Famotidine decreases the production of stomach acid, and its pharmacologic activity is used in the treatment of acid-related gastrointestinal conditions. Famotidine is available both by prescription and over-the-counter (OTC). It is US Food and Drug Administration (FDA) approved and available through prescription for the treatment of duodenal ulcer, gastric ulcer, and gastroesophageal reflux disease (GERD) in adults and children, with a further indication for treatment of pathological hypersecretory conditions in adults. Famotidine is also FDA approved for over-the-counter treatment and prevention of heartburn due to gastroesophageal reflux in adults and pediatrics. Famotidine is used off-label for reducing gastrointestinal risks of NSAIDs. It is also used off-label for the treatment of refractory urticarial, prevention of stress ulcer in critically-ill patients and symptomatic relief of gastritis.
Famotidine is a competitive histamine H-receptor antagonist (H2RA) that binds to the H-receptors located on the basolateral membrane of the parietal cell in the stomach, effectively blocking histamine actions. Its pharmacologic activity results in the inhibition of gastric secretion by suppressing acid concentration and volume of gastric secretion. Famotidine inhibits both basal and nocturnal gastric acid secretion as well as reduces gastric volume, acidity, and secretion stimulated by food, caffeine, insulin, and pentagastrin.
Per famotidine's package insert, it is available in intravenous (IV) solution, oral suspension, and tablet formulations (10 mg, 20 mg, and 40 mg). The intravenous solution can be administered as an IV push over at least two minutes and as an IV infusion over 15 to 30 minutes. Over-the-counter formulations are available in gel capsules, tablets, and chewable tablets of 10 mg or 20 mg. The oral tablet is administered without regard to meals. The suspension formulation should be shaken vigorously before use. The over-the-counter tablet should not be chewed, and the dose may be taken 10 to 60 minutes before consuming food or drinks known to cause heartburn. Patients should not take over-the-counter famotidine for more than 2 weeks unless directed by their health care provider. Famotidine is metabolized by the hepatic cytochrome P450 enzymes, but it has a minimal inhibitory impact on other drugs metabolism. Per package insert, the following medications should not be used concurrently with famotidine: cefuroxime, dasatinib, delavirdine, neratinib, pazopanib, and risedronate.
The adverse effects of the intravenous formulation occur locally as it may irritate the injection site; however, the frequency has not been defined. Most common adverse effects include agitation (infants equal to 14%; adults less than 1%), headache (5%), dizziness (1%), diarrhea (2%), and constipation (1%). Due to central nervous system (CNS) adverse effects, longer dosing intervals or reduced doses may be used instead to adjust for the resulting longer elimination half-life of famotidine. An increased risk of developing community-acquired pneumonia and acute gastroenteritis have been linked to the use of famotidine as well as other gastric acid inhibitors in the pediatric population. Patients who use over-the-counter famotidine must notify their health care provider if they experience frequent chest pain, frequent wheezing particularly with heartburn, unexplained weight loss, stomach pain, heartburn more than 3 months, heartburn with lightheadedness, sweating, or dizziness. Over-the-counter famotidine must be discontinued if a patient’s heartburn continues and/or worsens, or if they use it for more than 14 days.
Famotidine is contraindicated for use by patients with serious hypersensitivity to famotidine itself or any component of the formulation. Cross-sensitivity of H2RAs has been observed; therefore, famotidine should not be administered to patients with a history of hypersensitivity to cimetidine. In addition, the over-the-counter tablets should not be used if the patient has trouble and/or pain when swallowing food, vomiting with blood, or bloody or black stools. The over-the-counter tablets should also not be used by patients who are allergic to other acid reducers, have renal impairment, or are currently taking other acid reducers.
Famotidine is substantially excreted by the kidney; thus, it may be useful for healthcare professionals to monitor renal function especially in elderly patients. A patient’s complete blood count (CBC), gastric pH and occult blood in patients with gastrointestinal (GI) bleeding should be monitored.
As famotidine is excreted mainly by the kidney, the risk of toxic reactions may be greater in patients with impaired renal function. Dose adjustment in patients who have moderate to severe renal impairment is necessary. Per famotidine's package insert, oral doses outside of FDA-approved doses of up to 640 mg per day have been given to adult patients with pathological hypersecretory states with no serious adverse outcomes. Cases of overdose are similar to those encountered in normal clinical experience. Treatment of an overdose should include removing unabsorbed medications from the gastrointestinal tract, the patient should be monitored accordingly, and supportive therapy provided. Famotidine is classified as pregnancy category B and should be used during pregnancy only if needed. Famotidine is present in breast milk, and the decision for a mother to breastfeed during therapy should be based on the balance of risk to the infants and treatment benefits to the mother. Compared to other H2RAs, famotidine exhibit one of the lowest concentrations in break milk and is thus, maybe one of the preferred agents in this setting.
The American Society of Health-System Pharmacists (ASHP) in 1999 released a guideline focusing on the prevention of stress ulcer in medical, surgical, respiratory, and pediatric intensive care unit (ICU) patients. Since then, and in recent years, the use of stress ulcer prophylaxis in a non-ICU setting, particularly in the general medical setting, have increased despite little to no evidence supporting its use. The use of acid-suppressive therapy (AST) is overused in hospital patients, with as many as 71% of patient's receiving treatment without an appropriate indication in the general medicine ward. Furthermore, a significant number of patients continue on acid-suppressive therapy when discharged from the hospital which can lead to increased medical cost and the risk of adverse drug reactions for patients. Health care professionals play an important role in enhancing patient's safety by minimizing the inappropriate use of AST. Physicians should carefully consider the need for AST in patients in the general medicine ward and pharmacist can communicate with physicians and ask about the unnecessary use of acid-suppressive therapy. Education about the proper use of acid-suppressive therapy in ICU settings per ASHP recommendations will help reduce its inappropriate use significantly.
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