Dog’s allergy

My dog had a sprain in his leg and the Vet gave me liquid Metacam (meloxicam) , it’s an anti-inflammatory. The first day I gave it to him, I noticed him licking his paws. Then I skipped a day. Then I gave it to him again and he was licking his back paws all day and night. I took him for the same amount of walks he normally gets but short ones as the Vet told me and he was fine. Then he started licking his back paws again. This time when he was licking them, I heard him cry a little so I took a closer look and this is what I saw:

http://farm4.static.flickr.com/3354/3446800574_b24dea5b15_o.jpg

It’s not bleeding. It just looks like it was inflamed and he was chewing.
Do you think it’s an allergic reaction to the anti-inflammatory? Or did something get in his paw. There is nothing there right now, I looked closely but this one paw is raw and pinkish. I will need to take him to the Vet tomorrow. And of course I’m not giving it to him anymore. For now.
Thanks for your help
I put an E-collar on him so he doesn’t chew it for now.