Diabetes in Pets
Humulin N
NPH/Isophane by Eli Lilly
intermediate-acting r-DNA/GE/GM
U100 Isophane
Line Humulin
Also known as Humulin I
Similar to  
Action in cats  
  • onset 1-2h,
  • sharp peak 4-6h,
  • duration 8-12h[1][2]
Action in dogs  
  • onset 0.5-3h,
  • peak 2-10h[3],
  • duration 4-24h
Use and Handling
Type cloudy
Shelf Life 24 months
When opened 28 days room temp.
In pen 28 days room temp.

Humulin N is Eli Lilly's brand name for their NPH-based insulin product[4].

It is an intermediate-acting insulin, though in cats this tends to be closer to short-acting in practise.

Like all other isophane/protamine suspended insulins[5], it is a crystalline suspension with protamine.

NPH (Isophane) insulin was originally developed by Novo Nordisk labs in 1946, as an insulin with intermediate action. The versions currently sold are identical to human insulin and therefore differ slightly from feline and canine insulin.

Technical details[]

This type of insulin tends to have an onset of 2-4 hours, a peak action of 4-10 hours, and a total duration of 10-20 hours, in humans.

These times seem to be similar in dogs, but considerably compressed in cats, possibly because of cats' faster metabolism.

Cats seem instead to experience a 1-2 hour onset, a peak action of 4-6 hours, and a total duration of 8-12 hours maximum, according to user surveys on Felinediabetes.com

Humulin N or generic NPH, and their Novo Nordisk competitor Novolin N aka Insulatard[6][7][8]and aka Protaphane[9], are available in the USA without a valid prescription.

In the UK, Humulin N is known as Humulin I ("I" standing for its isophane suspension.)[10][11][12]. Aventis also makes a similar NPH insulin called Insuman Basal[13][14].

Further Reading[]