Medical grade does not only include the additives, but the manufacturing and packaging process as well.
As far as additives are concerned, it can't contain anything that is toxic or hazardous.
You could start by comparing your PGA to Surgicryl a PGA absorbal suture.
I think there is another PGA product called Kurdux (kurdex, curdex, curdux, somthing like that) used for tissue scaffolding, but I've never used it and don't know that much about it - including how to spell it.