Histamine H2 Blockers

Histamine H2-receptor blockers, also called H2-receptor antagonists or H2RAs, are medications that help reduce the production of gastric acid. They can be used to treat gastric and duodenal ulcers; gastroesophageal reflux disease, or GERD; heartburn; and Zollinger-Ellison syndrome, which is a rare condition caused by gastrin-secreting tumors. In addition, histamine H2-receptor blockers can be used to prevent stress-induced ulcers in critically ill patients.

Histamine H2-receptor blockers include cimetidine, which can be administered orally, intravenously, and intramuscularly; famotidine, which is given orally or intravenously; and nizatidine, which is given orally.

Now, in the stomach, on gastric parietal cells, histamine stimulates H2 receptors to secrete gastric acid to promote digestion. Histamine H2-receptor blockers obstruct these H2 receptors so histamine can't bind to them. This results in decreased gastric acid secretion and reduces the acidity of the gastric acid.

Alright, let's focus on cimetidine. Some of the common side effects of cimetidine are due to its actions on H2 receptors located outside the gastrointestinal tract. So, in the brain, side effects can include headaches, dizziness, and confusion. In the skin, cimetidine may cause pruritus and rash. Cimetidine also binds to androgen receptors, which can lead to sexual side effects like decreased libido, impotence, and gynecomastia. Rarely, cimetidine can cause hematological side effects like agranulocytosis and thrombocytopenia.

In addition, reduced production of gastric acid can favor bacterial growth in the stomach. This is associated with an increased risk of micro-aspiration and lung colonization, leading to pneumonia. Lastly, it's important to note that prolonged use of histamine H2-receptor blockers for 2 years or more may lead to vitamin B12 malabsorption and subsequent deficiency.

As far as contraindications go, cimetidine should be used with caution during pregnancy and breastfeeding, as well as in elderly patients who are at risk for delirium. Caution should also be used in patients with hepatic disease; and dose adjustments are needed for patients with renal disease.

Regarding interactions, antacids impair the absorption of cimetidine, so administration of these medications should be separated by one hour. Cimetidine also inhibits drug-metabolizing enzymes in the liver, so if taken with certain medications like warfarin or phenytoin, the rate these medications are eliminated from the body could be reduced, which can cause them to build up in the body.

Now, before administering a histamine H2-receptor blocker, be sure to obtain a baseline assessment of your patient, including vital signs, lung sounds, and neurological status. Then, review any recent diagnostic information, including renal and hepatic function, CBC, and vitamin B12 level; and check their medication administration record for medications that could interact with cimetidine. During care, monitor your patient closely for side effects, and evaluate the effectiveness of H2-receptor blocker therapy.

Finally, when educating your patient about H2-receptor blocker therapy, focus your teaching on safe self-administration. Be sure they understand why their medication is prescribed and the recommended length of treatment. For instance, if your patient is diagnosed with GERD, teach them that their medication is most effective if taken before or with meals. On the other hand, if they're diagnosed with a duodenal or peptic ulcer, instruct them to take their medication at bedtime. Also encourage them to eat a diet rich in vitamin B12 to prevent deficiency. Then, review common side effects of their prescribed medication, and ensure they understand when they should notify their health care provider.

Alright, as a quick recap…. Histamine H2-receptor blockers are medications that help reduce the production of gastric acid, and include cimetidine, famotidine, and nizatidine. Some common side effects of cimetidine include headaches, dizziness, and confusion; pruritus and rash; as well as decreased libido, impotence, and gynecomastia. Nursing considerations for H2-receptor blocker therapy include establishing a baseline assessment, monitoring for side effects, evaluating the effectiveness of histamine H2-receptor blocker therapy, and providing teaching for safe self-administration.