<Li> Rupatadine (Alergoliber) </Li> <P> The H receptor inverse agonists include: </P> <Ul> <Li> Cetirizine (does not cross the blood--brain barrier) <Ul> <Li> Levocetirizine </Li> </Ul> </Li> <Li> Desloratadine (does not cross the blood--brain barrier) </Li> <Li> Pyrilamine (crosses the blood--brain barrier; produces drowsiness) </Li> </Ul> <Li> Cetirizine (does not cross the blood--brain barrier) <Ul> <Li> Levocetirizine </Li> </Ul> </Li>

Which of these is the best definition for histamine