and nucleic acid amplification tests (NAAT).
Endoscopy	Indicated for suspected pseudomembranous colitis. Reveals 2-5 mm raised yellowish plaques on colonic mucosa.

Immediate cessation of offending antibiotic often resolves symptoms,.
Institute specific antimicrobial therapy for severe or persistent C. difficile colitis.

Severity/Scenario	Drug Choice And Dosage
First-Line (Mild-Moderate)	Oral Metronidazole 30 mg/kg/day in 4 divided doses for 7-10 days.
Severe/Refractory Disease	Oral Vancomycin 40 mg/kg/day in 4 divided doses (maximum 2 g/day) for 10-14 days.
Alternative Therapy	Fidaxomicin approved for children >6 months; efficacy equivalent to vancomycin.
Recurrent Disease	Pulsed-tapered oral vancomycin regimen over 4-6 weeks. Fecal microbiota transplantation utilized for multiply recurrent cases.

Probiotic administration significantly reduces overall incidence.
Lactobacillus rhamnosus GG and Saccharomyces boulardii strongly recommended for prevention.
Saccharomyces boulardii conditionally recommended specifically for preventing C. difficile-associated diarrhea.