Insulin lispro (Humalog)

Insulin lispro was the first rapid-acting insulin analog, approved by the US FDA in 1996 and in the European Union the same year.¹⁶ It is a mealtime (bolus) insulin: you take it just before eating to cover the glucose rise from food, alongside a separate long-acting basal insulin. Its arrival is a landmark — it was the molecule that made fast, flexible bolus dosing possible and set the template every later rapid analog was measured against.²

How it works. Lispro is human insulin with two amino acids on the B-chain swapped — the proline at B28 and lysine at B29 are reversed.¹ That small change means it is absorbed faster than older "regular" human insulin after a subcutaneous injection.¹ In head-to-head studies versus regular human insulin summarized in a 1996 review, lispro reached a peak blood level about three times higher, roughly four times faster, with about half the duration.³

The real numbers (PK/PD). Injected under the skin, lispro peaks about 30–90 minutes after dosing and has a more rapid onset and a shorter duration of action than regular human insulin.¹ The label therefore advises dosing within 15 minutes before a meal (or immediately after).¹ Like all injected insulins it is not perfectly reproducible: absorption typically varies on the order of 15–25% within the same person from day to day and site to site — a variability broadly similar across rapid analogs.⁴

Around exercise. The multi-hour tail is the main thing to plan around: a mealtime dose taken before activity can still be active during it, and in a study of children and adolescents with type 1 diabetes, late (post-exercise) hypoglycemia was more common than lows during the exercise itself.⁵ Pump users and people on injections usually reduce insulin and/or add carbohydrate around planned activity.

Delivery and approvals. Lispro is delivered by syringe, prefilled pen (KwikPen), or insulin pump — it is FDA-approved for continuous subcutaneous infusion in pumps.¹ It is indicated for adults and children with diabetes and is on the WHO Model List of Essential Medicines.

Access, cost, and biosimilars. Lispro is one of the most widely available insulins in the world. Beyond branded Humalog, there is a Lilly authorized generic ("Insulin Lispro"), launched in 2019 at a substantially lower list price than Humalog, and a follow-on/biosimilar from Sanofi, Admelog (FDA-approved December 2017).⁹ Under price pressure, in March 2023 Lilly sharply cut the list price of Humalog and made its non-branded lispro markedly cheaper, alongside a much lower monthly out-of-pocket cap for many patients.⁹ Real-world access still varies by country and insurance, but on price and availability lispro now scores well.

What's coming. The clearest next step is faster. Lilly's ultra-rapid lispro (Lyumjev / insulin lispro-aabc) — a reformulation of the same molecule with absorption-accelerating excipients — was FDA-approved in June 2020.⁸ In controlled studies it reaches an early half-maximal level about 13 minutes sooner than Humalog and cuts the post-meal glucose rise, more closely matching a healthy mealtime response.⁷ For the artificial-pancreas goal, this push toward a truly meal-speed insulin is exactly the gap that needs closing — and lispro's own faster successor is the leading edge of it.²