Class 5 and the deceptive similarity standard
Pharmaceutical preparations sit in Class 5. Courts and the Registry apply a stricter standard of deceptive similarity to medicinal marks than to ordinary goods, because confusion between two drug names carries a public health consequence rather than a commercial one.
The practical effect is that marks which would coexist comfortably in another class are refused in Class 5. Names built from the same active ingredient stem, which is a common industry convention, sit particularly close to each other and need careful clearance rather than an assumption that the convention protects them.
INN stems and what cannot be monopolised
International Non-proprietary Name stems are the common syllables that identify a drug class. They are deliberately available to the whole industry, and a mark that consists of or closely follows an INN stem is weak - both to register and to enforce.
A brand built on a distinctive prefix attached to a recognised stem is the usual compromise, and the strength of the mark lives in the prefix.
Export markets and the limits of an Indian registration
A trademark registration is territorial. An Indian registration protects you in India and nowhere else, which matters for a Hyderabad pharma or API business selling into regulated export markets.
The Madrid Protocol allows an international application based on an Indian application or registration, designating multiple countries in one filing. It is filed through the Indian registry as office of origin and is materially cheaper than filing country by country.