Welcome to the site.
Well you see the first drug of choice for agitated depression
will be an anti depressant
but since an anti depressant will take around 2-3 weeks at least to reach steady state plasma levels and start producing it's controlling action over agitated depression therefore quite often an anxiolytic drug like a benzodiazepine
such as clonazepam
shall be added right from the start because these drugs have faster onset of action against agitation as they shall bring in the calming effect within 1 week of their use thereby allowing the chief anti depressant drug to take it's time to settle down in the body system and bring out it's action. Once the anti depressant starts producing it's action , say after 2-3 weeks then you may start to bring the person off the anxiolytic drug since they are used only for a short period.
So anti depressant is the first line drug in this condition where as one has to choose between an anxiolytic or seroquel
as an add on drug and between these two due to faster onset of action an anxiolytic like benzodiazepine shall be the first choice.
I hope this helps.
Wish you all the best.