I can't imagine it being $4500 unless that is per year, not per month. Most of the numbers I have seen for Copaxone have the total cost at around $2500 per month. So charging you a copay of $4500 would be a $2K markup and you paying 100%.

$4500 per year would be $375 per month, which would be 15% of $2500, which isn't an unusually high percentage for a high cost drug like Copaxone under some plans.