About meclizinefirst generation h1 antagonist, piperazine derivative, antihistamine, antiemetic, antinauseant.mechanism of action of meclizinemeclizine produces antiemetic action by its central action on chemoreceptor trigger zone (ctz). it decreases the sensitivity of labyrinth apparatus which transmit stimuli to the ctz and stimulates the vomiting center. meclizine produces antivertigo action by decreasing the excitability of middle ear labyrinth. it blocks the conduction in the middle ear vestibular path ways. meclizine is a potent h1 receptor antihistaminic agent. it has anticholinergic activity also about vit b6physiological functions: it is involved as a coenzyme (pyridoxal phosphate) in metabolism of tryptophan, in several metabolic transformations of amino acids including transamination, decarboxylation & racemization. deficiency symptoms: peripheral neuritis, seizures, stomatitis, glossitis, anaemia, seborrhea like lesions.