Module 2: H2RA Flashcards
True or False: Histamine H2 receptor antagonists are primarily used to treat allergic reactions.
False.
Multiple Choice: Which of the following is NOT a common indication for histamine H2 receptor antagonists? A) Zollinger-Ellison syndrome B) Allergic rhinitis C) Duodenal ulcers D) Gastroesophageal reflux disease
B) Allergic rhinitis.
What are common indications for famotidine 10 - 20 mg po
Self-medication for dyspepsia
What are common indications for famotidine 20 or 40mg PO
Duodenal ulcer - tx/prophylaxis
Benign gastric ulcer - Tx
GERD - Tx and maintenance of remission
Gastric hyper-secretion - tx (e.g. Zollinger-Ellison Syndrome = a digestive disorder causing overproduction of acid in the stomach
What are common indications for Ranitidine 75, 150mg
Self-medication for dyspepsia
What are common indications for Ranitidine high doses/prescription?
Duodenal ulcer - treatment/prophylaxis
Benign gastric ulcer – treatment
Gastric ulcer prophylaxis
GERD – treatment
Acid aspiration syndrome – prophylaxis
Hemorrhage from stress ulceration or recurrent bleeding - prophylaxis
What are the clinical outcomes/treatment goals of histamine H2 receptor antagonists?
Inhibited gastric acid secretion
Tx of acute bleeding in the upper GI tract = acid suppression promotes coagulation and platelet aggregation.
Describe the mechanism of action of histamine H2 receptor antagonists.
Compete with histamine for reversible binding with H2 receptors on stomach parietal cells
They reversibly inhibit the cAMP-dependent activation of H+, K+-ATPase (the proton pump) that pumps hydrogen ions into the gastric lumen.
H2Ras reduce the basal, nocturnal and stimulated gastric acid secretion in proportion to dose with less effect on stimulated secretion
What are the pharmacokinetic considerations of taking Histamine H2 Receptor Antagonists?
A: Rapidly absorbed orally with bioavailability 40-70%. Ranitidine undergoes first pass metabolism.
D: Low plasma protein binding.
M: Famotidine = 30-35% metabolized to an active metabolite. Ranitidine = 70% excreted unchanged in urine; metabolites may be active
E: Mainly excreted in urine; metabolites may be active.
True or False: Histamine H2 receptor antagonists must be taken with food.
False: Taken without regard to meals
What are pediatric considerations for H2 receptor antagonsis?
Increased risk for development of acute gastroenteritis and community-acquired pneumonia. Routine use in neonates associated with increased mortality and risk of infection.
Can H2 receptor antagonists be taken in pregnancy and during lactation?
Yes.
Can famotidine and ranitidine be taken with renal impairment?
With adjusted dosage
Can famotidine and ranitidine be taken with hepatic impairment?
Yes - no dosage adjustment required.
What are significant adverse reactions associated with H2RAs?
CNS: agitation, confusion, delirium (>60 and liver and kidney impairment increases chances)
Necrotizing enterocolitis in VLBW neonates
Cardiac effects and can cause prolonged QT.
What is the concern with Vit B12 and H2 receptor antagonists?
H2 receptor antagonists can reduce absorption of vitB12, thus decresing serum levels.
What are common expected side effects of H2 receptor antagonists?
CNS: Headache, Drowsiness, Dizziness
GI: Nausea, vomiting, constipation and diarrhea
What are 2 general drug interaction considerations for H2 receptor antagonists?
Reduced absorption of drugs requiring gastric acidity.
H2RAs are substrates for P-glycoprotein (use P-glycoprotein transporter for absorption, excretion and other activities which can lead to changes in the effects of other drugs on the body)
What are 2 ranitidine specific drug interaction considerations?
Ranitidine - can increase drug levels by competing for renal tubular secretion.
Ranitidine inhibits CYP2D6 and 3A but d/t weaker binding, interactions are rare.
What are the risks to long-term gastric acidity inhibition?
May enhance the survival of ingested organisms = increase risk for infection.
- H2RAs assoc with 50% increase risk for C. Diff (lower risk than with PPI)
- Increased risk of community and hospital-acquired pneumonia
Rebound increase in basal and stimulated gastric secretion may begin within 24 hours after d/c of 4 weeks of chronic therapy.
Treatment with H2RAs could mask what underlying causes?
CVD or GI malignancy
How quickly does tachyphylaxis (acute tolerance) occur with H2RA’s?
2 days - 2 weeks after first dose. Manifests as loss of acid inhibitory efficacy.
What is onset of action, peak and duration for Famotidine?
Onset of Action:
Oral- within 1 hour
Peak effect: Oral - within 1- 3 hrs (dose-dependent)
Duration: IV, Oral - 10-12 hours
What is the peak and half-life for ranitidine?
Peak: 2-3 hours
Half-life: 2-3 hours
What are general parameters for monitoring protocols with GI related meds?
Establish comprehensive monitoring protocols for renal function, electrolyte levels, and cognitive effects is essential, with dosage adjustments made to optimize treatment and minimize risk.
Monitor GI symtoms
May need to monitor pH levels (e.g Zollinger-Ellison syndrome)
