Histamine H2 antagonists: Nursing pharmacology

Histamine H2-receptor antagonists, also called H2 blockers, are medications that help reduce the production of gastric acid.

Because of that, they can be used to treat peptic ulcers; gastroesophageal reflux disease, or GERD; and Zollinger-Ellison syndrome, which is a rare condition caused by gastrin-secreting tumors.

In addition, histamine H2-receptor antagonists can be used to prevent stress-induced ulcers. These medications include cimetidine, which can be administered orally, intravenously, and intramuscularly; famotidine, which is given orally or intravenously; and nizatidine, which is given orally.Now, gastric acid is secreted by the parietal cells, which have different membrane receptors that modulate their activity.

One of them is the H2 histamine receptor. Normally, the stomach is protected from the acidic environment by the mucus secreted by foveolar cells, and the esophagus is protected by the lower esophageal sphincter, which prevents gastric acid from coming back up.

When some of these mechanisms fail, the person can develop peptic ulcers or gastroesophageal reflux disease. Histamine H2-receptor antagonists block H2 receptors so histamine can’t bind them, which decreases gastric acid secretion, and in turn mitigates the harmful effects of gastric acid in these disorders.Generally, histamine H2-receptor antagonists are safe medications.

However, they may cause some side effects, since H2 receptors are not only located in the stomach. So, in the brain, some side effects include headaches, dizziness, somnolence, confusion, and hallucinations.

In the skin, these medications may cause pruritus and a rash; while cardiovascular side effects include hypotension and cardiac dysrhythmias.

Histamine H2-receptor antagonists may lead to sexual side effects like decreased libido and impotence; as well as gastrointestinal side effects like diarrhea or constipation.

In addition, histamine H2-receptor antagonists reduce the production of gastric acid, which can favor bacterial growth in the stomach; this is also associated with an increased risk of microaspiration and lung colonization, leading to pneumonia.

Finally, prolonged use of histamine H2-receptor antagonists for over 2 years may lead to vitamin B12 malabsorption and deficiency.Now, cimetidine also has additional anti-androgenic effects and could cause gynecomastia, galactorrhea, and alopecia.

On the other hand, famotidine can also cause seizures and QT prolongation in clients with renal disease, and very rarely, clients may develop hypersensitivity reactions like toxic epidermal necrolysis and Stevens-Johnson syndrome.

As far as contraindications go, histamine H2-receptor antagonists should be used with caution during pregnancy and breastfeeding.

Caution should also be taken in children under 16 years of age and elderly clients. Cimetidine and famotidine should also be used with caution in clients with hepatic diseaseIn addition, cimetidine requires dose adjustment in clients with renal disease, as it can decrease renal excretion of zand increase its blood levels.

Regarding interactions, cimetidine is a strong inhibitor of the cytochrome P450 enzyme in the liver. These enzymes are responsible for the metabolism and elimination of a variety of medications and toxins from our body.

So, if cimetidine is taken with certain medications, such as benzodiazepines, warfarin, beta-blockers, carbamazepine, phenytoin, or sulfonylureas; cimetidine could reduce their rate of elimination and cause them to build up in the body.Now, before administering histamine H2-receptor antagonists, be sure to obtain a baseline assessment of your client, including vital signs, neurological status, and gastrointestinal symptoms, like diarrhea and constipation; as well as the presence of any abdominal tenderness, distension, rebounding, or guarding.

Then, review any recent diagnostic information, including renal and hepatic function, ECG, and vitamin B12 level. If your client is diagnosed with an ulcer, review their radiologic or endoscopic results.

Then, be sure your client understands why their medication is prescribed and the recommended length of treatment. Alright, if a client with gastroesophageal reflux disease is prescribed cimetidine, teach them that their medication is most effective if taken before or with meals.

On the other hand, if cimetidine is prescribed for a duodenal or peptic ulcer, instruct them to take their medication at bedtime.

Also, let your client know that both gynecomastia and impotence may occur with this medication, that these are reversible, and if they think these symptoms are developing, that they should notify their healthcare provider.

While caring for a client taking any histamine H2-receptor antagonist, monitor your client for side effects and the therapeutic effects of decreased abdominal pain and other gastric symptoms.

Be sure to remind clients taking any histamine H2-receptor antagonist to increase their fluid intake as well as dietary intake of vitamin B12 during treatment.

Let your client know they should avoid smoking, alcohol, aspirin or other NSAIDs, caffeine, and spicy foods that may irritate the gastrointestinal tract.

Also, advise your client to notify their healthcare provider right away if they experience increasing abdominal pain, or blood in their vomit, stool, or urine; as well as other warning symptoms like confusion or hallucinations.

Finally, if a client is not able to take oral medication, you can administer an intravenous H2-receptor antagonist, such as famotidine.

After administering the medication, be sure to monitor your client closely for any cardiac arrhythmias that may occur.Alright, as a quick recap ….

Histamine H2-receptor antagonists are medications that help reduce the production of gastric acid, and can be used to treat conditions like gastroesophageal reflux disease, peptic ulcers, and Zollinger-Ellison Syndrome; as well as prevention of stress-induced ulcers.

These medications include cimetidine, famotidine, and nizatidine. Now, before administering histamine H2-receptor antagonists, nursing considerations consist of obtaining baseline assessment information and recent diagnostic data from your client.

After administration, be sure to let your client know about potential side effects, recommended dietary changes, and when to contact their healthcare