<prompt> H1blocker with least sedative effect is -ChlorpheniraminePromethazineTerfenadineDiphenhydramine  <response>: Ans. is c i.e., Terfanadine Terfanadine is a second generation antihistaminics. Advantages of second generation Antihistaminics. o Higher H1 selectivity, no anticholinergic side effects. o Absence of CNS depressant propey o Additional antiallergic mechanism apa from histamine block. o No impairment of psychomotor performance driving etc. need not be contraindicated o No subjective effect, No sleepiness. Some patients complain of sedation, but the incidence is similar to placebo o Do not potentiate alcohol or benzodiazepene 