after having serious complications stomache wise with Metformin, my GP has changed my prescription to Metformin RD, I have gone through the interim period and i am using three tablets a day with each meal - originally I took 6 'ordinary'.
Good news - no more waking up and going to bed with stomache ache...
Bad News - levels are 3 times over what they should be consistantly (just tested and its 16.3 and I am in work trying to concentrate!!)
Customer helplines that use recorded menus that promise to put me through to the right person but never do - and being ill. Oh, and did I mention customer helplines :)
Even the maximum dose of metformin only reduces bg levels by between 1 and 2mmol/L so your big rise must be due mainly to other influences, are you possible harbouring a cold, bug or something perhaps as that can often but not always increase bg levels. Have you changed your diet at all as this can make a big difference too?