Also known as: Humulin R · Novolin R · regular human insulin · short-acting insulin
Regular human insulin (Humulin R, Novolin R) is a short-acting insulin with an elimination half-life of approximately 2 hours following subcutaneous injection[1], based on FDA-approved prescribing information. Onset of glucose-lowering action occurs at 30–60 minutes, peak effect at 2–4 hours, and duration of approximately 5–8 hours. Regular insulin is identical in amino acid sequence to endogenous human insulin and is produced by recombinant DNA technology.
| Parameter | Value (SC) | Source |
|---|---|---|
| Elimination Half-Life | ~2 hours | FDA Humulin R Prescribing Information[1] |
| Onset of Action | 30–60 minutes | FDA Humulin R label[1] |
| Time to Peak Effect (Tmax) | 2–4 hours | FDA Humulin R label[1] |
| Duration of Action | 5–8 hours | FDA Humulin R label[1] |
| Bioavailability (SC) | ~55–77% | FDA label; varies by injection site |
| Full Clearance (5 × t½) | ~10 hours | Calculated from label PK data |
| IV Half-Life | ~5–15 minutes | FDA Humulin R label (IV use)[1] |
| Primary Clearance Route | Receptor-mediated degradation; liver (~60% first-pass), kidney | FDA Humulin R label[1] |
| Pre-meal Injection Timing | 30–45 minutes before meals | FDA-approved labeling |
| Data Quality | Human RCT — FDA-approved prescribing information (Humulin R, Novolin R) | |
Regular human insulin has an elimination half-life of approximately 2 hours following subcutaneous injection, per FDA-approved prescribing information for Humulin R.[1] This places it between rapid-acting insulin analogues (~1 hour SC) and intermediate-acting NPH insulin (~4–6 hours SC), earning it the classification "short-acting" rather than "rapid-acting."
The 2-hour half-life reflects the slow dissociation of insulin hexamers at the subcutaneous injection depot — native human insulin strongly self-associates into hexamers at the concentrations found in vials and pens, and these hexamers must dissociate into dimers and then monomers before absorption into capillaries can occur. This rate-limiting step is the pharmacokinetic basis for regular insulin's longer onset vs rapid-acting analogues.
Pharmacokinetic parameters for regular insulin are derived from euglycaemic clamp studies in which blood glucose is clamped at a fixed concentration while exogenous insulin is infused and glucose infusion rate quantifies insulin action. Serial plasma insulin sampling provides t½, Tmax, and AUC values reported in FDA-approved labeling.
Regular insulin's plasma half-life (~2 hours SC) does not equal its biological effect duration (~5–8 hours). Glucose-lowering action extends well beyond plasma peak because downstream GLUT4 translocation, glycogen synthesis stimulation, and hepatic glucose production suppression continue after the hormone begins clearing. The extended 5–8 hour action tail is clinically important: late hypoglycaemia is a known risk with regular insulin if carbohydrate intake is not sustained through the full duration of action.
| Half-Lives Elapsed | Time After SC Injection | % Remaining in Plasma | Clinical Note |
|---|---|---|---|
| 1 | ~2 hours | 50% | Still in absorption phase; approaching peak effect |
| 2 | ~4 hours | 25% | At or past peak glucose-lowering; significant action remains |
| 3 | ~6 hours | 12.5% | Late action tail; hypoglycaemia risk without carbohydrate |
| 4 | ~8 hours | 6.25% | Action largely resolved for most individuals |
| 5 (threshold) | ~10 hours | ~3% | Pharmacologically negligible in plasma |
The 30–60 minute onset means regular insulin must be injected 30–45 minutes before eating to synchronise peak insulin action with peak postprandial glucose. Injecting at the same time as eating (as is acceptable with rapid-acting analogues) leads to hyperglycaemia during the meal and potential late hypoglycaemia when insulin finally peaks. This practical inconvenience — requiring pre-meal planning — is the primary reason rapid-acting analogues have largely displaced regular insulin for mealtime dosing in type 1 diabetes and intensively managed type 2 diabetes.
| Insulin Type | Examples | Half-Life SC | Onset | Peak | Duration |
|---|---|---|---|---|---|
| Rapid-acting analogue | Lispro, Aspart, Glulisine | ~1 hour | 10–15 min | 1–2 h | 3–4 h |
| Regular (short-acting) | Humulin R, Novolin R | ~2 hours | 30–60 min | 2–4 h | 5–8 h |
| NPH (intermediate) | Humulin N, Novolin N | ~4–6 hours | 1–2 h | 4–8 h | 12–18 h |
| Glargine (long-acting) | Lantus, Basaglar, Toujeo | ~12–19 hours | 1–2 h | Peakless | ~24 h |
| Route | Half-Life | Onset | Notes |
|---|---|---|---|
| Subcutaneous (abdomen) | ~2 hours | 30–60 min | Standard route; abdomen fastest absorption site |
| Subcutaneous (thigh/arm) | ~2 hours | Slower onset than abdomen | Thigh and arm slower; exercise accelerates absorption |
| Intravenous (IV) | ~5–15 min | Immediate | Approved for IV use (unlike most analogues); hospital/ICU only |
| Intramuscular (IM) | Faster than SC | ~15–30 min | Faster than SC; used historically in DKA management |
Regular human insulin is not detected by standard workplace immunoassay drug panels. WADA prohibits non-therapeutic insulin use in sport (S4 — Hormone and Metabolic Modulators).
Regular human insulin is structurally identical to endogenous human insulin, making it particularly difficult to distinguish from natural secretion by LC-MS/MS compared to synthetic analogues. C-peptide suppression testing is the primary method used by WADA-accredited laboratories to identify exogenous insulin use — exogenous insulin suppresses endogenous insulin and C-peptide secretion via negative feedback on pancreatic beta cells.
Regular human insulin is produced by recombinant DNA technology in E. coli or Saccharomyces cerevisiae, yielding a molecule identical in sequence to endogenous human proinsulin-derived insulin.[1] At the concentrations formulated in vials and pens (typically 100 U/mL), insulin strongly self-associates into zinc-coordinated hexamers. After subcutaneous injection, these hexamers form a semi-crystalline depot that dissociates gradually into dimers and monomers over 30–60 minutes — this is the rate-limiting step that explains the delayed onset.
Once absorbed into capillaries and the lymphatic system, regular insulin circulates bound loosely to proteins (primarily albumin, ~5%). It is cleared predominantly via receptor-mediated endocytosis at insulin receptors on hepatocytes (~60% first-pass hepatic extraction), with secondary clearance in the kidney and peripheral tissues. The liver's high first-pass extraction ratio means that SC insulin reaches peripheral tissues at approximately 40% of the portal concentration, while intravenous insulin bypasses hepatic first-pass and has a much shorter effective half-life (~5–15 min IV).
Log pre-meal injections and model regular insulin concentration curves based on the ~2-hour half-life. Visualise the 5–8 hour action window and plan meal timing. On-device. No data shared externally.
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