Types of Insulin: Which One and Why

The 5 Types of Insulin

Basal-Bolus Regimen (Type 1 Diabetes)

The most physiological insulin regimen mimics the body's natural insulin secretion:

• Basal insulin (once or twice daily): Provides background insulin, e.g. Lantus at bedtime
• Bolus insulin (with each meal): Rapid-acting insulin to cover carbohydrate content, e.g. NovoRapid with each meal
• Correction doses: Extra bolus to bring high blood sugar back to target

Injection Sites and Rotation

Recognising and treating hypoglycaemia

Hypoglycaemia (blood glucose below 4.0 mmol/L / 72 mg/dL) is the most common acute complication of insulin therapy. It is preventable and almost always treatable at home if recognised early.

Warning signs: sweating, tremor, palpitations, anxiety (adrenaline surge, usually when glucose drops below 3.5 mmol/L); then – if untreated – confusion, blurred vision, difficulty speaking, and eventually seizure or loss of consciousness (neuroglycopaenia below ~2.5 mmol/L).

The 15–15 rule: Treat mild to moderate hypoglycaemia with 15 g of fast-acting carbohydrate (a small glass of fruit juice, 5–6 glucose tablets, or 4–5 jelly babies), wait 15 minutes, and recheck blood glucose. If still below 4.0 mmol/L, repeat. Follow up with a long-acting carbohydrate snack (a biscuit, toast) to prevent recurrence.

Severe hypoglycaemia: If the person is unconscious or cannot swallow, a bystander should administer intramuscular glucagon (1 mg; available as a kit on prescription) or call emergency services for intravenous glucose. Never give anything by mouth to an unconscious person.

Storage and shelf-life

Incorrect storage is a leading cause of unexpected hypoglycaemia and hyperglycaemia. Key rules:

• Unopened insulin: Store in the refrigerator (2–8°C / 36–46°F). Do not freeze; frozen insulin is degraded and must not be used.
• In-use insulin: Once opened or removed from the fridge, most insulin formulations are stable at room temperature (below 25–30°C) for 28–30 days. Check the specific product information – some analogue insulins (e.g., insulin degludec) can be stored at room temperature for up to 8 weeks.
• Heat and sunlight: Avoid direct sunlight or temperatures above 30°C (86°F); this accelerates degradation. In hot climates, a small insulated case or a Frio cooling wallet (activated by water) protects in-use pens during travel.

Sick day guidance on insulin

Illness – especially infections – typically raises blood glucose due to stress hormones, even when the person is not eating. This is the opposite of what many people expect. The rule of thumb is: never stop insulin during illness. Insulin requirements may actually increase. People with type 1 diabetes should check blood glucose and ketones every 2–4 hours during illness and contact their diabetes team if:

• Blood glucose exceeds 15 mmol/L (270 mg/dL) despite extra correction doses.
• Blood or urine ketones are moderate or high.
• They cannot keep any fluids down for more than 1–2 hours.

References

Sources cited on this page. PubMed links open the original abstract.

1. Hirsch IB. Insulin analogues. N Engl J Med. 2005;352(2):174–183. PMID 15647580 · doi:10.1056/NEJMra040832