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 of acid ingestion
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 of acid indigestion
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. IM dose of ranitidine rapidly and almost completely absorbed.
D: Low plasma protein binding: 15-20% for famotidine, 10-19% for ranitidine.
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.
What is the pharmacologic category of famotidine and ranitadine?
Histamine-2 (H2) receptor antagonist
Can famotidine and ranitidine be taken with renal impairment?
Famotidine: CrCl<50ml/min: Administer 50% of usual dose or continue with regular dose and interval at every 36-48 hours.
Ranitidine: CrCl<50ml/min: Decrease dose by 50%. 150mg q24Hr recommended.
Can famotidine and ranitidine be taken with hepatic impairment?
Yes.
Child-Turgotte-Pugh Class A-C: IV, Oral: no dosage adjustment necessary.
What are common significant adverse reactions associated with famotidine and ranitidine?
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?
Headache (up to 17%)
Somnolence (state of drowsiness or strong desire to sleep) (up to 2%)
Dizziness (up to 5%)
Nausea, vomiting, constipation and diarrhea (1-2%)
What are 2 general drug interaction considerations for H2 receptor antagonists?
Reduced absorption of drugs requiring gastric acidity.
H2RAs are substrates for P-glycoprotein in vitro (use P-glycoprotein transporter for absorption, excretion and other activities which can lead to change sin 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 are some monitoring parameters with H2RA use?
Liver enzymes
Occult blood with GI bleeding, S&S of peptic ulcer disease
When used for stress-related GI bleeding - measure the intragastric pH and try to maintain pH >4
When used for Zollinger-Ellison syndrome, monitor gastric acid secretion (goal: <10mEq/hour)
Renal function
Sexual function in men taking high doses
CBC
What is onset of action and duration for Famotidine?
Onset of Action:
Oral- within 1 hour
Peak effect: Oral - within 1- 3 hrs (dose-dependent); IV - within 30 mins
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.
