How long before Revolution goes bad? And can you mix it for larger dogs?

I have an old tube of Revolution, and I was curious how long that stuff lasts? Also if you can mix tubes of it, for a larger dog. Like 2, 5-10 lbs packages, for a 20 pound dog. Any help is appreciated. I would like to thank everyone that answered the question. I finally found the expiration date, and it expired 10/07, so thats almost a year past the date. So this definitely means I should dispose of it....right?

There should be an expiration date stamped on the crimping at the end of the tube. Yes - You can use 2 smaller tubes to make up the size difference.The best thing to do would just take your dog to the Vet and get a current prescription.Edit - Yes, that means you should dispose of it. Medications of any kind shouldn't be used after the expiration date - They can take 1 of 2 turns when they expire - 1) They lose their effectiveness or 2) They become Toxic

Yes you could mix the two.In fact i even buy the flea meds for large dogs,and half it,cause i have 3 small dogs....i save a lot buy doing that.It depends on the stamp on the pack.i just got some and there stamp says is good till 2009.XXX