I. Nonsteroidal Anti‑Inflammatory Drugs (NSAIDs)

Indications

Analgesic, anti‑inflammatory, and antipyretic therapy across many pediatric indications.

Mechanisms of injury

• Intestinal injury is largely acid‑independent and distinct from classic NSAID‑related gastric damage.
• COX‑1/COX‑2 inhibition decreases prostaglandin synthesis, producing localized mucosal ischemia and impaired mucosal integrity.
• Prostaglandins protect the gastric mucosa by stimulating mucus and bicarbonate secretion, maintaining mucosal blood flow, promoting epithelial cell restitution and repair, reducing acid secretion, and modulating local inflammation and motility
• Topical effects: phospholipid membrane lysis injures enterocyte mitochondria, causing cytosolic Ca2+ efflux, free radical formation, apoptosis, disruption of intercellular junctions, and increased mucosal permeability.
• Paracellular intrusion of bile acids, proteases, bacteria, and toxins elicits inflammation and ulcer formation mediated by neutrophil recruitment.
• NSAIDs exacerbate underlying inflammatory bowel disease; genetic susceptibility (e.g., CYP2C polymorphisms) may influence risk.

Adverse effects and clinical presentation

• Symptoms: abdominal pain, overt GI bleeding (upper or lower), occult bleeding/iron deficiency anemia, malabsorption, protein‑losing enteropathy, or asymptomatic mucosal injury.
• Endoscopic and anatomic patterns:
  • Duodenum: duodenitis, erosions, ulcers (bulb common).
  • Small bowel (ileum/jejunum): petechiae, villous blunting, small shallow round ulcers, punched/ring/longitudinal/irregular ulcers, circumferential ulcers with strictures, membranous stenosis, perforation, bleeding.
  • Diaphragm disease: circumferential membranous diaphragms resembling washers leading to obstructive symptoms and submucosal fibrosis columns on histology; surgical resection can be effective but recurrence/persistence occurs in ~50%.
  • Colon (often right sided): erythema, ulceration, nonspecific histology; nonerosive changes include neutrophilic inflammation and increased crypt apoptosis linked to prostaglandin inhibition.

Histopathology

• Duodenum: villous blunting, plasma‑cell–rich inflammation, neutrophils, and intraepithelial lymphocytosis.
• Enterocolitis patterns: crypt architectural distortion, pseudopyloric metaplasia, villous blunting with patchy chronic and active inflammation.
• Ulcers often nonspecific and not always associated with abundant chronic inflammation.

Treatment and prevention

• Discontinue NSAIDs when feasible; avoid routine coadministration of NSAIDs with PPIs due to potential alteration of the small‑bowel microbiome augmenting NSAID toxicity.
• Gastroprotective acid suppression has limited benefit for small bowel injury; mucoprotective agents (rebamipide where available) and probiotics (Lactobacillus rhamnosus GG) may reduce injury in some studies.
• Risk is dose‑independent across NSAIDs; enterohepatic‑circulating NSAIDs increase small bowel exposure and risk; COX‑2 selectivity does not reliably prevent intestinal injury.
• Surgical resection for diaphragm disease or refractory strictures; recurrence risk necessitates follow‑up.
• Use capsule endoscopy for diffuse small bowel assessment if no obstruction suspected; use cross‑sectional imaging and device‑assisted enteroscopy for biopsy and therapy planning.

Practical points

• Consider NSAID enteropathy in children with unexplained iron deficiency anemia, obscure GI bleeding, chronic abdominal symptoms, or history of NSAID exposure.
• Be cautious prescribing long‑term NSAIDs in children with IBD or other predisposing conditions.

II. Chemotherapeutics, Targeted Agents, and Immunotherapies

Indications

Used for malignancy and for nonmalignant autoimmune conditions (systemic lupus, Crohn disease, rheumatoid arthritis, ankylosing spondylitis, multiple sclerosis, scleroderma, psoriasis, amyloidosis) with potential GI toxicity.

Mechanisms of injury

• Disruption of mucosal barrier (“mucositis”) via direct cytotoxicity and release of proinflammatory cytokines from mucosal immune cells.
• 5‑Fluorouracil (5‑FU) causes mitotic arrest of crypt cells → loss of absorptive villous epithelium and increased secretory crypt cell ratio → secretory diarrhea when small bowel secretion exceeds colonic absorptive capacity.
• Irinotecan produces mucosal apoptosis, epithelial vacuolization, goblet cell hyperplasia, and mucin hypersecretion; early cholinergic diarrhea (hours) and late secretory/motility‑related diarrhea from active metabolite accumulation and mucosal injury.
• Targeted agents (EGFR, VEGF, mTOR inhibitors) disrupt repair, vascular integrity, and mucosal homeostasis leading to diarrhea, stomatitis, delayed healing, bleeding, or perforation.
• Immune checkpoint inhibitors (ICIs) induce immune‑mediated colitis through T‑cell–driven mucosal inflammation resembling IBD.

Adverse effects and clinical syndromes

• Symptoms: abdominal cramps, distension, diarrhea (potentially life‑threatening), stomatitis, fecal occult blood, constipation, intestinal perforation, fever, and peritonitic signs.
• Neutropenic enterocolitis (typhlitis): hemorrhagic necrotizing inflammation of terminal ileum/cecum during profound neutropenia (<100/mm3); common after leukemia induction or high‑dose chemo; associated with cytarabine, cisplatin, vincristine, doxorubicin, 5‑FU, mercaptopurine, thioguanine; bacterial/fungal overgrowth and sepsis risk.
• C. difficile infection is common due to antibiotic exposure during cancer care and mucosal compromise after chemotherapy.
• Ischemic colitis reported with some regimens (e.g., docetaxel) and with antiangiogenic therapies.
• Constipation is multifactorial (opioids, antiemetics, poor intake) and occurs in ~25–33% of patients; vincristine causes neuropathic delayed transit, peaking 3–10 days after dosing.

Treatment and prevention

• Modify infusion strategies and dose when supported by evidence to reduce toxicity.
• Diarrhea: loperamide and diphenoxylate/atropine first line; octreotide for refractory secretory diarrhea; other agents include absorbents, tincture of opium derivatives, acetorphan, and oral budesonide in selected contexts.
• Irinotecan: early cholinergic diarrhea treated with atropine; late diarrhea managed aggressively with high‑dose loperamide and supportive care.
• Neutropenic enterocolitis: broad‑spectrum antibiotics, bowel rest, supportive care, granulocyte support, and surgical consultation for clinical deterioration or perforation.
• C. difficile: treat per pediatric guidelines with oral vancomycin or fidaxomicin; consider fecal microbiota transplantation for recurrent/refractory pediatric cases with infectious disease input.
• Preventive supportive care: antiemetics, mucositis prevention (oral cryotherapy, palifermin in specific protocols), hydration, nutrition, and early involvement of gastroenterology and nutrition teams.
• ICI colitis: grade‑based corticosteroids and steroid‑sparing biologics (infliximab, vedolizumab) for refractory cases, coordinated with oncology.

III. Antibiotics (Detailed)

Indications

Antimicrobial therapy for bacterial infections and prophylaxis; high‑use classes in pediatrics include penicillins, cephalosporins, macrolides, clindamycin, and TMP‑SMX.

Mechanisms of injury

• Antibiotics disrupt normal gut flora, enabling overgrowth of pathogens (e.g., C. difficile) and altering metabolic function of the microbiome.
• Some antibiotics alter gut motility (e.g., amoxicillin/clavulanate, macrolides) producing diarrhea or prokinetic effects.
• Frequent culprits for C. difficile: many penicillins, clindamycin, cephalosporins, and TMP‑SMX.
• Hemorrhagic colitis associated with Klebsiella oxytoca has been linked to amoxicillin, ampicillin, and erythromycin.
• Proton pump inhibitors likely potentiate antibiotic‑associated diarrhea and C. difficile risk by altering gastric acidity and microbiome composition.

Adverse effects and presentation

• Diarrhea is common and nonspecific; severe presentations with abdominal pain, fever, and leukocytosis suggest C. difficile infection.
• Bloody diarrhea and severe cramps may indicate hemorrhagic colitis; consider testing and stool culture or molecular assays.

Management

• Stop the offending antibiotic when safe; supportive care and pathogen‑directed therapy (oral vancomycin or fidaxomicin for C. difficile) per pediatric infectious disease guidance.
• Consider probiotics selectively in high‑risk settings; evidence varies by strain and indication.

IV. Corticosteroids

Indications

Used for inflammatory, allergic, immunologic, and malignant disorders.

Adverse effects and GI risks

• Corticosteroids increase peptic ulcer risk, especially when combined with NSAIDs (risk approximately doubles).
• Reported GI complications: ulcers and bleeding, rare intestinal malakoplakia (yellowish papule/plaque/ulceration endoscopically), occasional sigmoid diverticular perforation, and visceral perforation in severe cases.

Prevention

• Limit steroid exposure to the lowest effective dose and duration; employ ulcer prophylaxis when combined with NSAIDs or in high‑risk patients.

V. Laxatives (Anthranoids e.g., Senna)

Indication

Used to treat constipation.

Mechanism of injury

• Anthranoid laxatives increase colonic motility by inducing epithelial cell apoptosis and altering colonic absorption/secretion; mucosal disruption triggers histamine, serotonin, and prostaglandin release increasing transit and luminal fluid.
• Melanosis coli is a nonspecific marker of increased apoptosis and can develop within months of anthranoid use.

Adverse effects and diagnosis

• Clinical: diarrhea and abdominal cramping.
• Endoscopy: dark brown (lipofuscin‑like) pigmentation of the colon (melanosis coli), often including appendix, rarely small intestine.
• Histology: lipofuscin‑like pigment within macrophages; PAS positive and iron stain negative helps distinguish from hemosiderin.

Treatment

• Discontinue or change the laxative; provide supportive care and manage dehydration/electrolyte disturbances when present.

VI. Antidiarrheals

Indications and classes

• Used for IBS and chronic noninfectious diarrhea.
• Classes: antimotility agents (e.g., loperamide), antisecretory agents (e.g., bismuth subsalicylate), and adsorbents (e.g., aluminomagnesium silicates).

Risks

• Excessive antimotility use can lead to fecal stasis, bacterial overgrowth, or toxic megacolon in severe infectious colitis; caution in C. difficile or bloody diarrhea.

VII. Immunosuppressants (General)

Indications

Treatment of inflammatory, autoimmune, and transplant‑related conditions.

Mechanisms and risks

• Increase susceptibility to opportunistic infections (e.g., CMV, fungal pathogens) and impair mucosal immune responses, complicating diagnosis and management of GI symptoms.

VIII. Diuretics

Indications

Heart failure, fluid overload, nephrotic syndrome, ascites, pleural effusion.

Mechanism of injury

• Volume depletion and reduced mesenteric perfusion may precipitate nonocclusive ischemic injury, most often involving the colon (watershed areas) and sometimes the small bowel.

Adverse effects and findings

• Clinical: crampy abdominal pain, hematochezia.
• Endoscopy: geographic ulceration and possible pseudomembrane formation with marked submucosal edema that can mimic a mass; healed ischemic lesions may form isolated strictures resembling Crohn disease.
• Histology: superficial mucosal necrosis with sparing of crypt bases (withered crypts), hemorrhage, and lamina propria hyalinization.

Treatment and prevention

• Treat underlying cardiac/vascular disease and optimize volume status; minimize excessive diuresis in at‑risk children.

IX. Proton Pump Inhibitors (PPIs)

Indication

Antacid therapy and acid suppression for reflux, ulcer disease, and prophylaxis.

Associations and risks

• Lansoprazole and other PPIs have been associated with microscopic colitis (lymphocytic and collagenous colitis), with lansoprazole having a stronger association in some reports.
• PPIs are part of an expanding list of medications linked to microscopic colitis and may carry a similar risk for community‑acquired C. difficile infection as antibiotic exposure due to microbiome alteration.

Risks of Long Term PPI Use

1. Infections

• Clostridioides difficile (C. diff): PPIs may increase the risk of this serious intestinal infection by reducing stomach acid, which normally helps kill harmful bacteria.

• Other infections: Reduced acid may also allow other pathogens to survive, increasing risk of pneumonia and enteric infections.

2. Nutrient Deficiencies

• Vitamin B12 deficiency: Acid is needed to absorb B12 from food. Long-term suppression may lead to anemia and neurological symptoms.

• Magnesium deficiency: Can cause muscle cramps, arrhythmias, and seizures.

• Calcium and iron absorption: May be impaired, potentially contributing to bone loss and anemia.

3. Bone Health

• Osteoporosis and fractures: Reduced calcium absorption may increase the risk of hip, spine, and wrist fractures, especially in older adults.

4. Kidney Disease

• Acute interstitial nephritis: An immune reaction that can damage the kidneys.

• Chronic kidney disease (CKD): Some studies suggest a link between long-term PPI use and gradual kidney function decline.

5. Gastrointestinal Changes

• Microscopic colitis: PPIs have been associated with lymphocytic and collagenous colitis, which cause chronic diarrhea.

• Small intestinal bacterial overgrowth (SIBO): Reduced acid may allow bacteria to overgrow in the small intestine, causing bloating and discomfort.

6. Dementia and Cognitive Decline

• Some observational studies suggest a possible link between long-term PPI use and increased risk of dementia, though evidence is mixed and not conclusive.

7. Cancer Risk

• Gastric cancer: There is ongoing debate about whether prolonged PPI use increases the risk of stomach cancer, especially in people with chronic H. pylori infection.

• Hypergastrinemia: Long-term acid suppression can lead to elevated gastrin levels, which may promote abnormal cell growth in the stomach lining.

X. Other Drug‑Induced Conditions and Agents

Microscopic colitis

• Associated with several medications: NSAIDs, lansoprazole, ranitidine, ticlopidine, flutamide, and others.
• Presentation: chronic watery diarrhea with often normal endoscopic mucosa but diagnostic histologic features (lymphocytic or collagenous patterns).

Ischemic colitis

• Linked to cocaine, amphetamine, estrogen, vasoconstrictors, and other agents causing vasospasm or hypoperfusion.

Infectious promotion and virulence

• Some drugs promote enteric infections by altering flora (pseudomembranous colitis from antibiotics), increasing virulence (Yersinia with deferoxamine), injuring mucosa (necrotizing enterocolitis from hyperosmolar formulas), or promoting bacterial overgrowth via hypoperistalsis (excessive loperamide).

XI. Drug‑Induced Pancreatitis

Common culprits and presentation

• Medications linked to acute pancreatitis in children include valproic acid, azathioprine/6‑MP, didanosine, certain antibiotics (metronidazole), corticosteroids (rare), and others; mechanisms may be idiosyncratic or dose‑related.
• Presentation: abdominal pain, vomiting, elevated amylase/lipase; manage per pediatric pancreatitis guidelines and promptly review medication lists.

XII. Diagnostic Approach to Suspected Drug‑Induced Bowel Injury

History and medication review

• Obtain a thorough medication, supplement, OTC/herbal, and recent hospital exposure history with precise timing relative to symptom onset; include chemotherapy, antibiotics, NSAIDs, immunosuppressants, PPIs, opioids, iron, laxatives, and other relevant agents.

Laboratory and stool testing

• Basic labs: CBC, CMP, inflammatory markers, albumin, iron studies, nutritional markers.
• Stool: C. difficile testing per local algorithm (PCR + toxin or multistep), fecal calprotectin for inflammatory patterns, fecal fat for steatorrhea, ova/parasite and multiplex PCR panels for infectious causes.

Endoscopy, imaging, and histology

• Endoscopy with targeted biopsies is often required to define mucosal injury and exclude IBD, infection, ischemia, or GVHD; deep small bowel biopsies where feasible.
• Capsule endoscopy is useful for diffuse small bowel mucosal disease but is contraindicated if strictures or diaphragm disease are suspected.
• Cross‑sectional imaging (CT/MR enterography) detects strictures, transmural disease, perforation, and complications.
• Histologic patterns: crypt apoptosis (MMF/thiopurines), diaphragms/submucosal fibrosis (NSAIDs), immune‑mediated colitis with lamina propria lymphoplasmacytic infiltration and ulceration (ICIs), nonspecific mucosal injury—clinicopathologic correlation is essential.

XIII. Management Principles

• Identify and discontinue the offending agent when clinically safe; coordinate with prescribing teams (oncology, transplant, infectious disease, pain management, primary care).
• Supportive care: IV fluids, bowel rest as needed, electrolyte correction, nutritional support; targeted therapies (antibiotics for superinfection, PPI for upper GI ulcers when appropriate).
• Immune‑mediated injuries: corticosteroids as first‑line for severe ICI colitis; escalate to infliximab or vedolizumab for steroid‑refractory disease with oncology coordination.
• Endoscopic and surgical interventions for bleeding control, dilation of short accessible strictures, resection for recurrent diaphragm disease, or for perforation.
• Long‑term follow‑up for chronic sequelae: malabsorption, strictures, recurrent bleeding, and post‑injury IBS‑like symptoms; involve nutrition, rehabilitation, and psychosocial support.

XIV. Prevention, Stewardship, and Patient Education

• Minimize unnecessary exposures to high‑risk medications; use narrowest effective antibiotic spectrum and shortest NSAID course appropriate for clinical needs.
• Implement GI‑protective measures in high‑risk pediatric patients per oncology/transplant protocols; consider mucoprotective adjuncts or probiotics selectively with awareness of variable evidence.
• Educate families on safe medication administration (upright posture, adequate fluids with oral pills) and early symptom reporting for prompt evaluation.

XV. Special Pediatric Considerations

• Pharmacokinetics, developmental physiology, and vulnerability to toxicities differ from adults; dosing, monitoring, and supportive care must be pediatric‑specific.
• Growth, nutrition, and developmental impacts of chronic GI injury require early involvement of nutrition and developmental services.
• Multidisciplinary coordination (infectious disease, oncology, transplant, pain, endocrinology, nutrition, surgery) is essential for complex cases and medication decisions.

XVI. Knowledge Gaps and Research Priorities

• Need pediatric randomized trials on microbiome‑targeted prevention of antibiotic‑ and NSAID‑related injury.
• Randomized pediatric studies on probiotics, mucoprotective agents, and strategies to prevent chemotherapy‑ and immunotherapy‑related GI toxicity are lacking.
• Mechanistic research into genetic susceptibility (drug‑metabolizing polymorphisms) and microbiome–drug interactions will inform individualized prevention strategies.