Insulin lispro
lispro, LY275585, Lys(B28), Pro(B29) human insulin, insulin lispro-aabc, ultra-rapid lispro
Insulin lispro was the first engineered insulin analogue ever licensed, approved in 1996. It is human insulin with two adjacent B-chain residues swapped, a change that weakens the molecule's tendency to self-associate and lets it be absorbed from the injection site within minutes rather than tens of minutes. It is used to cover meals and to correct high glucose, and it is the standard insulin in most insulin pumps.
Mechanism
Insulin lispro is a positional isomer of human insulin: proline at B28 and lysine at B29 are transposed to give lysine at B28 and proline at B29. Nothing is added or removed, so the molecular formula and mass are identical to human insulin. The functional consequence is entirely about self-assembly. In the formulation vial, insulin exists as zinc-coordinated hexamers stabilised by phenolic preservative. The B28 proline of human insulin sits at the monomer-monomer interface and makes hydrophobic contacts essential to dimer formation; reversing the ProB28-LysB29 pair (a trick borrowed from the corresponding region of insulin-like growth factor I, which does not dimerise) places a charged lysine at that interface and introduces steric and electrostatic repulsion.
The hexamer therefore still forms in the vial, giving the product adequate shelf stability, but dissociates far more readily once injected and diluted in subcutaneous fluid. Because only monomers and dimers cross the capillary endothelium efficiently, faster hexamer breakdown translates directly into faster absorption: appearance in plasma within about 15 minutes, a peak at 30 to 90 minutes, and a duration of three to five hours, against roughly 30 minutes, two to four hours and six to eight hours for soluble human insulin. Receptor pharmacology is essentially unchanged. Insulin receptor affinity and IGF-1 receptor affinity are close to those of human insulin, and downstream signalling through IRS/PI3K/AKT with GLUT4 translocation and suppression of hepatic glucose output is identical. An ultra-rapid formulation adds treprostinil, which causes local vasodilatation, and citrate, which increases local vascular permeability, further accelerating absorption without altering the peptide itself.
What the research shows
Lispro's registration evidence is unambiguous on pharmacokinetics and postprandial glucose: absorption is roughly twice as fast as soluble human insulin, postprandial excursions are cut by one to two millimoles per litre, and the drug can be taken immediately before eating rather than half an hour beforehand, a practical advantage that patients consistently rate highly. The 1,008-participant Anderson trial also showed about a 12% reduction in hypoglycaemia, most pronounced overnight, which follows logically from the shorter tail of action.
Where the evidence is weaker than commonly assumed is in HbA1c and hard outcomes. The Cochrane review by Fullerton and colleagues, which pooled the randomised evidence in adult type 1 diabetes, found only a minor benefit (HbA1c differences of around 0.15 percentage points, at the edge of clinical relevance) and rated the certainty of evidence as low. No randomised trial has followed patients long enough to show that rapid-acting analogues reduce retinopathy, nephropathy, neuropathy, cardiovascular events or mortality relative to regular human insulin; the complication reductions attributed to intensive therapy come from the DCCT, which used regular human insulin and isophane insulin, not analogues. The honest summary is that lispro is a genuine engineering success that made flexible mealtime dosing practicable, that its clinical superiority over regular human insulin is modest, and that its main real-world contributions have been to pump therapy and to convenience. In insulin pumps its advantage is clearer, because the rapid off-rate is what makes closed-loop and hybrid closed-loop algorithms feasible at all.
Evidence assessment
High-quality evidence
Approved by the FDA in 1996 and in the European Union in the same year, on the basis of large multicentre randomised trials including a 1,008-participant crossover study, and supported by a Cochrane systematic review. The evidence robustly establishes the pharmacokinetic advantage and improved postprandial glucose; Cochrane's assessment is that the resulting clinical benefit over regular human insulin is minor, and that data on long-term complications are absent.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Reduction of postprandial hyperglycemia and frequency of hypoglycemia in IDDM patients on insulin-analog treatment Preclinical only
Lispro injected immediately before meals reduced the postprandial glucose rise compared with regular human insulin given 30 to 45 minutes before meals, by roughly 1.3 mmol/L at one hour and 2.0 mmol/L at two hours. Hypoglycaemic episodes were about 12% less frequent, with the largest relative improvement overnight. The HbA1c difference was small.
Insulin lispro in CSII: results of a double-blind crossover study Preclinical only
Lispro produced higher and earlier peak insulin concentrations with a shorter duration after subcutaneous delivery, translating into lower postprandial glucose and lower HbA1c in pump therapy. This trial is a major reason lispro became the default pump insulin.
Short-acting insulin analogues versus regular human insulin for adults with type 1 diabetes mellitus Preclinical only
The reviewers concluded there is only a minor benefit of short-acting insulin analogues over regular human insulin, with mean HbA1c differences of the order of 0.15 percentage points and low-certainty evidence on hypoglycaemia. No trial provided data on long-term complications, mortality or health-related quality of life. This is the most important sceptical counterweight to the registration trials.
Efficacy and Safety of Rapid-Acting Insulin Analogs in Special Populations with Type 1 Diabetes or Gestational Diabetes: Systematic Review and Meta-Analysis Preclinical only
Rapid-acting analogues including lispro were at least as effective and safe as regular human insulin in pregnancy, in children and adolescents, and in continuous subcutaneous infusion, with modest advantages in postprandial glucose. Effect sizes in these special populations were small and the evidence base thinner than in general adult type 1 diabetes.
Safety
Hypoglycaemia is the principal risk and the effect that limits dosing; with a rapid-acting analogue it appears sooner after injection than with regular human insulin, so mistimed dosing relative to a meal is a common precipitant. Because lispro has a short duration and there is no subcutaneous depot, insulin pump failure or set occlusion can lead to diabetic ketoacidosis within hours, considerably faster than with older regimens. Weight gain, hypokalaemia, injection-site lipohypertrophy from inadequate site rotation, and injection-site reactions all occur. Rare adverse effects include systemic insulin allergy, lipoatrophy, peripheral oedema, transient refractive change on rapid glycaemic improvement, and clinically significant anti-insulin antibodies. Renal or hepatic impairment reduces insulin clearance and increases hypoglycaemia risk. Concurrent thiazolidinedione therapy increases fluid retention and heart-failure risk. Recurrent hypoglycaemia causes hypoglycaemia unawareness, with specific implications for driving; UK drivers treated with insulin must comply with DVLA requirements. Insulin is a high-alert medicine and the availability of 100 and 200 units/mL lispro products is a recognised source of tenfold error. Non-medical use, including use by bodybuilders for putative anabolic effect, has caused deaths and permanent hypoglycaemic brain injury. There is no safe recreational or performance use of any insulin, and rapid-acting analogues are the most dangerous in this respect because the onset leaves little time to intervene.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Licensed by the MHRA for the treatment of adults and children with diabetes requiring insulin for maintenance of normal glucose homeostasis, and for initial stabilisation of diabetes. Prescription-only medicine (POM). Recommended within NICE guidance NG17 for type 1 diabetes, and on the WHO Model List of Essential Medicines as a rapid-acting insulin. |
| United States | FDA-approved in June 1996 (the first recombinant insulin analogue ever licensed) for type 1 and type 2 diabetes in adults and children. An ultra-rapid formulation containing treprostinil and citrate was approved in June 2020. Since March 2020 insulin lispro has been regulated as a biological product, and follow-on and biosimilar products are available. Prescription-only. |
| WADA (sport) | Prohibited at all times, in and out of competition, under section S4 of the WADA Prohibited List (Hormone and Metabolic Modulators), which covers insulins and insulin-mimetics. Athletes with diabetes require a Therapeutic Use Exemption. |
Questions
Nothing about receptor binding: the two are functionally equivalent at the insulin receptor. The difference is self-assembly. Regular human insulin sits in the vial as zinc hexamers that must dissociate to dimers and then monomers before they can cross the capillary wall, and that dissociation is slow. Swapping proline B28 and lysine B29 puts a charged residue at the dimer interface, so the hexamer falls apart much faster once injected and diluted.
It is faster and more convenient, and it lowers post-meal glucose peaks by one to two millimoles per litre. Whether that amounts to a clinically important benefit is contested: the Cochrane review found only a minor advantage in HbA1c and low-certainty evidence on hypoglycaemia, and no trial has shown that lispro reduces long-term diabetes complications relative to regular human insulin. Its clearest advantage is in insulin pump therapy.
Pumps deliver only rapid-acting insulin, and the algorithms controlling modern hybrid closed-loop systems depend on the insulin acting and clearing predictably within a few hours. Lispro's rapid on and off kinetics make that control loop tractable. The corollary is that if pump delivery is interrupted, there is no depot of long-acting insulin, and ketoacidosis can develop within a few hours.
Yes. Lispro is a positional isomer (two adjacent residues are swapped, not changed), so both have the formula C257H383N65O77S6 and a mass of about 5808 daltons. This is unusual among engineered analogues; aspart, glulisine, glargine, detemir and degludec all differ from human insulin in composition, not just in sequence order.
It is the same lispro peptide in a modified formulation containing treprostinil, a prostacyclin analogue that dilates local blood vessels, and citrate, which increases local vascular permeability. Both accelerate absorption from the injection site, bringing onset forward by roughly 10 to 15 minutes. The insulin molecule itself is unchanged.