What kind of worm? As Panacur doesnt do the tapeworm related to fleas.
I would give a drontal and do them regular, it doesnt sound like the owners are doing much if the cats live and eat at yours
![Crazy :Crazy:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/mad.gif)
Tablet wormers dont stay in the body like spot ons so safe to use regularly, some kittens are done every 2 weeks if infested
![sick :sick:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/sick.gif)
You'll also be pleased to hear that worms can hibernate in muscle tissue and migrate when they wish which is why regular worming is important
![Grin ;D](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/grin.gif)
You can get drontal online v.cheaply from VetUK, i'd do both of them
![Wink ;)](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/wink.gif)
Lots of rescues have links to vetuk that earn commission, so dont forget to use one of those!