What are the differences among Fiasp (faster‑acting insulin aspart), Humalog (insulin lispro), and Lyumjev (insulin lispro‑aik) rapid‑acting insulin analogues?

Differences Among Fiasp, Humalog, and Lyumjev

Lyumjev (ultra-rapid lispro) is the fastest-acting insulin, providing superior postprandial glucose control compared to standard Humalog, while Fiasp (faster-acting aspart) shows no clinically meaningful advantage over standard rapid-acting insulins like Humalog. 1

Key Pharmacokinetic Distinctions

Lyumjev (Ultra-Rapid Lispro)

• Lyumjev demonstrates the most accelerated insulin absorption profile, with early 50% time to maximum concentration reduced by 6-12 minutes compared to standard Humalog, and area under the curve in the first 15 minutes increased 2.5- to 4.3-fold. 2
• Lyumjev provides significantly faster recovery from hyperglycemia, reducing time to glucose normalization by 16-23 minutes compared to Humalog in real-world scenarios including missed meal boluses and basal insulin suspension. 2
• Postprandial glucose control is markedly superior with Lyumjev: it reduces 2-hour and 4-hour incremental area under the curve by 92-151 mmol/L following breakfast and evening meals, with 4-hour time in target range increased by 5.7-6.7 percentage points compared to standard lispro. 1

Fiasp (Faster-Acting Aspart)

• Fiasp shows no significant clinical advantage over standard insulin aspart in hybrid closed-loop systems, with no differences in 2-hour or 4-hour postprandial glucose excursions, time in target range, or time above range during any meal. 1
• Despite being marketed as "faster-acting," Fiasp failed to demonstrate meaningful improvements in postprandial glucose control in head-to-head comparisons. 1

Humalog (Standard Insulin Lispro)

• Humalog and standard insulin aspart (Novolog) have nearly identical action profiles: onset 0.25-0.5 hours, peak 1-3 hours, duration 3-5 hours. 3
• These insulins are NOT interchangeable products and require a prescription change to switch between them, despite their similar profiles. 3

Clinical Implications for Practice

When to Choose Lyumjev

• Lyumjev is the preferred choice for patients struggling with postprandial hyperglycemia, particularly after breakfast and evening meals where it demonstrates the most pronounced benefits. 1
• Consider Lyumjev for patients using continuous subcutaneous insulin infusion (pump therapy) who experience frequent hyperglycemic excursions requiring correction boluses. 2
• Lyumjev offers particular advantage in hybrid closed-loop systems where faster insulin action translates to measurably better glucose control. 1

When Fiasp Offers No Advantage

• Do not expect clinical benefit from switching standard insulin aspart to Fiasp, as controlled trials demonstrate no improvement in postprandial control or time in range. 1
• The additional cost of Fiasp is not justified by clinical outcomes in most patients. 1

Standard Rapid-Acting Analogues Remain Appropriate

• The American Diabetes Association recommends rapid-acting insulin analogues (lispro, aspart, or glulisine) as prandial insulin in basal-bolus regimens and continuous subcutaneous insulin infusion for both type 1 and type 2 diabetes. 4, 3
• These standard formulations reduce HbA1c by an additional 0.15% compared to regular human insulin and significantly reduce hypoglycemia risk compared to human insulins. 5

Common Pitfalls to Avoid

• Do not assume "faster-acting" marketing claims translate to clinical superiority: Fiasp's label as faster-acting aspart did not produce measurable benefits in rigorous trials. 1
• Do not mix or interchange these products without a new prescription: despite similar mechanisms, they are distinct pharmaceutical products requiring formal prescription changes. 3
• Cost considerations matter—insulin aspart and lispro costs may differ substantially, affecting patient access and adherence. 3