Why not try passing your parameters  in an XML document? Maybe have a simple XML
schema for your parameter passing, perhaps something like this:

<query>
<rxm_number>...</rxm_number>
<facility>...</facility>
...
</query>

You get the idea. It involves a more complicated parameter passing structure.
But it can be useful. You could simply pass the XML string  and then decode the
string into a document  to get the parameters for the query. You could also add
things like a type attribute  to a node to indicate that it's a date or a number,
among other things.