H2 Receptor Blocker Drugs

The Most Decent Acid Reducing Drugs 

Reasons Why I am Using the title decent for H2 receptors blockers over the other acid reducing drugs Like PPIs and Acid Neutralizing agent (like NaoH) are pretty obvious in the article go through full article and You will find the reason.

Agents Included In H2 Receptors Blockers

Cimetidine (Banned due to Aplastic anemia association) , Famotidine, Ranitidine, and Nizatidine.  

Pharmacokinetics:

All agent except Nizatidine extensively go through first pass effect and show bio-availability of about 50 %. Nizatidine has little first pass effect.  Goes through both renal and hepatic elimination. Dose Reduction is required in moderate to severs renal insufficiency and same with hepatic patients.

Route of Administration and Dosage

Cimetidine:-Parenteral 200mg/2ml , Oral Liquid 300mg/5ml and Oral tablet dosage form 400-800mg. (But don’t use this banned drug)

Ranitidine: -Parenteral 1-25mg/ml, tablets 75-50-300.

Famotidine: -IV bolus, Tablets 10-20mg, gel-caps and suspension 40mg/5ml.

Nizatidine: - Tablets 75 mg tabs and Capsules 150-300 mg.

Cautions in Parenteral Administration

Main thing to be cared about when administering H2 Receptor blockers is that they should be administered with slow IV bolus rate (plunger of injection should not be pressed at one)  and a slow iv infusion rate. The main reason is rapid IV administration cause sever cardiac event which arise from the action of these drug on Histamine receptor on heart may be fetal for cardiac patients. Although the selectivity of these drug for H2 receptors is almost 100 % but there is negligible selectivity for others receptors too which cause this problem.    

Pharmacodynamics

The H 2  antagonists exhibit competitive inhibition at the parietal cell H 2  receptor and suppress basal and meal-stimulated acid secretion in a linear, dose-dependent manner. They are highly selective and do not affect H1  or H3  receptors. The volume of gastric secretion and the concentration of pepsin are also reduced. On two ways H2 receptor blockers reduce acid secretion first through blocking H2 receptors and secondly by diminishing the effect of gastrin on gastrin receptors in the presence of H2 receptor Blockers.

Special Pharmacodynamics information is they reduces nocturnal (Night) acid secretion (which is mainly due to histamine) well compare to meal stimulated acid secretion. Because Meal stimulated acid secretions is dependent on acetyl-choline, gastrin as well as histamine.

(The Most Decent Drugs)

The title decent which I have given to this class of drug compare particularly to PPIs is that they are safe for prolong use without any potential risk of Hyperplasia of Parietal cells. As PPIs block proton pumps on parietal cells they low acid secretion but at the same time gastrin is releasing and developing higher and higher in concentration, leading to potential cause for Hyperplasia of parietal cells which may lead to carcinoma. Other reason which are concerned is that PPIs prolong use leads to weak bones which may be a bad experience for geriatric patient as PPIs drastic use is among the older age. And due to the above reasons they are given after for use of PPIs in chronic conditions.

Clinical Uses of H2 Receptor Blockers

1)Peptic Ulcer 2) Non-Ulcer Dyspepsia 3) Gastroesophageal Reflux Disease (GERD) 4) Stress Related Ulcer  

Adverse Drug Reactions

Except cimetidine (which is banned drug now) others H2 receptor blockers are mostly well tolerated have no side effect except for 3% patients.  Cimetidine has the notorious side effects gynecomastia , impotence and galactorrhea which is due to tendency of Cimetidine inhibits binding of dihydro-testosterone to androgen receptors, inhibits metabolism of estradiol, and increases serum prolactin levels.  The ADR due to which Cimetidine is banned is its tendency of causing aplastic anemia.