Hi Paddypaws best advice do not put your cats or yourself at risk,ringworn doesnt hurt the cat but is a highly contagious inconvience. I have not used the intrafungal medication but do know that it makes poor puss feel awful.Previously they used a drug called Grisofulvin which was terrible,horrendous side effects,I took in a poor pregnant cat who had taken it,unprescribed and her kittens were born horribly deformed for this reason I vowed to use topical meds if I took in anything with ringworm.
Boots and bigger chemists sell a human anti fungal cream,its around £6 tube and totally safe for cats, it works a treat, the other thing which will help is sunshine. oops forgot to put name of cream hence moderation,its called DAKTARIN GOLD
The day will soon come when its safe to give this lad a big cuddle, and on the bright side he is safe and receiving treatment.
Incidentally my first rescue cat had ringworm and needed isolation
,until then I was a dog fosterer.