I was totally befuddled by insulin when starting intern year. Luckily, we were required to do PEAC modules that cleared up a lot of confusing issues.
When should insulin be started?
Insulin is recommended when hemoglobin A1C >10% and REQUIRED when >10% and ketonuria or weight loss are present.
HOW exactly is insulin therapy started?
Insulin therapy will always consist of basal insulin (glargine, detemir, NPH) +/- sliding scale. Aim for a morning fasting glucose of 80-130 mg/dl. Start with 10 U and see how the patient responds. If the glucose is above goal, add 2 U every 3 days until the goal is met. If the glucose is >180 mg/dl, add 4 U.
What if a patient was already on medications for diabetes and then has to switch to insulin?
The non-insulin medications may be continued UNLESS they’re a sulfonylurea, a DPP-4 inhibitor, or GLP-1 agonist.
What if the patient has good morning fasting glucoses, but their A1C is still high?
The likely cause is hyperglycemia associated with eating. You now have two choices: change to twice-daily premixed insulin (usually basal + short-acting) OR add prandial insulin.
Premixed combination therapy is harder to individualize, results in more hypoglycemia, results in inferior glycemic control. If you go with prandial insulin, start with 4 U with the largest meal of the day and aim to control the pre-prandial glucose of the following meal, or bedtime glucose if you’re targeting dinner time, to <130 mg/dl.