Thank you for asking the query.
Some drugs are under evaluation for the purpose of delaying pre diabetes progression. But no other drugs match the safety profile and favourable data of Metformin (Glucophage). So as of now this is the only recommended and safe drug for this purpose.
Higher doses are proven to be more effective. You may start with a dose of 850mg once daily (in consult with your Doctor) then make it 850mg twice daily for maximum effect. You can also use 500mg twice daily which is more conservative.
But, you SHOULD couple this with diet control and aerobic exercise. It is never later to start an exercise routine. This alone might be sufficient if done properly.
Please note, it is recommended that you should consult your Physician before starting the drug.
Hope this helps. Please feel free to ask follow-up questions if you have any. Thank you.