Insulin NPH (Isophane)

How it works

It acts on insulin receptors to increase glucose uptake and reduce hepatic glucose production; complexing with protamine forms a crystalline suspension that delays absorption, giving an intermediate duration with a defined peak.

Prescribing in practice

• As a suspension with a pronounced peak, NPH carries a notable risk of hypoglycaemia, particularly overnight.
• Resuspend gently by rolling the cloudy vial or pen before each injection to ensure a uniform, accurate dose.
• Rotate injection sites and review timing, as the peak action can be mistimed relative to meals or sleep.

Monitoring

Monitor capillary blood glucose, including overnight or pre-breakfast values, and HbA1c to guide titration.

Counselling the patient

• Gently mix the cloudy insulin until evenly milky before each dose.
• Carry fast-acting glucose and be especially alert to night-time hypoglycaemia.
• Rotate injection sites and never share pens or needles.

Evidence & guidelines

Isophane (NPH) insulin is a long-standing basal insulin option referenced in NICE diabetes guidance.