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Back: Are we giving our diabetic patients too much basal insulin?

By: Jim LaSalle, D.O.,FAAFP

Over the past several years there has been a push for PCP’s to move more quickly to initiate insulin therapy.  The ADA thought so much of this idea that they made it a part of their guidelines. 

Yet, with this paradigm shift there has been very little education on the “how to” aspect of this maneuver.  This has left many PCP’s in a lurch in determining how much and what insulins are appropriate.

Initiating basal insulin therapy in poorly controlled patients with type 2 diabetes on 2 OAD’s is very simple.  You start with a basal insulin and titrate until fasting plasma glucose levels are in the targeted range (80 mg/dl to 120 mg/dl).  Insulin selection is based on your desire to use human or analog insulins.  This choice has become increasingly easy as analog insulins continue to separate themselves from human insulins.  The recent 4-T Trial demonstrated the benefits of analog insulin therapy over human insulins by getting more subjects to the ADA target with fewer hypoglycemic episodes.  Hypoglycemia has become increasingly important since the ACCORD Trial findings two years ago.

The titration of basal insulin has many formulas that are both pragmatic and effective.  Yet, none ask the question how much is too much.  Clearly from a pathophysiologic perspective there is a point on the timeline of type 2 diabetes where further insulin intensification is necessary.  The uncertainty of this point makes it seductive and is often referred to as “individualized therapy”.  In reality, there needs to be some practical guidelines to assist PCP’s from over basalizing their patients.  Basal insulins should be peakless but in reality the more insulin that is given with one injection the greater the peak pharmacokinetically and hence the risk of hypoglycemia. Further, insulin in excess may be associated with weight gain and even mitogenicity.

Giving patients 100 units basal insulin or more may be indicated in some patients yet for most this is not the case.  In order to clarify this problem the following may be helpful in determining how much basal insulin is too much.

Basal insulin should be 50% of the total daily insulin requirement based on the 50/50 rule.  Therefore, calculating total daily insulin is important in determining how much basal insulin is too much. The experts tell us that the range for total daily insulin in insulin resistant diabetics is between 0.6 units/kg and 2.0 units/kg.  The more conservative range is between 0.6 and 1.2 units/kg, where as a more realistic range is between 1.0 and 2.0 units/kg/24 hr.  The experts vacillate about which range is correct so I will give you both and I have editorialized which I think is the most correct by calling it more realistic.

If we look at an example patient who is 100 kg in body weight then the total daily insulin requirement would be between 60-120 units/day in the conservative range to 100-200 units/day in the more realistic range.  If we then apply the 50/50 rule, the maximum basal insulin ranges from 60-100 units/day.  It is my opinion; the range of basal insulin should not exceed this range for most patients with type 2 diabetes.

Further, titration of basal insulin to 80 units per day and failure to control FPG between 80-120 mg/dl signals the need for insulin intensification.  The options at this point include basal bolus therapy vs mix insulin therapy up to three times daily or referral to a diabetic specialist that would include a CDE, diabetologist or an endocrinologist.

In summary, the maximum dose of basal insulin should not exceed a predetermined level of insulin based on a unit per kilogram formula. Over basalization may be a detriment to the patient by failing to get them to A1C target in a timely fashion, exposing the patient to supra-physiologic doses of insulin and the potential for over stimulation of intracellular growth pathways thereby fostering mitogenesis and weight gain.  Further, higher doses of insulin change the pharmacology of insulin and increase the risk of hypoglycemia.

The following guidance should then become intuitive in primary care:

  • Basal insulin analogs should not exceed 0.6-1.0 unit/kg/day
  • When 0.8 units/kg/day has been achieved, the PCP should begin to contemplate further insulin intensification or referral to specialty care
  • Basal insulin analogs in excess of 60 units may not be peakless and may contribute to hypoglycemia
  • Basal insulin analogs are more likely to get patients to A1C goal and cause less hypoglycemia