I would put him in a small yard for the time being (if he is still lame) and call the vet.
I have seen this when our mare had a flap of skin hanging off the back of her leg. We kept her in a small paddock and just waited for the wound to heal.
With your horse I'm not sure really what to do.. Just call your local vet for some advice I would suggest. And I don't think being of his meds for 1 day would affect him yet ; perhaps 3-7 days.
Hope It Helps!
"If you act like you've only got fifteen minutes, it'll take all day. Act like you've got all day and it'll take fifteen minutes." - Monty Roberts