WordNet records no synonym and no antonym for pheniramine. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an antihistamine used in preparations to treat allergies and respiratory infections; used to treat rhinitis and skin rashes and pruritus
Synonyms, antonyms and the broader and narrower relations for pheniramine come from Princeton University’s WordNet. Full sources and licences.