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H2 receptor blockers

PPIs versus H2 antagonist

Treatment of bleeding peptic ulcers : A meta-analysis of 21 randomized controlled trials evaluating proton pump inhibitors for bleeding ulcers (with or without endoscopic therapy) found a significant and consistent reduction in the risk of rebleeding. In contrast, studies on H2 antagonists have generally produced disappointing results. A meta-analysis concluded that there was a possible minor benefit with intravenous H2 antagonists in bleeding gastric ulcers but no benefit with duodenal ulcers. The relative efficacy of the proton pump inhibitors may be due to their superior ability to maintain a gastric pH at a level above 6.0, and thus protect an ulcer clot from fibrinolysis.
cimetidine (Tagamet ®) famotidine (Pepcid ® )
nizatidine (Axid ® ) ranitidine (Zantac ® )

cimetidine (Tagamet ®)   top of page

Mechanism of action:
Cimetidine competitively inhibits the action of histamine at the histamine H2-receptors of the parietal cells and thus is a histamine H2-receptor antagonist.

Cimetidine is not an anticholinergic agent. Studies have shown that cimetidine inhibits both daytime and nocturnal basal gastric acid secretion. Cimetidine also inhibits gastric acid secretion stimulated by food, histamine, pentagastrin, caffeine and insulin.


Active ulcer
: Oral: 800 mg orally at bedtime or 300mg orally four times daily or 400 mg orally twice daily. IM/IV: 300mg every 6 hours or 37.5 mg/hr continuous infusion.

Active bleed: 37.5 mg/hr continuous IV (maximum 2400mg/day).
Maintanance (duodenal ulcer prophylaxis): 400mg orally at bedtime.

Gastric hypersecretory conditions: 300 to 600mg every 6 hours.

Renal Dosing: >40 ml/min: no change || 20-40 ml/min: give usual dose q8h or give 75% of usual dose. || 0-20 ml/min: Usual dose q12h or give 50% of usual dose.

famotidine  (Pepcid ® )  top of page

Dosing- Adults:
Duodenal ulcer: Oral: Acute therapy: 40 mg/day at bedtime for 4-8 weeks; maintenance therapy: 20 mg/day at bedtime

Helicobacter pylori eradication (unlabeled use): 40 mg once daily; requires combination therapy with antibiotics

Gastric ulcer: Oral: Acute therapy: 40 mg/day at bedtime

Hypersecretory conditions: Oral: Initial: 20 mg every 6 hours, may increase in increments up to 160 mg every 6 hours

GERD: Oral: 20 mg twice daily for 6 weeks

Esophagitis and accompanying symptoms due to GERD: Oral: 20 mg or 40 mg twice daily for up to 12 weeks

Patients unable to take oral medication: I.V.: 20 mg every 12 hours

Dosing adjustment in renal impairment: Clcr<50 mL/minute: Manufacturer recommendation: Administer 50% of dose or increase the dosing interval to every 36-48 hours (to limit potential CNS adverse effects).

Supplied:
Gelcap (Pepcid® AC): 10 mg
Infusion [premixed in NS] (Pepcid®): 20 mg (50 mL)
Injection, solution: 10 mg/mL (4 mL, 20 mL, 50 mL) [contains benzyl alcohol]
Injection, solution [preservative free] (Pepcid®): 10 mg/mL (2 mL)
Powder for oral suspension (Pepcid®): 40 mg/5 mL (50 mL)
Tablet: 10 mg [OTC], 20 mg, 40 mg
Pepcid®: 20 mg, 40 mg [film coated]
Pepcid® AC: 10 mg, 20 mg
Tablet, chewable (Pepcid® AC): 10 mg [contains phenylalanine 1.4 mg/tablet; mint flavor]
Tablet, orally-disintegrating (Fluxid™): 20 mg, 40 mg [cherry flavor]

Famotidine is becoming the preferred agent in many intensive care units. Unlike cimetidine, it has no significant hemodynamic effects nor does it alter hepatic drug metabolism and in preference to ranitidine, it has no adverse effects on platelet production. This favorable safety profile combined with its profound inhibitory effect on gastric acid secretion and its q12h-dosing schedule has made this H2 antagonist exceedingly popular for use as an agent for stress ulcer prophylaxis.

nizatidine  (Axid ® )  top of page

Dosing- Adults:
Duodenal ulcer:
Treatment of active ulcer: 300 mg at bedtime or 150 mg twice daily
Maintenance of healed ulcer: 150 mg/day at bedtime

Gastric ulcer: 150 mg twice daily or 300 mg at bedtime

GERD: 150 mg twice daily

Meal-induced heartburn, acid indigestion, and sour stomach: 75 mg tablet [OTC] twice daily, 30 to 60 minutes prior to consuming food or beverages

Helicobacter pylori eradication (unlabeled use): 150 mg twice daily; requires combination therapy

Dosing adjustment in renal impairment:
Active treatment:
Clcr 20-50 mL/minute: 150 mg/day
Clcr<20 mL/minute: 150 mg every other day

Maintenance treatment:
Clcr 20-50 mL/minute: 150 mg every other day
Clcr<20 mL/minute: 150 mg every 3 days

Supplied
Capsule (Axid®): 150 mg, 300 mg
Solution, oral (Axid®): 15 mg/mL (480 mL) [bubble gum flavor]
Tablet (Axid® AR): 75 mg

ranitidine (Zantac ® )  top of page

Dosing- Adults:
Duodenal ulcer: Oral: Treatment: 150 mg twice daily, or 300 mg once daily after the evening meal or at bedtime; maintenance: 150 mg once daily at bedtime

Helicobacter pylori eradication: 150 mg twice daily; requires combination therapy

Pathological hypersecretory conditions:
Oral: 150 mg twice daily; adjust dose or frequency as clinically indicated; doses of up to 6 g/day have been used

I.V.: Continuous infusion for Zollinger-Ellison: 1 mg/kg/hour; measure gastric acid output at 4 hours, if >10 mEq or if patient is symptomatic, increase dose in increments of 0.5 mg/kg/hour; doses of up to 2.5 mg/kg/hour have been used

Gastric ulcer, benign: Oral: 150 mg twice daily; maintenance: 150 mg once daily at bedtime

Erosive esophagitis: Oral: Treatment: 150 mg 4 times/day; maintenance: 150 mg twice daily

Prevention of heartburn: Oral: Zantac® 75 [OTC]: 75 mg 30-60 minutes before eating food or drinking beverages which cause heartburn; maximum: 150 mg in 24 hours; do not use for more than 14 days

Patients not able to take oral medication:
I.M.: 50 mg every 6-8 hours
I.V.: Intermittent bolus or infusion: 50 mg every 6-8 hours
Continuous I.V. infusion: 6.25 mg/hour

Elderly: Ulcer healing rates and incidence of adverse effects are similar in the elderly, when compared to younger patients; dosing adjustments not necessary based on age alone

Dosing adjustment in renal impairment: Adults: Clcr<50 mL/minute:
Oral: 150 mg every 24 hours; adjust dose cautiously if needed
I.V.: 50 mg every 18-24 hours; adjust dose cautiously if needed

Hemodialysis: Adjust dosing schedule so that dose coincides with the end of hemodialysis

Administration
Ranitidine injection may be administered I.M. or I.V.:
I.M.: Injection is administered undiluted.
I.V.: Must be diluted; may be administered IVP or IVPB or continuous I.V. infusion.

IVP: Ranitidine (usually 50 mg) should be diluted to a total of 20 mL with NS or D5W and administered over at least 5 minutes.
IVPB: Administer over 15-20 minutes.

Continuous I.V. infusion: Administer at 6.25 mg/hour and titrate dosage based on gastric pH by continuous infusion over 24 hours

Supplied
Capsule, as hydrochloride: 150 mg, 300 mg
Infusion, as hydrochloride [premixed in NaCl 0.45%; preservative free] (Zantac®): 50 mg (50 mL)
Injection, solution, as hydrochloride (Zantac®): 25 mg/mL (2 mL, 6 mL, 40 mL)
Syrup, as hydrochloride: 15 mg/mL (10 mL) [contains alcohol 7.5%; peppermint flavor]
Zantac®: 15 mg/mL (473 mL) [contains alcohol 7.5%; peppermint flavor]
Tablet, as hydrochloride: 75 mg [OTC], 150 mg, 300 mg
Zantac®: 150 mg, 300 mg
Zantac® 75: 75 mg
 

Reference(s)

National Institutes of Health, U.S. National Library of Medicine, DailyMed Database.
Provides access to the latest drug monographs submitted to the Food and Drug Administration (FDA). Please review the latest applicable package insert for additional information and possible updates.  A local search option of this data can be found here.

Disclaimer

Listed dosages are for - Adult patients ONLY. PLEASE READ THE DISCLAIMER CAREFULLY BEFORE ACCESSING OR USING THIS SITE. BY ACCESSING OR USING THIS SITE, YOU AGREE TO BE BOUND BY THE TERMS AND CONDITIONS SET FORTH IN THE DISCLAIMER. GlobalRPH does not directly or indirectly practice medicine or provide medical services and therefore assumes no liability whatsoever of any kind for the information and data accessed through the Service or for any diagnosis or treatment made in reliance thereon.

David F. McAuley, Pharm.D., R.Ph.  GlobalRPh Inc.
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