Should you take your antihistamines twice a day if you feel that one intake doesn't cut it?

Should you take your antihistamines twice a day if you feel that one intake doesn't cut it?

Absolutely. Virtually all of the non-sedating antihistamines and also the H2 blockers are dosed twice a day. 
But I have one patient who's got autism. If she doesn't get three a day H1 blocker, she really declines mentally. But if she keeps her steady state up with the drug, it works great.