Gastrointestinal Pharmacology: Acid-Suppressing Agents, Laxatives, and Antidiarrheals

A comprehensive set of practice flashcards focusing on acid-suppressing agents (H2 blockers, PPIs, antacids, protectants) and bowel management drugs (laxatives, stool softeners, antidiarrheals), emphasizing mechanisms, timing, adverse effects, and critical nursing considerations.

What is the mechanism of action of $H_2$ receptor antagonists such as cimetidine and famotidine?

They competitively block histamine $H_2$ receptors on gastric parietal cells, thereby decreasing gastric acid secretion.

What specific adverse effects and major drug interactions are associated with cimetidine?

Cimetidine can cause gynecomastia, galactorrhea, CNS effects in elderly patients, and cardiac arrhythmias with high-dose IV administration. As a CYP inhibitor, it significantly interacts with warfarin, phenytoin, and theophylline.

Why is famotidine generally preferred over cimetidine for GERD and peptic ulcer disease?

Famotidine is the preferred $H_2$ blocker because it has significantly fewer drug-drug interactions than cimetidine.

How do $H_2$ blockers and Proton Pump Inhibitors (PPIs) compare in terms of potency, onset of relief, and optimal dosing timing?

$H_2$ blockers are less potent, provide faster relief, and are often administered at night. PPIs are more potent, have an onset of $1\text{--}2\text{ hours}$ with maximum relief taking $1\text{--}2\text{ weeks}$, and are best taken in the morning $30\text{--}60\text{ minutes}$ before the first meal.

What is the mechanism of action and duration of Proton Pump Inhibitors (PPIs) like omeprazole and pantoprazole?

They block the final common pathway of acid secretion, irreversibly suppressing basal and stimulated acid production for $24\text{--}48\text{ hours}$ until new proton pumps are synthesized.

What are the significant long-term adverse risks associated with chronic PPI therapy?

Long-term use can lead to osteoporosis, hypomagnesemia, hypocalcemia, increased risk of Clostridioides difficile infection, and vitamin $B_{12}$ deficiency.

What essential medication interactions and discontinuation instructions apply to Proton Pump Inhibitors?

PPIs reduce the antiplatelet effectiveness of clopidogrel and must be separated by $2\text{ hours}$ from drugs requiring an acidic gastric environment (e.g., iron, azole antifungals). They must be tapered slowly to prevent rebound acid hypersecretion.

Why is pantoprazole preferred over omeprazole in cardiac and polypharmacy patients?

Pantoprazole has fewer drug-drug interactions than omeprazole, which specifically diminishes clopidogrel efficacy.

What is the mechanism of action and dosing protocol for the GI protectant sucralfate?

Sucralfate creates a physical and chemical barrier that adheres to the ulcer crater for up to about $6\text{ hours}$, protecting tissue from acid, pepsin, and bile salts. It is administered PO QID on an empty stomach ($1\text{ hour}$ before meals or $2\text{ hours}$ after meals and at bedtime) and must be separated from all other medications by $2\text{ hours}$.

What is the primary indication, mechanism, and absolute contraindication for misoprostol?

Misoprostol is a $PGE_1$ analog that increases protective mucus and bicarbonate production while enhancing mucosal blood flow to prevent NSAID-induced ulcers. It is strictly contraindicated in pregnancy due to its abortifacient effects.

What specific nursing protocols must female patients of childbearing potential follow before and during misoprostol treatment?

Patients must have a confirmed negative pregnancy test before starting therapy, begin taking the medication on day $2\text{ or }3$ of their menstrual period, and consistently use barrier contraception throughout therapy.

What are the primary adverse effects and renal considerations associated with aluminum hydroxide (Amphojel)?

It causes constipation and phosphate depletion. In patients with renal impairment, aluminum accumulation can lead to encephalopathy and osteomalacia.

What key adverse effects and administration guidelines apply to calcium carbonate (Tums)?

Calcium carbonate can cause constipation, acid rebound, hypercalcemia, and kidney stones. Patients should take other medications first before consuming the antacid.

What complications can occur if magnesium hydroxide (Milk of Magnesia) is given to a patient with renal insufficiency?

Impaired excretion leads to hypermagnesemia, which can cause cardiac arrhythmias, muscle weakness, and respiratory depression.

What is the onset, indication, and key nursing consideration for bisacodyl (Dulcolax)?

Bisacodyl directly stimulates intestinal motility for bowel preparation and acute constipation. Its onset is $6\text{--}8\text{ hours}$ orally and $15\text{--}60\text{ minutes}$ rectally. It must be taken with $8\text{ oz}$ of water, used for short-term therapy only, separated from other medications by $30\text{ minutes}$, and preceded by assessment for an acute abdomen.

What adverse effect and patient misconception are associated with senna (Senokot)?

Long-term use can cause colon discoloration. Patients must be taught that its natural plant-derived origin does not make it safe for chronic use, as it carries the same dependence risk as other stimulant laxatives.

How does psyllium (Metamucil) function, and what critical instruction prevents complications?

Psyllium absorbs water to increase fecal bulk and stimulate peristalsis for chronic constipation. It MUST be taken with at least $8\text{ oz}$ of water to prevent severe gastrointestinal obstruction.

What is the mechanism of action, onset, and clinical profile of polyethylene glycol (MiraLAX)?

Polyethylene glycol draws water into the intestinal lumen via osmotic pressure. It has an onset of $1\text{--}3\text{ days}$, causes minimal electrolyte disturbance, and is suitable for long-term management of chronic constipation rather than acute relief.

How does lactulose treat hepatic encephalopathy, and how is its dosage clinical endpoint evaluated?

Lactulose produces an osmotic laxative effect and acidifies the colon to trap ammonia; its dosage is titrated to achieve $2\text{--}3$ soft stools per day while monitoring mental status and serum ammonia levels.

What are the clinical indications, severe risks, and contraindications for magnesium citrate?

Magnesium citrate is used for bowel preparation before procedures ($30\text{ min -- }6\text{ hours}$ onset). It induces massive fluid shifts leading to dehydration, electrolyte imbalances, and hypermagnesemia, and is contraindicated in renal impairment.

What is the mechanism and therapeutic scope of docusate sodium (Colace)?

Docusate is a surfactant that facilitates water and fat penetration into the stool to soften it. It prevents straining (post-op, post-MI, postpartum) but does NOT stimulate motility and cannot treat pre-existing constipation.

When is the antidiarrheal agent loperamide strictly contraindicated?

Loperamide must NEVER be administered to patients with infectious, bloody, or febrile diarrhea.

What are the high-yield side effects, composition warnings, and pediatric restrictions for bismuth subsalicylate?

Bismuth subsalicylate causes harmless black discoloration of the tongue and stool. Because it contains salicylate, it is contraindicated in children under $12\text{ years}$ of age due to the risk of Reye's syndrome.