Oh bless him. What about flea collars? They seem to be milder. I don't even know if they still exist, as my lot never had any flea treatment or fleas (being largely indoor cats until I moved here, but even then they did not encounter other cats).

Flea collars are ghastly, earlier cats got black lumps under them that I'm convinced were tumors.

We gave up dosing our two because it was such an ordeal for all concerned. They've been fine, despite being outdoor cats.