I've never seen single doses on line, and I buy both the dogs' and the cats' on line.

Keep in mind, if you buy 3 doses, the cost per dose is higher than if you buy a 6 pack. And a 6 pack will cost more, per dose, than a 12 pack.

If you know you are are going to use 6 doses, I' suggest you just get that.

I go a bit nutty with online buying an often set up a spread sheet to figure out which site has the best price.