I tend to give them both treatments separately if I can weeks apart otherwise days apart, I don't know the rule of thumb.

I use frontline every 4 weeks during the summer months and every 6 weeks during the winter months. De-wormer every 3 - 4 months. My previous cat was an outdoor cat.

I will treat the kittens every 6 to 8 weeks with frontline and de-worm every six months as they are indoor cats. Their treatment has been a lot more frequent than normal under veternarian supervision to both clean them and to prevent re-infestation.

Sue