NPH insulin (isophane insulin)
Brand: Humulin N, Novolin N
ISMP High Alert Prototype: insulin-glargine
Drug Class: insulin
Drug Family: insulin
Subclass: intermediate-acting insulin
Organ Systems: endocrine
Mechanism of Action
Human insulin complexed with protamine to slow absorption from the subcutaneous injection site, producing an intermediate-acting profile with a distinct peak. Acts via the insulin receptor to promote cellular glucose uptake, suppress hepatic glucose production, and inhibit lipolysis.
insulin receptor (IR)
Indications
- type 1 diabetes mellitus
- type 2 diabetes mellitus
- gestational diabetes
Contraindications
- hypoglycemia
- hypersensitivity
Adverse Effects
Common
- hypoglycemia (especially 6–12 hours after injection)
- weight gain
- injection site reactions
Serious
- severe hypoglycemia
- hypokalemia
- anaphylaxis (rare)
Pharmacokinetics (ADME)
| Absorption | subcutaneous; onset 1–2 hours |
| Distribution | minimal protein binding |
| Metabolism | proteolytic degradation |
| Excretion | proteolytic |
| Half-life | variable |
| Onset | 1–2 hours |
| Peak | 4–8 hours |
| Duration | 12–18 hours |
| Protein Binding | minimal |
| Vd | low |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| beta-blockers | mask symptoms of hypoglycemia | moderate |
| corticosteroids | increase insulin requirements | moderate |
Nursing Considerations
- Cloudy appearance is expected; gently roll (do not shake) vial before use to ensure uniform suspension.
- Peak activity at 4–8 hours post-injection means patients are at highest hypoglycemia risk during this window; schedule meals accordingly.
- NPH is safe and preferred in pregnancy (gestational diabetes and pre-existing diabetes in pregnancy).
- NPH can be mixed with regular insulin (in same syringe); draw regular insulin first then NPH to avoid contaminating the regular insulin vial.
Clinical Pearls
- NPH remains widely used in resource-limited settings and in pregnancy due to its low cost and established safety data.
- The 4–8 hour peak creates a predictable window of hypoglycemia risk, particularly nocturnal if given at bedtime, requiring coordinated meal timing — a limitation compared to peakless analogs.
Safety Profile
Pregnancy safe
Lactation safe
Renal Adjustment Required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.