Zyrtek and Astelin are both antihistimines and I think they should be
effective fairly soon if they are going to work.  Flonase can take
several weeks.  From what my doctors have told me, you should feel good
for at least 5 days before you stop an antibiotic, but of course you
should always finish the prescribed amount unless you have an adverse
reaction or change to another one.  

Kathyw

As long as your MD prescribed it for - 10 days?????
Always finish your Meds even if you are feeling better.

Mine started to work after 48 hours.

shirley