Chapter 57- H-2 antagonists

Question 1

H-2 Antagonists-Generic Medications

(-dine)

Answer 1

Cimetidine (Tagamet HB)
Ranitidine (Zantac)
Famotidine (Pepcid)
Nizatidine (Axid)

Question 2

H-2 Antagonists-MOA

Answer 2

Selectively block H2 receptors located on the parietal cells of the stomach.

By blocking these receptors, 70% of the hydrochloric acid is prevented from being released by the parietal cells.

This action further decreases the production of pepsin within the chief cells of the stomach.

Footnote

H2 receptors sites are also found in the heart. High levels of H2 antagonists may produce cardiac arrhythmias.

Question 3

H-2 Antagonists-Indications

Answer 3

Short-term treatment of active duodenal or benign gastric ulcers (promotes healing and decreases discomfort by reducing overall acid level)

Treatment of pathological hyper-secretory conditions such as Zollinger-Ellison syndrome (blocks the overproduction of hydrochloric acid that is associated with such conditions)

Prophylaxis of stress-induced ulcers and acute upper GI bleeding (blocking the production of acid protects the stomach lining, which is at risk because of decreased mucus production associated with extreme stress)

Treatment of erosive GERD (decreasing the acid being regurgitated into the esophagus will promote healing and decrease pain)

Relief of symptoms of heartburn, acid indigestion, and sour stomach (OTC preparations)

Question 4

Which H-2 antagonists are available in both oral and parenteral forms?

Answer 4

Cimetidine (prototype)
Ranitidine
Famotidine

Question 5

Which H-2 antagonist is only available in oral form?

Answer 5

Nizatidine

Question 6

Cimetidine (Prototype)

Answer 6

Associated with anti-androgenic effects including gynecomastia and galactorrhea.

Peak time: 1-1.5 hr

Metabolized in the liver, excreted in the urine

Half-life of 2hr

Known to cross the placenta and enter breast milk

Question 7

Ranitidine

Answer 7

Longer acting and more potent than cimetidine, not associated with the anti-androgenic adverse effects or the marked slowing of metabolism in the liver as cimetidine is.

Peak time: 5-15 min IV, 1-3hr oral

Metabolized in the liver, excreted in the urine

Known to cross the placenta and enter breast milk

Question 8

Famotidine

Answer 8

Similar to ranitidine, but more potent than either cimetidine or ranitidine.

Famotidine is approved for use in children age 1-16

Peak time: 1-3hr, duration of 6-15hr.

Metabolized in the liver, excreted in the urine.

Known to cross the placenta and enter breast milk

Question 9

Nizatidine

Answer 9

Newest drug in the H2 antagonist class

It differs from the other 3 drugs in that it is eliminated by the kidneys with no first-pass metabolism in the liver.

It is the drug of choice for patients with liver dysfunction and for those who are taking other drugs whose metabolism is slowed by the hepatic activity of the other three H2 antagonists.

Known to cross the placenta and enter breast milk

Question 10

H-2 antagonists-Contraindications & cautions

Answer 10

Caution use in patients with hepatic or renal dysfunction. (Hepatic dysfunction is not as much of a problem with nizatidine)

Care should also be taken if prolonged or continual use of these drugs is necessary because they may mask serious underlying conditions.

Question 11

H-2 antagonists-Adverse effects

Answer 11

GI effects of diarrhea or constipation

CNS effects of dizziness, headache, somnolence, confusion, hallucinations, rash, cardiac arrest; cardiac arrhythmias and hypotension (more commonly seen with IV or IM admin or with prolonged use) impotence and gynecomastia (more commonly seen with long term use of cimetidine)

Question 12

H-2 antagonists-Drug to Drug interactions

Answer 12

Cimetidine, famotidine, and ranitidine can slow the metabolism of the following drugs, leading to increase serum levels and possible toxic reactions:
Warfarin, phenytoin, BETA blockers, alcohol, quinidine, lidocaine, theophylline, chloroquine, benzo’s, nifedipine, pentoxifylline, TCA’s, procainamide, and carbamazepine.

There is a risk of increased salicylate levels if nizatidine is taken with aspirin.

Question 13

H-2 antagonists-Pre/post medication Assessment

Answer 13

Monitor results of lab testing, including liver and renal functions tests, to predict changes in metabolism or excretion of the drug that might require dose adjustment.

Assess cardiopulmonary status (if IV route is indicated) to evaluate the cardiac effects of the drug.

Administer oral drug with or before meals and at bedtime to ensure therapeutic levels when the drug is most needed.