Step 1 Gastrointestinal
Gastrointestinal covers a wide swath of USMLE Step 1 — embryology, physiology, pathology, and pharmacology all show up, and the exam tests them together. Expect clinical vignettes where you need to know why a neonate has bilious vomiting, what electrolyte pattern accompanies pyloric stenosis, or which serologic marker distinguishes acute HBV from vaccination. Pure recall questions exist but are outnumbered by cases that require you to apply a mechanism to a clinical scenario. For anyone building a study plan around high-yield GI topics for Step 1, the look-alike pairs below are where most points are decided.
The trickiest parts are the areas where concepts look alike: Crohn vs UC, SCC vs adenocarcinoma of the esophagus, PBC vs PSC, choledocholithiasis vs cholangitis. Students routinely confuse PBC and PSC — PBC targets intrahepatic small ducts in middle-aged women with anti-mitochondrial antibodies, while PSC targets large ducts in young men with IBD. The exam loves to test whether you know the distinguishing detail — which direction SAAG cuts, which bilirubin fraction causes kernicterus, why a nontender palpable gallbladder means cancer and not stones.
USMLE GI pharmacology integrates constantly — PPIs appear in acid secretion questions, antiemetics show up in gastroparesis vignettes, and H. pylori eradication connects to MALT lymphoma and PUD. Another common misconception: students think GERD comes from acid overproduction, when it actually comes from LES incompetence. Know the GI hormones cold: source, stimulus, and target. Gastrin, CCK, secretin, and VIP each have tumor counterparts that the exam tests at least once. Build the physiology first and the Step 1 GI pharmacology becomes much easier to anchor.
Gut Tube Regions and Blood Supply
Arterial supply maps to foregut/midgut/hindgut boundaries, with the splenic flexure watershed tested most often.
- Misidentifies the splenic flexure watershed as SMA territory only
- Places the midgut-hindgut boundary at the hepatic flexure instead of the mid-transverse colon
Midgut Rotation and Anomalies (Malrotation/Volvulus)
Normal 270° counterclockwise rotation — when it fails, bilious vomiting in a neonate demands urgent surgery.
- Underestimates normal midgut rotation as 90° instead of 270°
- Attributes duodenal obstruction in malrotation solely to volvulus, overlooking Ladd bands
Meckel Diverticulum
True diverticulum from the vitelline duct, located in the distal ileum, diagnosed by Meckel scan for ectopic gastric mucosa.
- Misclassifies Meckel diverticulum as a false diverticulum
- Misplaces Meckel diverticulum in the jejunum rather than the distal ileum near the ileocecal valve
Omphalocele vs Gastroschisis
Peritoneal sac distinguishes omphalocele from gastroschisis, and chromosomal associations follow accordingly.
- Assigns the peritoneal sac to gastroschisis instead of omphalocele
- Attributes chromosomal syndrome associations to gastroschisis rather than omphalocele
Esophageal Atresia and Tracheoesophageal Fistula
The most common TEF variant has a distal fistula, causing polyhydramnios and requiring VACTERL workup at birth.
- Misplaces the fistula to the proximal pouch instead of the distal esophageal segment in the most common TEF variant
- Attributes polyhydramnios in EA/TEF to increased fetal urine rather than impaired fetal swallowing
Congenital Hypertrophic Pyloric Stenosis
Projectile non-bilious vomiting with hypochloremic metabolic alkalosis — fix electrolytes before the OR.
- Predicts metabolic acidosis in pyloric stenosis instead of hypochloremic metabolic alkalosis
- Prioritizes immediate surgery over pre-operative fluid and electrolyte resuscitation in pyloric stenosis
Hirschsprung Disease
Absent ganglion cells in the narrowed distal segment, confirmed by rectal suction biopsy showing absent Meissner and Auerbach plexuses.
- Identifies the dilated bowel as the aganglionic segment rather than the narrowed distal segment
- Limits the ganglionic absence in Hirschsprung disease to the submucosal plexus only
Portal-Caval Anastomoses
Three portosystemic connections explain esophageal varices, caput medusae, and rectal varices in portal hypertension.
- Attributes esophageal varices to the azygos vein rather than the left gastric-to-azygos anastomosis
- Misunderstands the direction of flow causing caput medusae in portal hypertension
Retroperitoneal Organs (SAD PUCKER)
SAD PUCKER organs lie retroperitoneal — Grey Turner and Cullen signs localize bleeding there, not intraperitoneally.
- Classifies the entire duodenum as retroperitoneal, ignoring that the first part is intraperitoneal
- Attributes Grey Turner and Cullen signs to intraperitoneal rather than retroperitoneal hemorrhage
Gastric Secretion and Cell Types
Parietal cells secrete acid and intrinsic factor; chief cells secrete pepsinogen — drug targets and pernicious anemia depend on this distinction.
- Assigns pepsinogen secretion to parietal cells instead of chief cells
- Attributes pernicious anemia to chief cell destruction rather than parietal cell loss
Bile Acids and Enterohepatic Circulation
CYP7A1 is rate-limiting for bile acid synthesis; reabsorption happens in the terminal ileum, not the proximal gut.
- Confuses HMG-CoA reductase (cholesterol synthesis) with CYP7A1 (bile acid synthesis) as the rate-limiting step
- Mislocates bile acid reabsorption to the proximal small intestine rather than the terminal ileum
GI Hormones (Gastrin, CCK, Secretin, GIP, Motilin, VIP, Somatostatin)
Each GI hormone has a distinct source cell and stimulus — secretin drives bicarbonate, CCK drives enzymes, and gastrinoma breaks the normal rules.
- Misattributes secretin release to gastric cells rather than duodenal S cells
- Conflates CCK and secretin as having identical pancreatic targets, missing that secretin drives bicarbonate while CCK drives enzymes
Site-Specific Absorption (Iron, Folate, B12)
Iron and folate absorb proximally; B12 absorbs only at the terminal ileum — site-specific disease predicts specific deficiencies.
- Mislocates iron absorption to the ileum or diffusely throughout the small bowel rather than the duodenum/proximal jejunum
- Conflates the absorption sites of folate (proximal small intestine) and B12 (terminal ileum)
Oral Mucosal Pathology
Scrapability separates oral candidiasis from leukoplakia; HPV-related SCC targets the oropharynx, not the oral cavity.
- Fails to use scrapability as the key bedside distinction between candidiasis and leukoplakia
- Mislocates HPV-related SCC to the oral cavity rather than the oropharynx
Salivary Gland Disorders
Facial nerve palsy with a parotid mass signals malignancy; pleomorphic adenoma recurs but is benign.
- Misclassifies pleomorphic adenoma as malignant based on its recurrence tendency
- Fails to recognize Warthin tumor as parotid-specific and potentially bilateral
GERD (Gastroesophageal Reflux Disease)
LES incompetence — not acid overproduction — drives GERD, and endoscopy is reserved for alarm features or Barrett screening.
- Attributes GERD to acid overproduction rather than LES incompetence
- Recommends routine endoscopy for all GERD rather than reserving it for alarm features or Barrett screening
Barrett Esophagus
Intestinal metaplasia with goblet cells defines Barrett; dysplasia grade determines surveillance interval and intervention.
- Defines Barrett metaplasia as gastric columnar epithelium rather than specifically intestinal metaplasia with goblet cells
- Applies uniform surgical management to Barrett esophagus without stratifying by dysplasia grade
Esophageal Cancer (SCC vs Adenocarcinoma)
SCC occupies the upper/mid esophagus with tobacco-alcohol risk; adenocarcinoma develops distally from Barrett with obesity as a driver.
- Swaps the risk factor profiles of esophageal SCC and adenocarcinoma
- Fails to recognize the progressive solid-then-liquid dysphagia pattern as the hallmark presentation of esophageal cancer
Achalasia
Loss of inhibitory myenteric neurons causes both failed LES relaxation and absent peristalsis — manometry confirms both are required.
- Attributes achalasia to LES muscle hypertrophy rather than loss of inhibitory myenteric neurons
- Misses that achalasia requires both failed LES relaxation and absent peristalsis on manometry, not just one finding
Mallory-Weiss vs Boerhaave
Mallory-Weiss tears the mucosa; Boerhaave ruptures full-thickness and demands surgery, not conservative management.
- Fails to distinguish Mallory-Weiss (mucosal tear) from Boerhaave (full-thickness rupture) by depth of injury
- Applies conservative management to Boerhaave syndrome, missing the need for urgent surgical intervention
Esophageal Varices
Portal hypertension shunts blood through the left gastric vein — non-selective beta-blockers serve both primary and secondary prophylaxis.
- Confuses direct wall injury with portosystemic shunting as the mechanism of varix formation
- Restricts non-selective beta-blocker use to secondary prophylaxis, missing their primary prophylaxis role
Zenker Diverticulum
Pulsion false diverticulum at the pharyngoesophageal junction causes regurgitation of undigested food in older adults.
- Misclassifies Zenker diverticulum as a true diverticulum rather than a false pulsion diverticulum
- Misplaces Zenker diverticulum in the mid or lower esophagus rather than at the pharyngoesophageal junction
Gastritis (Acute and Chronic A/B)
Type A autoimmune gastritis targets the fundus and carries carcinoid and adenocarcinoma risk; Curling ulcers follow burns, Cushing ulcers follow CNS injury.
- Inverts the gastric locations of Type A vs Type B chronic gastritis
- Inverts the triggers for Curling (burns) vs Cushing (CNS injury) stress ulcers
Peptic Ulcer Disease (Duodenal vs Gastric)
Duodenal ulcers hurt 2–3 hours after eating; gastric ulcers hurt with eating and require biopsy to exclude malignancy.
- Inverts the meal-pain relationship for duodenal vs gastric ulcers
- Attributes H. pylori mucosal injury to direct invasion rather than toxin-mediated and inflammatory mechanisms
Zollinger-Ellison Syndrome
Secretin paradoxically raises gastrin in gastrinoma; diarrhea reflects acid inactivating enzymes, not obstruction.
- Attributes ZES diarrhea to tumor obstruction rather than acid-mediated enzyme inactivation and mucosal injury
- Expects secretin to suppress gastrin in ZES, missing the paradoxical rise that defines the secretin stimulation test
Gastric Adenocarcinoma (Intestinal vs Diffuse)
Diffuse-type gastric cancer carries signet ring cells and CDH1 mutation; intestinal-type links to H. pylori and dietary nitrosamines.
- Assigns signet ring cell histology to intestinal-type rather than diffuse-type gastric adenocarcinoma
- Inverts the eponyms for supraclavicular nodal (Virchow) vs ovarian (Krukenberg) metastases of gastric cancer
MALT Lymphoma
H. pylori eradication alone can cure low-grade MALT lymphoma unless t(11;18) is present, predicting treatment failure.
- Overlooks H. pylori eradication as potentially curative monotherapy for low-grade gastric MALT lymphoma
- Attributes MALT lymphoma development to direct H. pylori oncogenic transformation rather than chronic antigen-driven B-cell stimulation
Celiac Disease
Anti-tTG IgA is the preferred serologic test; biopsy targets the duodenum and shows villous atrophy with crypt hyperplasia.
- Selects anti-gliadin antibodies as the preferred serologic test rather than anti-tTG IgA
- Misidentifies the ileum rather than the duodenum/proximal jejunum as the biopsy site for celiac disease
Whipple Disease
Tropheryma whipplei fills macrophages with PAS-positive material — cardiac and neurologic involvement requires prolonged antibiotics to prevent CNS relapse.
- Misidentifies the causative organism of Whipple disease as fungal or mycobacterial rather than Tropheryma whipplei
- Limits Whipple disease to GI malabsorption, missing its characteristic neurologic, cardiac, and articular manifestations
Small Bowel Obstruction
Adhesions dominate SBO after prior surgery; early obstruction produces high-pitched bowel sounds, not silence.
- Selects hernias over adhesions as the leading cause of SBO in adults with prior abdominal surgery
- Expects absent bowel sounds early in SBO rather than recognizing high-pitched hyperactive sounds as the early finding
Intussusception
Children under 2 rarely have a lead point and respond to pneumatic reduction; adults usually need surgery for an identifiable lead point.
- Confuses the typical age group and lead-point requirement between pediatric and adult intussusception
- Overestimates the frequency of the complete classic triad in intussusception
Volvulus (Sigmoid and Cecal)
Sigmoid volvulus decompresses endoscopically; cecal volvulus requires surgery — confusing them leads to the wrong initial management.
- Confuses sigmoid volvulus management with cecal volvulus by defaulting to immediate surgery
- Incorrectly applies endoscopic decompression to cecal volvulus instead of recognizing it requires surgery
Mesenteric Ischemia
Pain dramatically out of proportion to the abdominal exam is the classic clue to acute mesenteric ischemia.
- Misses the hallmark 'pain out of proportion to exam' in acute mesenteric ischemia
- Confuses embolism with thrombosis as the leading cause of acute mesenteric ischemia
Carcinoid Tumor and Syndrome
Liver metastases are required for GI carcinoids to cause the syndrome; 5-HIAA in urine, not serum serotonin, is the diagnostic marker.
- Misses that liver metastases are required for GI carcinoid tumors to produce carcinoid syndrome
- Fails to link tryptophan diversion by carcinoid tumors to niacin deficiency and pellagra
Irritable Bowel Syndrome
Rome IV criteria make IBS a positive diagnosis — alarm features like rectal bleeding or nocturnal symptoms mandate investigation.
- Treats IBS as a diagnosis of exclusion requiring full workup rather than a positive symptom-based diagnosis
- Overlooks rifaximin and alosetron as pharmacologic options for IBS-D beyond loperamide
IBD — Ulcerative Colitis vs Crohn Disease
Crohn causes transmural skip lesions anywhere in the GI tract; UC produces continuous mucosal inflammation confined to the colon.
- Confuses the depth of bowel wall inflammation between UC and Crohn disease
- Attributes skip lesions and rectal sparing to UC rather than Crohn disease
IBD Management Overview
5-ASA maintains UC remission but lacks efficacy in Crohn; TNF inhibitors require tuberculosis and hepatitis screening before starting.
- Incorrectly extends 5-ASA maintenance therapy from UC to Crohn disease
- Confuses the induction role of corticosteroids with long-term maintenance therapy in IBD
Appendicitis
Periumbilical pain migrating to the RLQ follows luminal obstruction — perforated appendicitis with abscess may go to interval appendectomy.
- Misses the periumbilical-to-RLQ pain migration pattern that characterizes appendicitis
- Inverts the pathogenesis by placing bacterial infection before luminal obstruction in appendicitis
Diverticulosis and Diverticulitis
Diverticulosis bleeds briskly without inflammation; diverticulitis causes LLQ pain and fever, and colonoscopy waits 6–8 weeks post-resolution.
- Misclassifies colonic diverticula as true diverticula rather than false pulsion diverticula
- Attributes significant lower GI bleeding to diverticulitis rather than diverticulosis
Angiodysplasia
Heyde syndrome links aortic stenosis to right-colon vascular ectasias — colonoscopy is the first diagnostic step.
- Prioritizes angiography over colonoscopy as the initial diagnostic approach to angiodysplasia
- Mislocates angiodysplasia to the small bowel rather than the cecum and right colon
Hemorrhoids and Anorectal Disorders
Internal hemorrhoids above the dentate line are painless; a lateral anal fissure should raise suspicion for Crohn or other underlying disease.
- Confuses which hemorrhoid type causes pain based on location relative to the dentate line
- Misses the significance of a laterally located anal fissure as a red flag for underlying disease
Paralytic Ileus
Gas distributes diffusely on imaging in ileus versus a transition point in SBO — hypokalemia and opioids are reversible triggers.
- Over-relies on absent bowel sounds to diagnose ileus rather than using imaging
- Confuses the radiographic distribution of gas in ileus versus mechanical small bowel obstruction
Neonatal Jaundice (Physiologic, Breast Milk, Breastfeeding, Pathologic)
Any jaundice in the first 24 hours is pathologic; breastfeeding jaundice peaks early from low intake, breast milk jaundice peaks late from inhibitory factors.
- Conflates breastfeeding jaundice (early, inadequate intake) with breast milk jaundice (late, inhibitory substances in milk)
- Misclassifies jaundice in the first 24 hours as potentially physiologic rather than always pathologic
Small Intestinal Bacterial Overgrowth (SIBO)
Bacterial overgrowth consumes B12 but synthesizes folate, flipping the expected deficiency pattern seen in other malabsorptive states.
- Misses that SIBO increases folate while decreasing B12, the opposite of the usual malabsorption pattern
- Oversimplifies the hydrogen breath test by not distinguishing lactulose from glucose substrates
Abdominal Wall Hernias (Inguinal, Femoral, Umbilical, Spigelian, Hiatal)
Indirect inguinal hernias pass through the internal ring; femoral hernias carry higher incarceration risk and skew female.
- Confuses the path of direct inguinal hernias with that of indirect hernias through the internal inguinal ring
- Incorrectly assigns male predominance to femoral hernias by analogy with inguinal hernias
Cleft Lip and Cleft Palate (Orofacial Clefts)
Cleft lip reflects failed fusion of the maxillary and medial nasal processes; cleft palate is a separate defect with its own syndromic associations.
- Treats cleft lip and cleft palate as a single embryologic defect rather than two distinct fusion failures
- Misses key syndromic associations of cleft palate, particularly Pierre Robin sequence
Phosphate Binders (Sevelamer, Calcium-Based, Lanthanum)
Taken with meals to trap dietary phosphate in the gut — sevelamer is preferred over calcium-based binders when hypercalcemia is present.
- Misses that phosphate binders must be taken with meals to be effective
- Defaults to calcium-based binders without recognizing that sevelamer is preferred when hypercalcemia or vascular calcification is present
Colorectal Cancer
CEA monitors recurrence after resection, not screening; right-sided CRC bleeds occultly, left-sided CRC obstructs.
- Incorrectly applies CEA as a screening tool rather than a post-resection surveillance marker
- Reverses the classic presentations of right-sided versus left-sided colorectal cancer
Polyposis Syndromes (FAP, Lynch, Peutz-Jeghers, Juvenile)
FAP causes thousands of adenomas with APC mutation; Lynch syndrome causes few adenomas but high cancer risk via mismatch repair loss.
- Dismisses cancer risk in Peutz-Jeghers syndrome because hamartomas are not adenomas
- Conflates Lynch syndrome with FAP by attributing a polyposis phenotype to Lynch
Viral Hepatitis Overview (A-E)
HAV and HEV are fecal-oral and never chronic; HCV has the highest chronicity rate among the bloodborne hepatitis viruses.
- Underestimates the chronicity rate of HCV relative to HBV in adult infection
- Misses the window period of HBV infection where only anti-HBc IgM is detectable
HBV Serology Patterns
Window period shows only anti-HBc IgM; anti-HBs alone indicates vaccination, while anti-HBs plus anti-HBc marks resolved infection.
- Confuses anti-HBs from vaccination with anti-HBs from resolved infection
- Misidentifies the window period as a pan-negative serologic state rather than isolated anti-HBc IgM positivity
Autoimmune Hepatitis
Type 1 AIH carries ANA and anti-SMA; type 2 carries anti-LKM1 — treatment is immunosuppression, not antivirals.
- Assigns anti-LKM1 to type 1 AIH instead of type 2 AIH
- Confuses AIH management with antiviral therapy rather than immunosuppression
Cirrhosis and Portal Hypertension
SAAG ≥1.1 points to portal hypertension; MELD drives transplant allocation, and stellate cell activation drives fibrosis.
- Inverts the SAAG threshold interpretation, attributing high SAAG to exudative rather than portal hypertensive ascites
- Confuses Child-Pugh with MELD as the transplant allocation tool
Cirrhosis Complications (SBP, HRS, HE)
SBP diagnosis requires PMN ≥250 on ascites tap; HRS demands vasoconstrictors plus albumin, not fluids alone.
- Requires culture positivity to diagnose SBP rather than using the PMN threshold
- Treats HRS with fluids alone rather than vasoconstrictors plus albumin
Wilson Disease
ATP7B mutation impairs copper excretion into bile — Kayser-Fleischer rings, liver disease, and neuropsychiatric symptoms together with low ceruloplasmin guide diagnosis.
- Treats Kayser-Fleischer rings as pathognomonic for Wilson disease rather than highly suggestive
- Over-relies on low ceruloplasmin as a standalone confirmatory test for Wilson disease
Hereditary Hemochromatosis
Transferrin saturation screens first; HFE mutation causes hepcidin deficiency, leading to unrestricted intestinal iron absorption.
- Uses ferritin rather than transferrin saturation as the primary screening test for hemochromatosis
- Attributes hemochromatosis to a direct transporter defect rather than hepcidin deficiency
Alpha-1 Antitrypsin Deficiency
Misfolded A1AT accumulates as PAS-positive globules in hepatocytes; emphysema is panacinar and lower-lobe, not upper-lobe.
- Applies the same loss-of-function mechanism to both liver and lung disease in A1AT deficiency
- Confuses A1AT liver biopsy findings with iron deposits rather than PAS-positive globules
Reye Syndrome
Aspirin during a viral illness triggers mitochondrial dysfunction causing microvesicular steatosis without hepatic inflammation.
- Expects inflammatory necrosis in Reye syndrome rather than non-inflammatory microvesicular steatosis
- Misses the specific aspirin-viral illness combination that triggers Reye syndrome
Hepatocellular Carcinoma
HBV can cause HCC without cirrhosis via direct oncogenic integration — AFP monitors but imaging criteria confirm diagnosis.
- Assumes HBV requires cirrhosis to cause HCC, missing its direct oncogenic mechanism
- Relies on AFP elevation alone to diagnose HCC rather than imaging criteria
Liver Abscess and Budd-Chiari
Amebic abscess responds to metronidazole alone; Budd-Chiari occludes hepatic veins and causes caudate lobe hypertrophy.
- Applies surgical drainage to amebic abscess, which responds to metronidazole without drainage
- Confuses Budd-Chiari with portal vein thrombosis rather than hepatic vein occlusion
PBC vs PSC (Cholestatic Liver Disease)
PBC targets intrahepatic small ducts in middle-aged women with anti-mitochondrial antibodies; PSC targets large ducts in young men with IBD.
- Swaps the demographic profiles of PBC and PSC
- Confuses which duct size/location is targeted in PBC vs PSC
Cholelithiasis (Gallstones)
Cholesterol stones form from bile supersaturation, not dietary intake; pigment stones split by infection (brown) versus hemolysis (black).
- Confuses the location and etiology of black vs brown pigment stones
- Attributes cholesterol stone formation to dietary cholesterol rather than bile supersaturation
Acute Cholecystitis
Cystic duct obstruction triggers the cascade from colic to infection — ultrasound confirms, and cholecystectomy timing depends on fitness.
- Confuses the time course of biliary colic with acute cholecystitis
- Over-relies on Murphy's sign as diagnostic rather than as a clinical clue requiring imaging confirmation
Choledocholithiasis and Ascending Cholangitis
Reynolds' pentad adds shock and confusion to Charcot's triad, signaling septic cholangitis requiring emergent ERCP.
- Fails to recognize Reynolds' pentad as a sign of septic shock requiring emergent intervention beyond Charcot's triad
- Conflates choledocholithiasis (obstruction alone) with ascending cholangitis (obstruction plus infection)
Biliary Atresia
Conjugated hyperbilirubinemia in a neonate is never physiologic — Kasai portoenterostomy must be done before 8 weeks for best outcome.
- Dismisses prolonged neonatal jaundice as physiologic rather than recognizing conjugated hyperbilirubinemia as a red flag
- Underestimates the time-sensitivity of the Kasai procedure in biliary atresia
Acute Pancreatitis
Lipase outperforms amylase for diagnosis; early enteral nutrition beats prolonged NPO, and ERCP is reserved for gallstone pancreatitis with biliary obstruction.
- Prefers amylase over lipase as the diagnostic marker for acute pancreatitis
- Advocates prolonged NPO in acute pancreatitis rather than early enteral nutrition
Chronic Pancreatitis
Exocrine failure precedes endocrine failure — fat-soluble vitamin deficiencies and steatorrhea follow, with alcohol and CFTR mutations as leading causes.
- Reverses the sequence of exocrine vs endocrine failure in chronic pancreatitis
- Missing genetic/idiopathic etiologies of chronic pancreatitis in younger patients
Pancreatic Adenocarcinoma
A palpable non-tender gallbladder (Courvoisier sign) points to malignant obstruction, not stones — CA 19-9 monitors, not screens.
- Confuses the presentation of head vs body/tail pancreatic tumors with respect to jaundice
- Misuses CA 19-9 as a screening marker rather than a monitoring marker for pancreatic cancer
Proton Pump Inhibitors
Irreversible H+/K+-ATPase inhibitors must be taken before meals and cause B12, magnesium, and iron deficiency with long-term use.
- Confuses the PPI target (H+/K+-ATPase) with the H2 receptor
- Misses that PPI efficacy depends on dosing before meals to target active proton pumps
H2 Receptor Blockers
Cimetidine uniquely inhibits CYP450 and has antiandrogenic effects — gynecomastia and drug interactions do not apply to other H2 blockers.
- Generalizes cimetidine's CYP450 inhibition to all H2 blockers
- Overestimates H2 blocker efficacy by ignoring the remaining gastrin and acetylcholine stimulatory pathways
Antacids, Sucralfate, Misoprostol
Magnesium antacids cause diarrhea, aluminum causes constipation; sucralfate needs acid to activate, and misoprostol is contraindicated in pregnancy.
- Confuses cation-specific GI side effects of magnesium vs. aluminum antacids
- Confuses sucralfate as acid-independent when it actually requires acid for activation
Antiemetics (Ondansetron, Metoclopramide)
Metoclopramide blocks D2 receptors and accelerates gastric emptying but causes extrapyramidal effects; ondansetron blocks 5-HT3 and prolongs QT.
- Confuses metoclopramide's D2 antagonism with ondansetron's 5-HT3 antagonism
- Confuses metoclopramide's extrapyramidal side effects with ondansetron's QT-prolongation risk
Laxatives and Antidiarrheals
Loperamide activates peripheral opioid receptors to reduce motility but is contraindicated when invasive pathogens are present.
- Confuses loperamide's opioid receptor mechanism with a non-specific water-absorption mechanism
- Confuses loperamide as universally safe for diarrhea when it is contraindicated in invasive infectious diarrhea
Hepatitis Antivirals (HBV and HCV)
HCV treatment with DAAs is curative in over 95% of cases; HBV antivirals suppress replication but do not eradicate the virus.
- Confuses HBV treatment (suppressive) with HCV treatment (curative)
- Confuses outdated interferon-based HCV therapy with current curative DAA regimens
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