I know Revolution is very safe, but I hesitate to get the dog strength because they might need a dose of 0.01ml if they are little (200g), which is very difficult to do.
But, the cat tube has 0.75ml, so if the dose averaged out to 0.03ml a rat, it contains 25 doses.
The best way to use every drop of Revo is to get a 1cc syringe and a needle. Do not open the medication tube the normal way. Put the needle on the syringe and poke it through the plastic at the end of the tube of Revo. Draw up what you need for one dose, and remove the syringe, leaving the needle part in the tube of Revo. Dose your rat and then reattach the needle, drawing up more medication. Detach and medicate. Repeat. This way you can use up almost every last drop of medication.