Peptic Ulcer Disease Study Guide PDF

**1. Peptic Ulcer Disease (PUD) Overview:** - **Definition**: Peptic ulcers are open sores that develop in the esophagus, stomach, or small intestine. They form when the protective mucus lining is compromised, allowing stomach acid to \"eat away\" at the tissues. - **Common Locatio...

**1. Peptic Ulcer Disease (PUD) Overview:** - **Definition**: Peptic ulcers are open sores that develop in the esophagus, stomach, or small intestine. They form when the protective mucus lining is compromised, allowing stomach acid to \"eat away\" at the tissues. - **Common Locations**: Ulcers most often occur in the stomach's lesser curvature and the duodenum. - **H. pylori**: Most ulcers are caused by an infection with **Helicobacter pylori**. The bacteria weaken the mucus layer, which allows stomach acid to damage the tissues and form ulcers. **2. Goals of Drug Therapy:** - Alleviate symptoms like pain and discomfort. - Promote healing of existing ulcers by reducing acid production and strengthening protective mechanisms. - Prevent complications like bleeding or perforation. - Reduce ulcer recurrence by eradicating H. pylori and maintaining adequate protection. **3. Categories of Drugs for PUD:** - **Antibiotics**: Target and eradicate **H. pylori**, the main bacterial cause of ulcers. - **Antisecretory Agents**: - **Proton Pump Inhibitors (PPIs)**: Suppress gastric acid production, allowing the ulcer to heal by reducing acid exposure. - **Histamine-2 Receptor Blockers (H2 blockers)**: Reduce the secretion of stomach acid by blocking histamine receptors in the stomach. - **Mucosal Protectants**: Form a barrier over the ulcer, protecting it from acid so it can heal. - **Antisecretory Agents Enhancing Mucosal Defenses**: Help boost the body's natural protective mechanisms against stomach acid. - **Antacids**: Neutralize existing stomach acid to provide immediate symptomatic relief. **Development of Peptic Ulcers: Balance of Defensive vs. Aggressive Factors** **1. Imbalance of Factors:** - **Ulcers form** when there is an imbalance between **defensive factors** (which protect the stomach lining) and **aggressive factors** (which harm the stomach lining). **2. Defensive Factors:** These protect the stomach lining and prevent ulcers: - **Mucus**: Forms a protective barrier to shield the stomach and intestines from the acidic environment. - **Bicarbonate**: Neutralizes stomach acid to reduce damage to the lining. ### **3**. **Prostaglandins:** - **Stimulate mucus and bicarbonate production** to protect the stomach lining. - **Promote blood flow** to the stomach, ensuring tissue health and repair. - **Suppress gastric acid production**, reducing the risk of acid damage. **3. Aggressive Factors:** These contribute to the development of ulcers by damaging the protective lining: - **H. pylori**: A gram-negative bacterium that weakens the protective mucus layer, making the stomach lining more susceptible to damage by acid. - **NSAIDs (Nonsteroidal Anti-Inflammatory Drugs)**: Medications like ibuprofen and aspirin **inhibit the production of prostaglandins**. This: - **Decreases submucosal blood flow**, reducing the stomach\'s ability to maintain its protective barrier. - **Suppresses the secretion of mucus and bicarbonate**, weakening the defense against stomach acid. - **Promotes the secretion of gastric acid**, increasing the risk of damage to the stomach lining. - **Gastric Acid**: The strong acid in the stomach can erode the lining if there's not enough mucus to protect it. - **Pepsin**: Normally breaks down food proteins, but when the mucus barrier is weakened, it can attack the stomach's own tissue, contributing to ulcer formation. - **Smoking**: Delays ulcer healing and increases recurrence by: - Reducing the effectiveness of antiulcer medications. - Reducing bicarbonate secretion. - Accelerating gastric emptying, which increases acid delivery to the duodenum. ### ### **Drug Classification for Promoting Ulcer Healing**: Drugs for peptic ulcer disease (PUD) work in three primary ways: 1. **Eradicate H. pylori**: This is done with **antibiotics**. 2. **Reduce Gastric Acidity**: Achieved by: - **Antisecretory agents**: Proton Pump Inhibitors (PPIs) and Histamine-2 (H2) Receptor Antagonists. - **Antacids**: Neutralize stomach acid. - **Misoprostol**: Also helps reduce acid. 3. **Enhance Mucosal Defenses**: Done with: - **Mucosal protectants**: Such as **sucralfate**. - **Misoprostol**: Enhances mucosal defense while also reducing acid. **Treatment** ### **H. pylori-Associated Ulcers**: - **Treatment**: Antibiotics to eradicate H. pylori. - **Antisecretory agents** (PPIs or H2 blockers) are also given to reduce acid, promote healing, relieve symptoms, and enhance antibiotic effectiveness. ### **NSAID-Induced Ulcers**: - **Prophylaxis**: For high-risk patients, **PPIs** (e.g., omeprazole) are preferred for preventing ulcers. **Misoprostol** is also effective but can cause diarrhea. **Antacids, sucralfate, and H2 blockers** are not recommended for prevention. - **Treatment**: **H2 receptor blockers** and **PPIs** are preferred. If possible, stop the NSAID to speed up healing. If NSAID use must continue, a **PPI** is the best choice for healing. ### Prototype Drugs for Peptic Ulcer Disease (PUD): - **Antibiotics (for H. pylori)**: - **Amoxicillin, clarithromycin, omeprazole** (used together to eradicate H. pylori). - **Histamine-2 Receptor Antagonist (H2RA)**: - **Cimetidine** (suppresses gastric acid secretion to promote healing). - **Proton Pump Inhibitor (PPI)**: - **Omeprazole** (blocks acid production to aid healing). - **Mucosal Protectant**: - **Sucralfate** (forms a protective barrier over ulcers to promote healing). - **Antacids**: - **Aluminum hydroxide/magnesium hydroxide** (neutralizes stomach acid to provide symptomatic relief). ### **Nondrug Therapy for Ulcers**: - **Diet**: A traditional \"ulcer diet\" (bland foods and milk) does not speed healing. Eating 5-6 small meals a day may help stabilize stomach pH. - **Other Measures**: - **Smoking**: Increases ulcer risk and delays healing, so it should be avoided. - **NSAIDs**: Should be avoided due to their ulcer-causing effects, except for low-dose aspirin used for heart disease. ### Antibacterial Drugs for H. pylori-Associated Ulcers: **\"Acid Blocks Bad Tummy Microbes Completely\"** - **Clarithromycin**: - **MOA**: **C**uts off protein production (inhibits protein synthesis). - **Side effects**: \"**C**lare can\'t taste, she's nauseous and has diarrhea\" (**taste distortion, nausea, diarrhea**). - **Tetracycline**: - **MOA**: **same as above** - **Side effect**: \"**T**eeth staining\" (avoid in children and pregnant women). - **Amoxicillin**: - **MOA**: **A**ttacks the bacterial cell wall (disrupts cell wall). - **Side effect**: \"**A**mo causes diarrhea\" (**diarrhea**). - **Bismuth Compounds**: - **MOA**: **B**reaks the bacterial wall and blocks it from sticking (disrupts cell wall, prevents adhesion). - **Side effects**: \"**B**lack tongue or black stool\" (harmless discoloration). - **Metronidazole**: - **MOA**: **M**angles DNA (disrupts DNA). - **Side effects**: \"**M**etro gives headaches, nausea, and reacts with alcohol\" (**headache, nausea, disulfiram-like reaction with alcohol**). Not safe in preggo - **Tinidazole**: - **MOA**: Similar to metronidazole - **Side effects**: \"**T**inidazole + Alcohol = Trouble\" (**disulfiram-like reaction with alcohol, not safe in pregnancy**). ### Antibiotic Combinations (with Shortcuts): 1. **Clarithromycin-Based Triple Therapy (PAC)/PMC if allergic to A**: - **P**: **PPI** (e.g., omeprazole) - **A**: **Amoxicillin** - **C**: **Clarithromycin** 2. **Bismuth-Based Quadruple Therapy (BMPT)**: - **B**: **Bismuth** - **M**: **Metronidazole** - **P**: **PPI** - **T**: **Tetracycline** 3. **Sequential Therapy (5+5)**: - **First 5 days**: **PPI + Amoxicillin** - **Next 5 days**: **PPI + Clarithromycin + Tinidazole** ### H2 Receptor Antagonists (H2RAs) for Ulcer Treatment: - **MOA**: H2RAs promote ulcer healing by **suppressing gastric acid secretion**. - **Common Drugs**: **Cimetidine, ranitidine, famotidine, nizatidine**---all are equally effective. ### Cimetidine Key Points: - **Routes**: Can be administered **orally, intramuscularly (IM), or intravenously (IV)**. - **Absorption**: Food slows the rate of absorption but **prolongs effects**. - **Crosses the blood-brain barrier (BBB)**: Can cause **central nervous system (CNS) side effects**. - **Elimination**: Mostly excreted **intact in urine**. Dosage should be **reduced in patients with renal impairment**. ### Cimetidine Safety Points: - **CNS Effects**: Especially in **older adults** or those with **renal/hepatic impairment** (can cause confusion, hallucinations, and CNS depression/excitation). - **Antiandrogenic Effects**: Can cause **gynecomastia, reduced libido, and impotence**, which resolve after stopping the drug. - **Pneumonia Risk**: Increased risk of **pneumonia** due to reduced gastric acidity, but the overall risk is low (1 in 500). - **Drug Interactions**: Inhibits liver enzymes, increasing levels of drugs like **warfarin, phenytoin, theophylline, and lidocaine** (dose adjustments may be needed). - **Antacids**: **Decrease absorption** of cimetidine---administer at least 1 hour apart. ### Proton Pump Inhibitors (PPIs) Key Points: - **Most effective** drugs for **suppressing gastric acid** secretion. - **Indications**: Used for **gastric/duodenal ulcers**, **GERD**, and **Zollinger-Ellison syndrome**. - **Mechanism of Action**: Irreversibly inhibits the **proton pump (H+/K+-ATPase)** in stomach parietal cells, blocking acid production. - **Common Drugs**: **Omeprazole (prototype)**. - **Administration**: Short-term use (4-8 weeks) for ulcers and GERD; long-term use for hypersecretory conditions. - **Adverse Effects**: - **Pneumonia**: Increased risk during the first few days of therapy. - **Fractures**: Long-term use can reduce calcium absorption, increasing fracture risk. - **Rebound Acid Hypersecretion**: Sudden discontinuation can cause excessive acid production. - **Hypomagnesemia**: Long-term use may reduce magnesium levels. - **C. difficile Infection**: Increased risk of severe diarrhea due to **Clostridium difficile** infection. ### \"PPIs Have Real Danger\" - **P**: **Pneumonia** (increased risk, especially early in treatment) - **P**: **Poor bone health** (fractures and osteoporosis with long-term use) - **H**: **Hypomagnesemia** (low magnesium from long-term use) - **R**: **Rebound acid hypersecretion** (acid surge after stopping) - **D**: **Diarrhea** (due to **C. difficile** infection risk) - **Drug Interactions**: - **Reduces absorption** of some HIV drugs (atazanavir, nelfinavir) and antifungals (ketoconazole, itraconazole). - **Interaction with clopidogrel**: May reduce the beneficial antiplatelet effects, but often still used in high-risk patients to reduce GI bleeding. ### Sucralfate Key Points: - **Mechanism of Action (MOA)**: Sucralfate forms a **sticky gel** in acidic conditions (pH \< 4) that adheres to the ulcer crater, creating a **protective barrier** against acid, pepsin, and bile salts. - **Drug-Drug Interactions**: - **Antacids**: Can interfere with sucralfate's action by raising gastric pH. Administer at least **30 minutes apart**. - **Other drugs**: May reduce absorption of drugs like **phenytoin, digoxin, warfarin, theophylline, and fluoroquinolones**. Administer at least **2 hours apart**. ### Misoprostol Key Points: - **Mechanism of Action (MOA)**: Misoprostol is a **prostaglandin analog** that replaces the protective prostaglandins inhibited by NSAIDs. It helps **reduce gastric acid**, promotes **mucus and bicarbonate secretion**, and **increases blood flow** to the stomach lining. - **Major Safety Point**: - **Contraindicated in pregnancy** due to its ability to stimulate **uterine contractions**, which can cause miscarriage. Women of childbearing age must follow strict precautions (birth control, pregnancy testing, and warnings). ### Antacids Key Points: - **Mechanism of Action (MOA)**: Antacids are **alkaline compounds** that **neutralize stomach acid** by reacting with gastric acid to form neutral or low-acid salts. They also reduce **pepsin activity** when gastric pH is raised above 5. - **Major Safety Points**: - **Sodium loading**: Some antacids (e.g., sodium bicarbonate) contain high sodium, which can exacerbate **hypertension** and **heart failure**. - **Renal Calculi**: **Calcium carbonate** antacids can increase the risk of **kidney stones** (renal calculi), especially with long-term use. - **Hypermagnesemia**: **Magnesium-based antacids** can cause **hypermagnesemia**, particularly in patients with **renal impairment**. - **Drug interactions**: Antacids can interfere with the absorption of drugs like **cimetidine** and **sucralfate**. Administer antacids **1 hour apart** from these drugs. ### ### Constipation and Laxatives Key Points: - **Definition**: Constipation is based on **stool consistency** (hard/dry stools), not frequency of bowel movements. - **Common Causes**: **Low fiber/fluid diet**, **drug use** (e.g., opioids, anticholinergics), slow intestinal transit. - **Treatment**: - Increase **fiber, fluids, and exercise**. - Use **laxatives** only briefly and as an adjunct to lifestyle changes. - **Laxative Use**: - **Infants**: Docusate, lactulose, glycerin. - **Children**: Milk of magnesia, senna, docusate, bisacodyl. - **Pregnancy**: Use cautiously (may induce labor). - **Older Adults**: Monitor for **dehydration**. - **Indications**: Relieve painful defecation, avoid strain in patients with **cardiovascular disease**, prevent **fecal impaction**. - **Contraindications**: Abdominal pain, nausea, cramping, **bowel obstruction**, acute surgical abdomen, **fecal impaction**. ### Laxative Classification: - **Types of Laxatives**: 1. **Bulk-forming**: Adds fiber to bulk up stool. 2. **Surfactant**: Softens stool by allowing water to penetrate. 3. **Stimulant**: Stimulates bowel movement. 4. **Osmotic**: Draws water into the intestines to soften stool. - **Groups by Time and Consistency**: 1. **Group I**: Works fast (2--6 hours), produces watery stool. Used for prepping bowel for surgery or diagnostics. 2. **Group II**: Takes 6--12 hours, produces semifluid stool. Often abused. 3. **Group III**: Slow (1--3 days), produces soft but formed stool. Used for chronic constipation. ### Bulk-Forming Laxatives Key Points: - **Mechanism of Action**: Mimic **dietary fiber** by absorbing water, swelling, and forming a gel-like mass that softens stool and increases bulk. This stimulates **peristalsis**. - **Uses**: Preferred for **temporary constipation**, **diverticulosis**, and **irritable bowel syndrome (IBS)**. Can also relieve **diarrhea** and help patients with **ileostomy/colostomy**. - **Adverse Effects**: Minimal but can cause **esophageal or intestinal obstruction** if not taken with sufficient water. Always take with a **full glass of water or juice**. - **Examples**: **Psyllium**, **methylcellulose**, and **polycarbophil**. ### Surfactant Laxatives Key Points: - **Mechanism of Action**: Soften stool by **lowering surface tension**, allowing water to penetrate. May also **stimulate water and electrolyte secretion** into the intestines. - **Time to Effect**: Produce a soft stool in **1--3 days**. - **Administration**: Should be taken with a **full glass of water**. - **Example**: **Docusate sodium** (Colace). ### Stimulant Laxatives Key Points: - **Mechanism of Action**: Stimulate **intestinal motility** and increase **water and electrolyte secretion** into the intestines. - **Time to Effect**: Produce a semifluid stool in **6--12 hours**. - **Common Uses**: - **Opioid-induced constipation**. - **Constipation from slow intestinal transit**. - **Examples**: **Bisacodyl**, **senna**, **castor oil**. ### Key Side Effects/Considerations: - **Bisacodyl**: - Available as **tablets** (acts in 6-12 hours) and **rectal suppositories** (acts in 15-60 minutes). - **Tablets** are **enteric-coated** to prevent gastric irritation; avoid crushing or chewing. Take at least **1 hour after milk or antacids**. - **Suppositories** may cause a **burning sensation** and prolonged use can lead to **proctitis**. - **Senna**: - Derived from plants, acts in **6-12 hours**. - Can turn **urine yellow-brown or pink**, but this is **harmless**. - **Castor Oil**: - Acts quickly (within **2--6 hours**) and produces a **watery stool**. - Should be used only for rapid bowel evacuation, not for routine constipation due to its **powerful effects**. - Has an **unpleasant taste**; better when chilled and mixed with juice. ### Osmotic Laxatives Key Points: - **Mechanism of Action**: Draw water into the intestines, softening and swelling the stool to stimulate **peristalsis**. - **Time to Effect**: - Low doses: Work in **6--12 hours**. - High doses: Act rapidly within **2--6 hours** for bowel prep or toxin evacuation. - **Common Uses**: Bowel preparation for surgery or diagnostics, removing poisons or dead parasites. - **Examples**: - **Magnesium salts** (e.g., magnesium hydroxide) - **Sodium phosphate** - **Polyethylene glycol (PEG)**: Commonly used for chronic constipation. - **Lactulose**: Also used to lower **ammonia levels** in liver disease. - **Glycerin** - **Adverse Effects**: - **Dehydration**: Encourage patients to increase fluid intake. - **Magnesium toxicity**: Contraindicated in **renal impairment**. - **Sodium retention**: Can worsen **heart failure, hypertension**, and cause **acute renal failure** in vulnerable patients (e.g., those on ACE inhibitors, ARBs, diuretics). ### Patient-Centered Care Across the Life Span: - **Infants**: Safe options include **docusate, lactulose**, and **glycerin suppositories**. - **Children/Adolescents**: Use **milk of magnesia, mineral oil, senna, docusate**, and **bisacodyl**. - **Pregnant Women**: Use laxatives **cautiously**, as GI stimulation may induce **labor**. - **Breastfeeding Women**: **Senna** is safe, but caution is advised for **polyethylene glycol** and **bisacodyl**. - **Older Adults**: All laxatives are generally safe, but monitor closely for **dehydration**. ### Antiemetics Key Points: - **Emetic Response**: Triggered by the **vomiting center** in the brain, which can be activated by signals from the stomach, inner ear, or blood-borne substances. - **Key Receptors** involved in the emetic response: - **Serotonin (5-HT3) receptors**: Blocked by **ondansetron (Zofran)**. - **Glucocorticoid receptors**: Blocked by **dexamethasone**. - **Neurokinin-1 (NK1) receptors**: Blocked by **aprepitant (Emend)**. - **Dopamine receptors**: Blocked by **prochlorperazine**. - **Histamine (H1) receptors**: Blocked by **dimenhydrinate**. - **Acetylcholine (muscarinic) receptors**: Blocked by **scopolamine**. ### Serotonin Receptor Antagonists Key Points: - **Mechanism of Action**: Blocks **5-HT3 (serotonin) receptors** in the **CTZ** and on vagal neurons in the GI tract. - **Uses**: Effective for **chemotherapy-induced nausea and vomiting (CINV)**, nausea from **radiation**, **anesthesia**, **viral gastritis**, and **pregnancy**. - **Common Drugs**: **Ondansetron (Zofran)**, **granisetron**, **dolasetron**, **palonosetron**. ### Key Side Effects: - **Most common**: **Headache**, **diarrhea**, and **dizziness**. - **Serious**: Prolongs the **QT interval**, increasing the risk for **torsades de pointes** (life-threatening heart arrhythmia). Use cautiously in patients with **electrolyte imbalances**, **heart failure**, or those on other **QT-prolonging drugs**. - **PKU Concern**: Avoid ondansetron **ODT** in patients with **phenylketonuria (PKU)** due to the presence of **aspartame**. ### Aprepitant (Emend) Key Points: - **Mechanism of Action**: Blocks **neurokinin-1 (NK1) receptors** in the CTZ, preventing **substance P** from triggering nausea and vomiting. - **Uses**: Primarily for **preventing chemotherapy-induced nausea and vomiting (CINV)** and **postoperative nausea**. - **Duration**: Long-acting; useful for both **acute and delayed CINV**. - **Adverse Effects**: Common side effects include **fatigue, hiccups, dizziness**, and **diarrhea**. ### Dopamine Antagonists (Phenothiazines) Key Points: - **Mechanism of Action**: Block **dopamine-2 receptors** in the **CTZ** to suppress nausea and vomiting. - **Uses**: Effective for **surgery**, **chemotherapy**, and **toxins**. - **Common Drugs**: **Prochlorperazine**, **promethazine** (Phenergan). ### Key Side Effects: - **Extrapyramidal reactions (EPS)**, **anticholinergic effects**, **hypotension**, and **sedation**. - **Contraindications**: - Avoid in patients with **Parkinson's disease** (worsens motor symptoms due to dopamine blockade). - Caution with **lithium** use due to increased risk of **EPS**. - **Promethazine Black Box Warning**: - Risk of **respiratory depression** (contraindicated in children under 2). - Risk of **tissue injury** with IV use, including **necrosis** and **gangrene**. ### Scopolamine Key Points: - **Class**: **Muscarinic antagonist**. - **Mechanism of Action**: Suppresses nerve traffic between the **vestibular apparatus** and the **vomiting center**, preventing motion sickness. - **Uses**: **Prevention and treatment** of motion sickness (best when used **prophylactically**). - **Common Side Effects**: **Dry mouth**, **blurred vision**, and **drowsiness**. - **More Severe Side Effects** (less common): **Urinary retention**, **constipation**, and **disorientation**. - **Administration**: Available as **oral, subcutaneous**, and **transdermal patches** (transdermal has less intense anticholinergic effects). ### Antihistamines for Motion Sickness Key Points: - **Common Drugs**: **Dimenhydrinate (Dramamine)**, **meclizine (Antivert)**, **cyclizine (Cyclivert)**. - **Mechanism of Action**: Block **H1 (histamine) receptors** and **muscarinic cholinergic receptors** in the pathway between the **inner ear** and the **vomiting center**. - **Side Effects**: - **Sedation** (from H1 receptor blockade). - **Dry mouth**, **blurred vision**, **urinary retention**, and **constipation** (from muscarinic receptor blockade). - **Effectiveness**: Less effective than **scopolamine** for motion sickness. ### Loperamide (Imodium) -- Anti-Diarrheal Key Points: - **Class**: Structural analog of **meperidine**. - **Mechanism of Action**: **Suppresses bowel motility** and reduces **fluid secretion** into the intestines. - **Uses**: Treats **diarrhea** and reduces discharge from **ileostomies**. - **Safety**: Poorly absorbed, does not cross the **blood-brain barrier**, and has **no potential for abuse**. - **Rare Risks**: May cause **toxic megacolon** or **colon dilation**, especially in patients with **inflammatory bowel disease (IBD)**. **4. Notable Terms:** - **H. pylori**: A bacterium that causes ulcers by weakening the stomach\'s mucus barrier. - **NSAIDs**: Nonsteroidal anti-inflammatory drugs that can cause ulcers by inhibiting prostaglandin production. - **Prostaglandins**: Compounds that protect the stomach lining by promoting mucus and bicarbonate secretion and maintaining blood flow. - **Gastric Acid**: Acid produced in the stomach that can damage the stomach lining if not controlled. - **Pepsin**: A digestive enzyme that can contribute to ulcer formation if not properly regulated. - **Cimetidine**: A prototype **H2 receptor antagonist** that suppresses gastric acid secretion. - **Proton Pump Inhibitors (PPIs)**: Drugs that block acid production by inhibiting the proton pump in the stomach. - **Omeprazole**: The prototype **PPI** that irreversibly inhibits the H+/K+-ATPase enzyme. - **Sucralfate**: A drug that forms a protective barrier over ulcers to shield them from acid and pepsin. - **Misoprostol**: A prostaglandin analog used to prevent NSAID-induced ulcers, contraindicated in pregnancy. - **Antacids**: Alkaline compounds that neutralize stomach acid and raise gastric pH. - **Renal Calculi**: Kidney stones, a risk associated with long-term use of **calcium carbonate** antacids. - **Hypermagnesemia**: Elevated magnesium levels, a risk with **magnesium-based** antacids in patients with renal impairment. - **Sodium Loading**: Excess sodium intake from antacids, which can worsen hypertension and heart failure. - **Surfactant Laxatives**: Laxatives that soften stool by lowering surface tension, allowing water to penetrate the stool (e.g., **docusate sodium**). - **Stimulant Laxatives**: Laxatives that stimulate intestinal motility and increase water secretion into the intestines (e.g., **bisacodyl**, **senna**). - **Osmotic Laxatives**: Laxatives that draw water into the intestines by osmosis, softening stool and promoting bowel movement (e.g., **magnesium hydroxide**, **polyethylene glycol**). - **Magnesium Toxicity**: A condition that can occur with excessive use of **magnesium-based** laxatives, especially in those with **renal impairment**. - **Polyethylene Glycol (PEG)**: An **osmotic laxative** used for chronic constipation and bowel cleansing before procedures (e.g., **MiraLAX**). - **Lactulose**: A **synthetic disaccharide laxative** used for chronic constipation and to reduce **ammonia levels** in patients with liver disease. - **5-HT3 Receptor Antagonists**: A class of antiemetics that block serotonin receptors, commonly used for chemotherapy-induced nausea (e.g., **ondansetron**). - **Neurokinin-1 (NK1) Receptor Antagonists**: Drugs like **aprepitant** that block substance P receptors to prevent nausea and vomiting, especially for chemotherapy and post-surgery. - **Dopamine Antagonists**: Drugs that block dopamine receptors in the chemoreceptor trigger zone (CTZ) to prevent nausea and vomiting (e.g., **prochlorperazine**). - **Extrapyramidal Symptoms (EPS)**: Movement disorders (e.g., tremors, rigidity) caused by dopamine antagonists, especially in conditions like Parkinson's disease or with **lithium** use. - **Scopolamine**: A **muscarinic antagonist** used for motion sickness by blocking nerve traffic from the vestibular apparatus to the vomiting center. - **Antihistamines for Motion Sickness**: Block H1 and muscarinic receptors to prevent nausea (e.g., **dimenhydrinate**, **meclizine**), with sedation as a prominent side effect. - **Loperamide (Imodium)**: An **anti-diarrheal** drug that reduces bowel motility and secretion, with potential risks for **toxic megacolon** in certain patients. - **Toxic Megacolon**: A severe dilation and inflammation of the colon, often associated with inflammatory bowel diseases, and can be life-threatening.