What Causes Dry Skin When I Am Having Mupirocin For Impetigo?

I was just diagnosed with impetigo on my chin and was prescribed mupirocin to put on it 3 times per day. The problem is, the skin is getting so dry and crusty. Is this normal... is it a sign of the antibiotic working? Also, can I put some sort of moisturizer on it when it gets dry?