Corticosteroids stimulate glucose secretion by the liver as well as reduce glucose transport into fat and muscle cells. The overall effect is a reduction in glucose clearance. Elevated glucose levels can lead to glucose toxicity further impairing insulin secretion. Prednisone can also impair GLUT-2 expression. GlUT-2 is a protein mediated glucose transporter that ferries glucose across cell membranes. That means that people with diabetes taking prednisone are likely to see a significant bump in their blood glucose numbers depending on the dose of steroid given.
One of the most difficult things about taking prednisone is that it doesn’t elevate glucose readings consistently throughout the day. Prednisone taken in the morning usually doesn’t cause glucose levels to start to rise until lunch time. Blood glucose readings usually stay high through the early evening hours and then decline over night. Many people have normal or low glucose readings in the morning while taking prednisone.
This type of action curve can make it difficult to use flat basal insulin such as Lantus® or Levemir® to treat people taking prednisone. Sometimes the use of NPH can be helpful for people on prednisone as it has a peak mid-afternoon, and if given in the morning its effects taper off toward the evening, mirroring the action of the prednisone.
When using NPH, the overall effect is a better balance between your glucose levels and your insulin throughout the day.