Loratadine(SCH 29851) is discovered as part of a search for a new antihistamine without effects on the central nervous system (CHS). SCH 29851 has antihistamine activity in the tests used with a potency at least comparable to most standards.[1]
In vivo
Loratadine exhibits a more pronounced inhibition of histamine wheal formation than placebo or chlorpheniramine maleate (p less than 0.003). Loratadine inhibited the response for the entire observation period between 1 and 24 h post-dose. [2]SCH 29851 at 80 mg/kg po in mice, a dose about 50 times its ED50 for blocking histamine-induced paw edema in the same species, potentiated the anticonvulsant effects of diazepam. At the high dose of 320 mg/kg po, about 80 times its ED50 for antihistamine effects, SCH 29851 potentiated the ability of high doses of ethanol and hexobarbital to induce loss of righting reflexes (LRR).[3]