Diabetes in Pets
Iletin I Lente
Lente by Eli Lilly
intermediate-acting Bovine
U100 Zinc
Line Iletin
Also known as beef lente
Similar to  
Action in cats  
  • onset 2-5h[1],
  • peak 12-24h
  • duration: maximum 36h
Action in dogs  
  • onset 2-5h,
  • peak 12-24h,
  • duration: maximum 36h
Use and Handling
Type cloudy
Shelf Life 24 months
When opened 28 days
In pen N/A

Eli Lilly's old product[2]--a 100% bovine lente insulin which is intermediate-acting.

Current equivalents are: Hypurin Bovine Lente[3][4][5] by CP Pharma and Insuvet Lente by Schering-Plough Animal Health[6].

It shared the Lente composition[7] definition of being a suspension of crystalline (ultralente) and amorphous (semilente) insulin in a ratio of 7 crystalline parts to 3 amorphous parts.

What Lente Is Not

No Lente-type insulin regardless of species can contain any NPH/isophane insulin[8] or any R/Neutral insulin[9].

Both are chemically impossible: the phenol preservative present in NPH/isophane alters the action of Lente-type insulins, creating a mixture with an approximate action of R/Neutral[10].

The zinc suspension of Lente-type insulin binds R/Neutral, causing the short-acting insulin to slow, losing its short-acting effect[11][12].

Combining Lente Family Insulins

Insulin manufacturers[13] indicate that R/neutral and semilente, Lente, ultralente insulins are able to be combined in the same syringe, but only just before injection. In pre-filled syringes, the zinc suspension of the Lente-type insulins binds the R/neutral, causing it to lose its short-acting effect. Various studies have documented this, and some doctors advise against using R/neutral in the same syringe with the Lente family of insulins[14][15][16][17].

None of the Lente family of insulins (semilente, Lente, Ultralente) can be combined with[18] NPH/isophane insulins. The phenol preservatives present in NPH-type insulins alters the Lente-types to the point where they become a close approximation of R/neutral, with regard to action[19].

Keeping the phenol preservatives in mind, all protamine-suspended insulin mixes would be "off limits" regarding same syringe mixing with any Lente-type insulins[20].

Feline insulin compared with Bovine, Human, & Porcine versions. Up to 4 amino acids differ. The closest match is bovine with only one amino acid difference; the least close is human with four amino acid differences.

Lilly also produced an 85% bovine, 15% porcine insulin under the same Iletin I trade name in the same various types. The blended beef/pork Iletin I was produced until ca. 2002.


  1. Petsulin Lente Note Re: shorter feline duration
  2. Discontinuation of Lilly's Iletin I beef/pork line of insulins; Iletin I Lente is at right.
  3. Hypurin Bovine Lente Patient Information
  4. Electronic Medicines Compendium (EMC) UK-Hypurin Bovine Lente
  5. Hypurin Bovine Lente--Lente Beef Insulin Remedyfind.com
  6. Prescribing Bovine Insulin
  7. EMEA Scientific Discussion-Monotard
  8. Combining Lente-type Insulins with Phenol-Preserved Insulins
  9. Lente Zinc Suspension Causes Loss Of R/Neutral Short-Acting Effect
  10. Lente-Type Insulins & NPH/Isophane Insulins-A Bad Combination
  11. Intermediate-Acting Insulin Preparations: NPH (Isophane) & Lente Diabetes Care-1980
    Note--in 1980, there was only beef Lente-type insulin--no pork or r-DNA/GE/GMLente insulins
  12. Resource Guide 2005-American Diabetes Association
  13. Insulin Producers vs Doctors Re:Combining R/Neutral & Lente-type Insulins
  14. Availability of Soluble (R/Neutral) Insulin in Mixed Preparations of Crystalline (Lente) & Ultralente GE Insulins-Clinical Therapeutics-1991
  15. Absorption Kinetics & Action Profiles-Single Subcutaneous Administration of Human Soluble (R/Neutral) & Lente Insulin-Diabetes Care-1987
  16. Delayed Onset of Action of Soluble (R/Neutral) Insulin After Premixing With Lente Insulin Diabetes Research & Clinical Practice-1983
  17. RxEd.org-Insulin Therapy-Mixing Precautions
  18. Phenol Preservatives & Lente-type Insulins--A Bad Combination
  19. RxEd.org-Insulin Therapy-Mixing Precautions
  20. RxEd.org-Insulin Therapy-Mixing Precautions