Mrsa infections symptoms and conditions

My son was given this medication for MRSA staph infection, in addition to Rifampin 300mg, and other medication he has had before. This is his 4th outbreak so they were trying to get aggressive with this treatment.

Yesterday, Day 4 (although he hadn't been taking his medication faithfully as he should have been) he developed a rash on the side of his tummy. Then today, it started spreading sporadically on his back, his knees are red & swollen, and his hands feel swollen to him as well. Since both these medications are new to us, and it's a Sunday, I'm having him stop both the SULFAM / TRIMETH, and the Rifmpkin until I can speak with a doctor tomorrow.

Looks like other people have had similar, and worse side effects such as his.