Can Profender cause loose stools?

[Notfootball]

I followed your advice from my previous thread and got 2 beautiful rescue kittens. They are about 11 weeks old and had their first vaccinations at the weekend. They were also wormed, the vet used Profender. Pink cat already had loose stools 2 days before the vet visit which vet said could be down to worms. Now Blue cat has loose stools too. Luckily they are litter trained but they are trailing poo out of the tray on their paws and leaving pooprints everywhere plus the smell is phenomenal.

Could this be caused by the jab or the Profender? Is there anything I can do to help them or shall I just go back to the vet? They are happy, eating well, drinking well and running around like loons so they do not seem adversely affected.