Can one metformin tablets at night and 30 units of humlin insulin in the morning good for one, or can it cause diabetic coma?

Not likley: It depends on your sugars honestly. If you are not what we call a brittle diabetic then you will be just fine. Monitor your sugars closely.

Depends: Diabetic coma usually is due to prolonged markedly elevated blood sugar. Coma can also occur with too low a blood sugar often from too much insulin. Therefore if the patient takes too little or too much insulin, coma can ensue. Metformin alone will not drop the blood sugar too low however. Without knowing more facts the above dosage of medication can be right, too much or too little.