I'm not sure if there are any serious side effects, other than the usual cold, flu-like symptoms, if taken in excess amounts. I would personally say that 500/125 mg is okay, but I would wait for a second opinion. I did a quick search on it, and found this:
"Amox TR-K CLV is an antibiotic that treats bacterial infections. Side effects of Amox TR-K CLV include nausea, vomiting, stomach pain and diarrhea. This medication is usually given once ever 12 hours." Also I found that you should eat a meal before taking the medication, something like yogurt or fruit.
Hope this helps.