Humalog Classification
Humalog (insulin lispro) is a rapid-acting insulin analog used for prandial (mealtime) glucose control in diabetes mellitus. 1
Pharmacologic Category
Humalog is a biosynthetic human insulin analog created by reversing the positions of proline and lysine amino acids at positions B-28 and B-29 in the C-terminal portion of the B chain of human insulin. 1, 2 This minor structural modification prevents the insulin molecules from self-associating into hexamers, allowing for much faster absorption after subcutaneous injection compared to regular human insulin. 2
Pharmacokinetic Profile
The rapid-acting characteristics that define Humalog include:
- Onset of action: Within 5-15 minutes after subcutaneous injection 3
- Peak effect: 1-3 hours after administration 3
- Duration of action: 3-5 hours 3
These pharmacokinetics are substantially faster than regular human insulin, with insulin lispro achieving peak serum concentrations that are three times higher and reaching peak 4.2 times faster than regular insulin. 4 The absorption rate constant is double that of regular insulin, while the duration of action is half as long. 4
Clinical Role and Indications
Humalog functions as prandial insulin - meaning it is specifically designed to control postprandial (after-meal) blood glucose excursions. 5 The American Diabetes Association recommends administering rapid-acting insulin analogs like Humalog 15 minutes or less before meals for optimal postprandial glucose control. 3
Dosing Framework
For initiating mealtime insulin therapy:
- Starting dose: 4 units per meal, 0.1 units/kg per meal, or 10% of the basal insulin dose per meal 5
- Can be administered immediately before or even after meals due to its rapid onset 1, 6
Comparison to Other Insulin Types
Unlike basal insulins (such as NPH, glargine, or degludec) which provide background insulin coverage throughout the day, Humalog is classified alongside other rapid-acting analogs as a bolus or prandial insulin. 5 The time-action profile of insulin lispro mimics the physiological response of endogenous human insulin to food intake. 1
Available Formulations
Humalog is available both as:
- Monotherapy (Humalog alone) for flexible prandial dosing 1
- Premixed formulations (Humalog Mix25 or Mix50) containing both rapid-acting lispro and longer-acting neutral protamine lispro 1
- Concentrated formulation U-200 (200 units/mL) for patients requiring large insulin doses 5
Clinical Advantages
The rapid-acting nature provides better matching of peak insulin action to food absorption, improved glycemic control in the immediate postprandial period, and reduced risk of hypoglycemia between meals compared to regular human insulin. 2, 6 This allows greater lifestyle flexibility since patients do not need to inject 30 minutes before meals as required with regular insulin. 2, 6