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Rapid acting insulins are used for mealtime management of blood sugars.  The insulin is given before a meal, with some clinicians telling patients “have a fork in one hand, and your insulin pen in the other!” Ideally the patient does their carb counting and calculates the dose of mealtime insulin based on their correction factor, as well as an insulin:carb ratio.  Because so many patients are unable to accurately count carbohydrates, clinicians offer a fixed dose for mealtimes along with a correction factor after the patient does a mealtime finger stick.


Insulin lispro is a rapid acting insulin formulation, where the original human insulin amino acid (B29). Lispro has an onset of action= 0.25 hours, with a peak = .5 to 1.5 hours.

Expect a duration of action around 2.5 hours.

Humalog® U-100 (Lispro) by Lilly, was approved in June of 1996. It is available as a vial andas a pen.  The vial is available as U-100 concentration.  The pen is available as both U-100 and U-200 pens.  The U-200 pen might be of value in patients that take higher doses of Humalog in that net absorption is reduced with increasing size of the subcutaneous depot.  The smaller size of the depot might lead to better and more predictable absorption.

  • Admelog® U-100 (Lispro) by Sanofi-Aventis, available in vials and pens, and is considered to be a biosimilar to Humalog. Since Admelog is not FDA approved as a generic, it cannot be automatically interchanged by the pharmacy without a new prescription from the provider.
  • Insulin Lispro Kwikpen® by Eli Lilly, is an” authorized generic” which was Eli Lilly’s response to Sanofi’s Admelog Solostar. Both vials and pens are now available.


Likes lispro, aspart is a rapid acting mealtime insulin that the amino acid sequence is changed to provide a more rapid response than our own regular insulin produces. Aspart has an onset of action= .25 hours, with a peak in 1-2 hours, and a duration of 3-5 hours.

Novolog® U-100  (Aspart) by Novo Nordisk, was approved in June 2000 and is available as vials and Flexpens.

Fiasp®, competitor of Novolog, also made by Novo Nordisk, approved in September 2017. Fiasp has vitamin B3, (niacinamide) which makes it more fast-acting.  Both Novolog® and Fiasp® contain insulin aspart and are priced the same.  Fiasp can be taken as much as 20 minutes after starting a meal, while other injected mealtime insulins are best taken 15-20 minutes before eating.


Insulin glulisine, is the third rapid acting formulation.  Like the other two it has amino acid substitutions that allow for a more rapid absorption. Glulisine has an onset of action= 0.25 hours, with a peak of 30-90 minutes and a duration of 2-4 hours

Apidra® U-100 (glulisine) was approved in July 2004.  Apidra is available as vials and Solostar pens.

Lots has been in the news about the ridiculous insulin prices in the United States.  Your Thompson Pharmacist is a great resource to help you understanding your fast-acting insulin, and getting you the most value for your money.  Count on your Thompson Pharmacist for all of your diabetic supplies.  At Thompson Pharmacy it’s all for you!!