"The usual dose is 2.5 mg/lb BID[SUP]1 ,12 [/SUP] but this can be doubled if it doesn’t seem to be working well. Because it is used in rats mainly for Mycoplasma, it should be given for a minimum of 6 weeks at a time, and is safe for very long term use. I recommend older rats be put on a treatment for myco, either doxy or Baytril, for the rest of their lives."
Please wait for another, more experienced rat keeper to give input though, I am only linking this as reference material that I was able to find. I do not have personal experience medicating rats on my own and have no personal advice to offer.
There is a link under one of the sticky notes posts that take you to a page with doage instructions.It's under the myco and resp heading. Doxy is what they put my girls on but they gave me a liquid. Were you able to find doxy pills without an rx and if so where can I find them?