Antihistamines may be given by various routes, including Oral (multiple—see table Oral H1 Blockers) Intranasal (azelastine or olopatadine to treat rhinitis) Ocular (eg, azelastine, emedastine, ketotifen, levocabastine, olopatadine, or pemirolast [not available in the US] to treat conjunctivitis) Cutaneous (eg, diphenhydramine, doxepin) Table Mast cell stabilizers Mast cell stabilizers block the release of mediators from mast cells.