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TERMS TO LEARN

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Anticholelithic Drug that can dissolve gallstones.
Antiemetic Prevents or alleviates nausea and vomiting.
Blood Dyscrasias Disorders of the cellular elements of the blood.
Chemoreceptor Trigger Zone Part of the brain that induces vomiting; located in the area postrema at the base of the 4th ventricle outside the BBB; it is exposed to medications/toxins in blood and CSF.
Gastroparesis Paralysis of the stomach.
Gynecomastia Growth of breast tissue in males.
Zollinger-Ellison Syndrome Associated with gastrin secreting tumors causing hypergastrinemia and acid hypersecretion; 90% of these patients have PUD.

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I. H2 BLOCKERS

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H2-RECEPTOR ANTAGONISTS

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Drug Pharmacokinetics Mechanism of Action Clinical Uses Side Effects
Cimetidine (Tagamet)
  • A: PO, IV; oral availability 40–50%

  • t1/2: 1.5–2.3 hours

  • M: Hepatic (partial)

  • E: Metabolites and parent drug excreted in urine

  • Decreases gastric acid secretion via competitive inhibition of H2 receptors on gastric parietal cells

  • PUD (heals gastric and duodenal ulcers and prevents their recurrence)

  • Prophylaxis for duodenal ulcers

  • Prophylaxis for stress-induced ulcers

  • GERD

  • Gastric hypersecretory conditions (ie, Zollinger-Ellison syndrome)

  • Headache

  • Gynecomastia with LTU due to antiandrogenic action (blocks the production and release of testosterone; can be used by transsexuals for breast development)

  • Inhibits P450 enzymes (except Famotidine)

Famotidine (Pepcid)
  • A: PO, IV; oral availability 37–45%

  • t1/2: 2.5–4 hours

  • M: Hepatic (partial)

  • E: Most eliminated in urine

  • Headache

  • Dizziness

  • Diarrhea

  • Inhibits P450 enzymes (except Famotidine)

Nizatidine (Axid)
  • A: PO; oral availability 75–100%

  • t1/2: 1.1–1.6 hours

  • M: Hepatic (partial)

  • E: Urine

Ranitidine (Zantac)
  • A: PO, IV; oral availability 30–88%

  • t1/2: 1.6–2.4 hours

  • M: Hepatic

  • E: Urine and feces

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II. ANTACIDS AND PROTON PUMP INHIBITORS

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ANTACIDS: DRUG FACTS

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Drug Pharmacokinetics Mechanism of Action Clinical Uses Side Effects
Aluminum hydroxide (Alternagel)
  • A: PO; not significantly absorbed

  • E: In feces; absorbed portion excreted in urine

  • Weak bases that react with gastric acid to produce salt and water

  • Increase gastric pH

  • Pepsin inactivated when gastric pH is >4

  • Symptomatic relief of GERD, PUD, esophagitis, and gastric hyperacidity

  • Safe for use during pregnancy

  • Better at healing duodenal ulcers than gastric ulcers

  • Calcium carbonate useful for treatment of hypocalcemia

  • Magnesium hydroxide useful as a laxative

  • Constipation (especially in elderly patients)

  • Hypophosphatemia

Calcium carbonate (Caltrate, TUMS)
  • A: PO; 30% absorbed (vitamin D–dependent)

  • E: Absorbed portion excreted in urine

  • Hypercalcemia

  • Metabolic alkalosis (milk-alkali syndrome)

Magnesium hydroxide (Phillips' Milk of Magnesia)
  • A: PO; not significantly absorbed

  • E: Absorbed portion excreted in urine

  • Strong laxative effect

Sodium bicarbonate (Brioschi)
  • A: PO

  • E: Absorbed portion excreted in urine

  • Metabolic alkalosis

Note that these agents are frequently combined to produce other medications (ie, aluminum hydroxide and magnesium hydroxide = Maalox).

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