A short-acting, soluble, non-suspended insulin produced from r-DNA/GE/GM, bovine, or porcine sources. R or neutral insulin is basically zinc insulin crystals dissolved in clear fluid with nothing added to alter its action or speed.  From 1921 to the 1930's when PZI was developed, R was the only kind of insulin available. 
While both R/neutral and semilente insulins are considered fast-acting, they differ in a few ways. As above, there's no suspension or buffer  in R/neutral; it's totally dissolved and soluble, meaning it can safely be used intravenously.  R/neutral is clear and does not need to be resuspended before using.
The very small insulin particles in semilente insulin are suspended by zinc. . Semilente is cloudy, has an acetate buffer and cannot be used intravenously. Semilente also needs resuspending before being used.
|All Short acting|
|Hypurin Bovine Neutral|
Betasint Bovine Corriente
|Iletin R (No longer produced.)|
Hypurin Vet Neutral (No longer produced.)
Insuvet Neutral (No longer produced.)
|Iletin I R (No longer produced.)|
|Betasint Porcine Corriente|
Hypurin Porcine Neutral
Hypurin Pork Regular
|Pork Actrapid (No longer produced.)|
Iletin II R (No longer produced.)
|Actrapid, Huminsulin Normal|
Humulin C, Humulin R
Humulin Regular, Humulina Regular
Humuline R, Humuline Regular
Humulin S, Insuman Rapid
Novolin R, Umuline Rapide
Umuline Regular, Winthrop Rapid
Humulin ReliOn R
|R-DNA||ReliOn/Novolin R (No longer produced.)|
- ↑ Definition of Neutral Insulin-Should Say "Mammalian". InChem.
- ↑ Humulin R. Eli Lilly.
- ↑ Chase, Lillian A. (1938). Some Rules for Dosage of Protamine Zinc Insulin. Canadian Medical Journal.
- ↑ 4.0 4.1 4.2 DeRuiter, Jack. Insulin Preparations-Regular Insulin. Auburn University.
- ↑ Maddison, Jill E.,Page, Stephen W.,Church, David B. (2008). Small Animal Clinical Pharmacology. Saunders Ltd..
- ↑ Deckert, T. (1980). Intermediate-Acting Insulin Preparations: NPH (Isophane) & Lente. Diabetes Care.
Note--in 1980, there was only beef Lente-type insulin--no pork or r-DNA/GE/GMLente insulins
- ↑ Resource Guide. American Diabetes Association (2005).
- Absorption Kinetics of Regular (Neutral) & Isophane (NPH) Insulin in the Normal Dog Goeders LA, Esposito LA, Peterson ME., 1987, Domestic Animal Endocrinology
- NACDS-Insulin Chart-Page 2
- Insulin therapy for dogs and cats Dowling, Patricia, 1995, Canadian Veterinary Journal