Short answer: Both are mealtime insulins injected at the start of a meal or within 20 minutes after starting, for adults and children with diabetes.12 Fiasp is insulin aspart with niacinamide; Lyumjev is insulin lispro-aabc with treprostinil and sodium citrate. Fiasp is U-100 only; Lyumjev also comes as U-200. Fiasp was tested against NovoLog and Lyumjev against Humalog, never against each other.
| Fiasp | Lyumjev | |
|---|---|---|
| Insulin | Insulin aspart; inactive ingredients include niacinamide and arginine1 | Insulin lispro-aabc; inactive ingredients include treprostinil and sodium citrate2 |
| When injected | At the start of a meal or within 20 minutes after starting1 | At the start of a meal or within 20 minutes after starting2 |
| Strengths and forms | U-100: vial, FlexTouch pen, PenFill and PumpCart cartridges1 | U-100: vial, KwikPen, Junior KwikPen, Tempo Pen, cartridge. U-200: KwikPen2 |
| How fast (label studies) | In the blood about 2.5 minutes after a dose; peak at about 63 minutes1 | In the blood about 1 minute after a dose; peak at 57 minutes2 |
| Insulin pump | Reservoir at least every 6 days; PumpCart every 4 days1 | U-100 only; reservoir at least every 9 days2 |
| Pump site reactions | Infusion site reactions in 10.2% of adults1 | Infusion site reactions in 37.7% of adults; 3.3% stopped2 |
| Severe lows, type 1 adults | 6.7% mealtime, 8.0% after the meal1 | 5.5% mealtime, 4.6% after the meal2 |
| Comparator in label trials | NovoLog1 | Humalog2 |
| Missed dose | Check blood sugar to decide if a dose is needed; resume at the next meal1 | Check glucose to decide if a dose is needed; resume at the next meal2 |
Not in either label. Fiasp's trials compared it with NovoLog and met a 0.4% HbA1c non-inferiority margin; Lyumjev's PRONTO trials compared it with Humalog and met the same margin.12 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Average weight gain in type 1 adults was 0.7 kg on Fiasp and 0.6 kg on Lyumjev, and in type 2 adults 2.7 kg and 1.5 kg, again from separate trials.12
Yes. Both list low blood sugar as the most common reaction, plus never sharing pens, insulin changes under supervision, mix-ups, low potassium, allergic reactions, heart failure with thiazolidinediones and pump failure. Neither has a boxed warning. Lyumjev U-200 is never drawn into a syringe, used in a pump or given into a vein.12
Which, if either, fits is for your prescriber. More detail: Fiasp side effects, Lyumjev side effects, the Fiasp and Lyumjev dosing schedules, the Fiasp and Lyumjev missed-dose pages, Fiasp vs NovoLog: what is different about the faster insulin aspart? and Lyumjev vs Humalog: what changes with the newer insulin lispro?.