Question

Famotidine contains:

• A. Thiazole ring
• B. Imidazole ring
• C. Pyrrole ring
• D. Furane ring

Answer 1

The Correct Option is A

The correct option is (A): Thiazole ring.

Answer 2

Famotidine belongs to the H2-receptor antagonist family used to reduce stomach acid, alongside cimetidine, ranitidine and nizatidine. Each drug in this family is built around a different heterocyclic ring attached to a guanidine-type side chain, and that ring is exactly what the question is asking about.

1. Thiazole ring: Famotidine's core structure is a guanidinothiazole, a thiazole ring (a five-membered ring with one sulfur and one nitrogen) carrying a guanidine group, connected through a sulfur-containing side chain to a sulfamoyl-amidine end group. This thiazole core is the defining structural feature that separates famotidine from the other H2 blockers.
2. Imidazole ring: The imidazole ring is the defining heterocycle of cimetidine, the first H2 antagonist developed, not famotidine. Confusing the two is a common mix-up because both drugs work on the same receptor.
3. Pyrrole ring: A pyrrole ring is a five-membered ring with a single nitrogen and no sulfur. None of the major H2-receptor antagonists, including famotidine, are built on a pyrrole core.
4. Furane ring: The furan ring, an oxygen-containing five-membered ring, is the signature heterocycle of ranitidine, another drug in the same class. It is not part of famotidine's structure.

Since famotidine is built on a guanidinothiazole scaffold, unlike cimetidine's imidazole or ranitidine's furan ring, the thiazole ring is the one it contains.

The correct answer is Thiazole ring.