NPH Insulins, or "Neutral Protamine Hagedorn", now describes the set of insulins using Isophane / Protamine as their suspension. In North America, Humulin N and Novolin N are the most common brands of NPH insulin. Another term for this type of insulin is Isophane; it's commonly used to describe this insulin type outside of North America.
The difference between NPH/isophane insulin and PZI insulin is the amount of protamine in the suspension. PZI has more of it and this is what makes it a slow-acting insulin, in contrast to NPH/isophane being an intermediate-acting one for both dogs and people,  as the additional protamine extends the duration.
Specifications of NPH/isophane insulinEditBritish National Formulary  defines this type as: A sterile suspension bovine or porcine or of human insulin in the form of a complex obtained by the addition of protamine sulphate or another suitable protamine.
British Pharmacoepia and United States Pharmacopia definitions: 
Sterile buffered suspension of insulin in the form of a complex obtained by addition of suitable protamine. Prepared from crystalline insulin. pH 6.9 - 7.5 iso-osmotic with blood. Contains for each 100 units of insulin, 300 - 600 g protamine sulphate and not more than 40 g zinc, a suitable bactericide and sodium phosphate as buffering agent.
USP specification: Sterile suspension of zinc insulin crystalline and protamine sulphate in buffered water for injection. Solid phase contain crystals of insulin
protamine and zinc; 40, 80, 100 units/ml. Contains glycerol, metacresol, phenol sodium phosphate and zinc.
Additional detailsEditNPH is widely used for treatment of diabetic dogs.  With a peak of 1.5-6 hours and duration of 4-10 hours, if it is successfully used, twice-daily dosing is a must. 
This 1987 study  of direct comparisons between R and NPH insulins in dogs, found R insulin to be absorbed better than NPH and suggests that NPH insulin may have an earlier peak and shorter duration than previously thought.
The following commercial insulins are all generically NPH insulins:
|All Intermediate acting|
|Betasint Bovine NPH|
Hypurin Bovine Isophane 
(No longer produced.)
|Iletin I NPH
(No longer produced.)
|Betasint Porcine NPH|
Hypurin Porcine Isophane 
Hypurin Pork NPH
|Iletin II NPH (No longer produced.)|
Pork Insulatard 
(No longer produced.)
Leo Retard (No longer produced.)
|Huminsulin Basal, Humulin I|
Humulin N, Humulin NPH
Humulina NPH, Humuline N
Humuline NPH, Umuline NPH
Humulin ReliOn N
|Insuhuman Basal, Insuman Basal|
Isuhuman Basal, Winthrop Basal
|Insulatard, Novolin N|
(No longer produced)
Other commonly used names are:
- NPH insulin, NPH
- isophane insulin
- ↑ Gordon, Jana (April 2008). Insulin therapy: Past, present and future. DVM 360.
- ↑ Nelson, Richard (2006). Selecting an Insulin for Treatment of Diabetes Mellitus in Dogs & Cats-page 41. OSU Endocrinology Symposium.
- ↑ 3.0 3.1 British National Formulary-Isophane/NPH Insulin Definition. InChem.
- ↑ Insulin Choice for Dogs. BD Diabetes.
- ↑ Ask the D Team-Some People Find it Inconsistent Also. Children With Diabetes (2000).
- ↑ Davidson, Gigi. Providing care for veterinary diabetics-page 3. International Journal of Pharmaceutical Compounding.
- ↑ Goeders LA, Esposito LA, Peterson ME. (1987). Absorption Kinetics of Regular (R)/(Neutral) & Isophane (NPH) Insulin in the Normal Dog. Domestic Animal Endocrinology.
- ↑ Hypurin Bovine Isophane Patient Information. Net Doctor.co.uk.
- ↑ Hypurin Bovine Isophane. Wockhardt UK.
- ↑ Prescribing Bovine Insulin.
- ↑ 11.0 11.1 Response to Withdrawal of Novo Porcine Insulins. CP/Wockhardt UK.
- ↑ Prescribing Porcine Insulin.
- ↑ Prescribing Novo Animal Insulin.
- ↑ Patient Information Leaflet-Pork Insulatard. Novo Nordisk.
- Absorption Kinetics of Regular (Neutral) & Isophane (NPH) Insulin in the Normal Dog Goeders LA, Esposito LA, Peterson ME., 1987, Domestic Animal Endocrinology
- The Use of Isophane (NPH) Insulin for the Control of Diabetes Mellitus in Dogs Lorenzen FH., 1992, Acta Vetinaria Scandinavica
- Dosing information on NPH use for dogs Rand, Jacqueline, Fleeman, Linda, University of Queensland
- InChem--with information on NPH/isophane insulins.
- An investigation of the action of Neutral Protamine Hagedorn human insulin in dogs with naturally occurring diabetes mellitus Palm, C. A., et. al, 2009, Journal of Veterinary Internal Medicine
- NACDS-Insulin Chart-Page 2
- Treatment of Diabetes Mellitus in Dogs Using Isophane Insulin Penfills Thoresen SI, Lorenzen FH., 1998, Acta Veterinaria Scandanavica
- Insulin therapy for dogs and cats Dowling, Patricia, September 1995, Canadian Veterinary Journal