I believe the poster is referring to one of the Regular insulins being given on a sliding scale. This is an outdated method of using insulin. My suggestion is to see an endo and get put on a regimen of basal and bolus (long acting and short acting) insulin and learn how to match your carbs to your insulin dose. You don't want to continue to have highs like that on a regular basis.
Yes, it is safe to take metformin and humulin together. In fact they can work very well together.
Humulin what? is it the combined 70-30?
I take humulin 70-30. My insulin is split into 2 doses a day. 1 in the morning about 20 minutes before breakfast and 1 in the evening about 20 minutes before dinner. I also need to count carbs and not eat too many. The insulin dose is adusted to ideally keep my blood sugar below 140 all the time.
Taking insulin after the bs is so high is not the optimal way to take it. The horse has already bolted. Instead the insulin should be taken to prevent the BS getting so high.
Your blood sugars are dangerously high at 250 - 300! I think you need a second opinion on how to handle this, if you are really only taking insulin in response to such high sugars instead of preventing them in the first place.