H2 blockers are sometimes called H2 receptor antagonists, or H2RAs. They reduce the amount of acid that the stomach produces.H2 blockers can treat or prevent a number of health problems, including: heartburn GERD duodenal and gastric ulcers upper gastrointestinal bleeding gastric hypersecretory diseases, such as Zollinger-Ellison syndrome Cimetidine Cimetidine (Tagamet, Leader Heartburn Relief) comes in prescription, OTC, injectable, and IV forms. A doctor can advise about the most effective type for each person. It is important to follow directions for use carefully. The right dosage depends on a person’s age, whether they are taking any other medications, and the form of the drug. Older adults should avoid taking this medication, or use it with extreme caution. It may worsen or cause periods of confusion. People with kidney or liver disease should consult a doctor before using Tagamet. Some common side effects include: headaches drowsiness joint or muscle pain breast swelling and tenderness, in anyone dizziness confusion in elderly people, people with dementia, and those who are critically ill In some cases, people may also experience: a rash an allergic reaction production of breast milk trouble urinating pancreatitis a kidney infection Nizatidine Nizatidine (Axid, Tazac) comes as an oral solution or capsule. The right dosage depends on a person’s age, their symptoms, and the form of the drug. A person should consult a doctor before taking it. Like other H2 blockers, this medication may not be suitable for people with disorders of the kidneys or liver. A doctor or another healthcare professional can offer specific guidance. Some common side effects include: congestion, a runny nose, and similar symptoms, which are more common with Axid than with other H2 blockers a rash drowsiness irritability anxiety vomiting diarrhea a fever On rare occasions, a person may experience more serious side effects, including: hepatitis anemia jaundice chest pain impotence seizures a rapid heart rate a severe allergic reaction Famotidine Famotidine (Fluxid, Pepcid) comes in prescription and nonprescription oral formulas and as an IV infusion. A doctor or another healthcare professional can recommend the right dosage, based on the person’s symptoms, age, kidney function, and overall health. Side effects can include: diarrhea dizziness nausea a loss of appetite Rarely, people experience more severe side effects, including: conjunctivitis, also called pink eye hepatitis depression confusion seizures severe allergic reactions Stevens-Johnson syndrome, a potentially life threatening skin disorder Dosage of H2 blockers For the best results, a person should take H2 blockers orally once a day. The best time to take a daily dose of H2 blockers is before bedTrusted Source. If a person takes the more common twice daily doses of H2 blockers, they should take the first dose in the morning and the second dose in the evening. General side effects All four approv

1. H2 antagonist
MEDICINAL CHEMISTRY
By
Miss. Wagh hrutuja
ASSISTANT PROFESSOR
Lokmanya tilak institiute of pharmaceutical sceinces , pune

2. CLASSIFICATION OF H2 ANTAGONIST

3. Mode of action

4. Cimetidine
• 1-cyano-2-methyl-3-[2-[(5-methyl-1H-imidazol-4-yl)methylsulfanyl]ethyl]guanidine
• Cemetidine have 60 -70 % bioavailability. Plasma half life is about 2 hours,
• Cimetidine hydrochloride is a white crystalline powder, soluble in water, and
sparingly soluble in ethanol.
• It is a H2-receptor antagonist that not only inhibits gastric acid secretion, but also
prevents other actions of histamine mediated by H2-receptors. It is used in the
treatment of peptic ulceration. C
• imetidine has a weak antiandrogenic effect. Gynaecomastia may occur in patients
treated for a month or more.
• Uses:
• Benign gastric ulcer, HERTBURN, GERD, DUODENAL ULCER, EROSIVE ESOPHAGITIS,
GASTRIC ULCER AND PATHOLOGICAL HYPERSECRETORY CONDITION.

5. SAR Cimetidine
• Structure of the drug should closely resemble to the structure of histamine.
• Imidazole ring is maintained for affinity at H2 receptor site.
• Substitution at C-4 site helps in H2-selectivity of the drug.
• Sulfur atom increases potency than nitrogen or oxygen atoms.
• Replacement of N-cyanoamino group with nitromethylene increase the potency.
• Guanidines with electron withdrawing groups substitutions have decreased basicity
than guanidine.
• Replacement of imidazole ring with other aromatic rings gives other useful products.
[1]
•

6. Synthesis of Cemetidine

7. Famotidine
• Properties and uses:
• Famotidine is a white or yellowish-white crystalline powder or crystals, very slightly
soluble in water, soluble in anhydrous ethanol and glacial acetic acid, but practically
insoluble in ethyl acetate.
• It acts as a competitive, reversible H2-antagonist with a slow onset of equilibrium.
• This type of blockade is called nonequilibrium antagonism.
• Uses: the treatment of duodenal and gastric ulcers, Zollinger–Ellison syndrome,
and heart burn.

8. Ranitidine
• Properties and uses:
• Ranitidine hydrochloride is a white or pale yellow crystalline powder,
soluble in water, slightly soluble in anhydrous ethanol and methylene
chloride.
• In Ranitidine, the imidazole ring of cimitidine was replaced by furan in
conjugation with some rearrangement of the terminal functionality; the
substituted guanidine group has been isosterically modified by utilizing
a nitromethenyl moiety to basicity.
• It is used in the treatment of duodenal ulcer, gastric ulcer, and
pathological hypersecretory conditions.

9. side effect
• People with kidney or liver disease should consult a doctor before using Tagamet.
Some common side effects include:
• Headaches , trouble urinating
• pancreatitis
• drowsiness
• joint or muscle pain & an allergic reaction
• breast swelling and tenderness, in anyone
• dizziness
• confusion in elderly people, people with dementia, and those who are critically ill
• In some cases, people may also experience:
• a rash & a kidney infection
• production of breast milk