HISTAMINE2 RECEPTOR ANTAGONISTS (H2RAs)

What are H2RAs?

H2RAs are drugs that block H2 receptors on parietal cells in the stomach, decreasing gastric acid secretion.

What stimulates H2 receptors in the stomach?

H2 receptors are normally activated by histamine, released by vagal stimulation.

What do H2RAs decrease in the stomach?

H2RAs decrease both basal and stimulated gastric acid production.

Do H1 blockers affect gastric acid production?

No, H1 blockers such as diphenhydramine do not affect acid production.

What is the prototype of H2RAs?

The prototype of H2RAs is Cimetidine (Tagamet HB).

How is Cimetidine metabolized and excreted?

Cimetidine undergoes partial liver metabolism and is excreted unchanged in urine.

What conditions require dosage adjustment for H2RAs?

Dosage must be adjusted in cases of kidney or liver impairment.

What is one of the main actions of H2RAs?

H2RAs block H2 receptors on parietal cells, leading to decreased secretion of hydrochloric acid.

How does the IV form of H2RAs help in clinical settings?

The IV form has a rapid action, useful in acute GI bleeding.

For what conditions are H2RAs used?

H2RAs are used for peptic ulcer disease (PUD), GERD, esophagitis, GI bleeding due to stress ulcers, and Zollinger-Ellison syndrome.

What is the healing time for peptic ulcer disease with H2RA treatment?

Healing time for PUD is typically 6–8 weeks.

What risks do older adults face when taking H2RAs?

Older adults are at increased risk for CNS effects such as confusion, agitation, delirium, and disorientation.

What effect does renal and liver impairment have on H2RA dosing?

Renal and liver impairment require a reduction in H2RA dosage to avoid toxicity.

What are common adverse effects of H2RAs?

Common adverse effects include diarrhea, headache, dizziness, drowsiness, muscle aches, and fatigue.

What are less common, but important, adverse effects of Cimetidine?

Less common effects include mental confusion, delirium, gynecomastia in men, galactorrhea in women, and decreased sperm count.

What should be avoided when taking Cimetidine?

Cimetidine should be avoided if on many other drugs due to major interactions.

What major interactions does Cimetidine have with CYP450 enzymes?

Cimetidine inhibits CYP450 enzymes, increasing serum levels of many drugs.

What happens when Cimetidine is taken with Warfarin?

Cimetidine increases Warfarin effects, raising bleeding risk.

What is the effect of Cimetidine on Phenytoin?

Cimetidine can increase the risk of Phenytoin toxicity.

What commonly used drugs does Cimetidine decrease the effects of?

Cimetidine decreases the effects of Iron, Digoxin, and Tetracyclines.

What is the recommendation for oral liquid administration of H2RAs?

Always use a marked cup or syringe for measuring oral liquid.

What are therapeutic effects to assess in H2RA treatment?

Assess for decreased epigastric pain and ulcer healing.

What adverse effects should be monitored in patients receiving H2RAs?

Monitor for CNS impacts, GI disturbances, neuro effects, and reproductive impacts.

What are key patient teaching points for H2RA therapy?

Take Cimetidine with meals or at bedtime, and avoid antacids within 1 hour of taking H2RAs.

What lifestyle changes can help reduce reflux?

Elevate the head of the bed, avoid smoking, limit fats, and avoid lying down after eating.

What should patients avoid regarding OTC H2RAs?

Do not use OTC versions longer than 2 weeks without provider advice.

What is a critical nursing consideration for H2RA administration?

Educate patients never to take the medication with less than 8 oz of water.

What do H2RAs do for gastrointestinal conditions?

They block H2 receptors, decreasing gastric acid and pepsin, aiding conditions like PUD and GERD.

What should be monitored for critically ill patients on H2RAs?

Monitor for longer half-life and slower clearance due to decreased perfusion and kidney function.

What is the importance of recognizing drug interactions for H2RAs?

Recognizing drug interactions is crucial to prevent adverse effects, especially with Cimetidine.