Insulin therapy in type 2 diabetes
Exam Tips
- In OSCE/viva, state clear indications for insulin in type 2 diabetes: symptomatic hyperglycaemia/catabolism, failure of maximal tolerated non-insulin therapy, or contraindication/intolerance to other agents.
- Know practical UK starting regimens: basal insulin often begins at 10 units once daily with structured titration every few days based on fasting glucose.
- Always mention safety counselling marks: hypoglycaemia recognition/treatment, driving advice, sick-day rules, injection technique, site rotation, and not sharing pens.
- If fasting glucose is controlled but HbA1c remains high, think post-prandial hyperglycaemia and discuss adding prandial insulin or switching to biphasic regimen.
- Examiners reward acknowledgment of barriers (needle anxiety, depression, frailty, dexterity/vision problems) and individualized targets to avoid harm.
Definition
Insulin therapy in type 2 diabetes is the planned use of exogenous insulin when endogenous insulin secretion is no longer sufficient to maintain safe glycaemia, or when non-insulin agents are unsuitable. In UK practice, it is introduced and titrated by clinicians with diabetes expertise after discussing benefits, hypoglycaemia risk, weight effects, driving implications, and patient preferences.
Pathophysiology
Type 2 diabetes combines insulin resistance (reduced peripheral glucose uptake and increased hepatic glucose output) with progressive beta-cell failure, so both basal and meal-stimulated insulin secretion decline over time. Early disease may respond to lifestyle and oral/injectable non-insulin drugs, but advancing beta-cell dysfunction causes persistent hyperglycaemia, catabolic symptoms, and rising microvascular/macrovascular risk, prompting insulin initiation. Physiologically, replacement aims to mimic basal insulin background plus prandial peaks; clinically this is delivered as basal-only, biphasic, or basal-bolus regimens (See Figure: physiological basal-bolus insulin secretion curve in endocrine physiology texts).
Risk Factors
- Longer duration of type 2 diabetes with progressive beta-cell exhaustion
- Marked hyperglycaemia with osmotic/catabolic symptoms (polyuria, polydipsia, weight loss)
- Failure to reach glycaemic targets despite maximal tolerated non-insulin therapy
- Contraindication or intolerance to oral/non-insulin glucose-lowering drugs
- Younger patient with high lifetime risk of complications from prolonged hyperglycaemia
Clinical Features
Symptoms
- Polyuria
- Polydipsia
- Nocturia
- Unintentional weight loss
- Fatigue
- Blurred vision
Signs
- Persistent raised capillary glucose/HbA1c despite treatment
- Features of dehydration in severe hyperglycaemia
- Catabolic phenotype (weight loss, reduced muscle mass)
- Diabetes complications already present (for example retinopathy, neuropathy)
Investigations
Management
Lifestyle Modifications
- Structured diabetes education before and during insulin start (injection technique, storage, site rotation, hypo recognition, sick-day advice).
- Individualized nutrition and weight-management support to reduce insulin-associated weight gain.
- Physical activity plan with glucose monitoring strategy to prevent exercise-related hypoglycaemia.
- Driving/travel counselling, including carrying fast-acting carbohydrate and glucose monitoring before driving.
Pharmacological Treatment
Basal human insulin (first-line basal option in many UK pathways)
- Isophane insulin (NPH; e. g, Insulatard or Humulin I) start 10 units at bedtime (or 0.1-0.2 units/kg once daily), then titrate every 3-4 days using fasting glucose.
Common initiation strategy in UK practice; continue metformin if tolerated. Main risks: hypoglycaemia and weight gain. Ensure device-specific training and clear unit-based prescribing to reduce insulin error.
Basal insulin analogues
- Insulin glargine (100 units/mL) start 10 units once daily, titrate to fasting target.
- Insulin detemir start 10 units once daily (sometimes twice daily if needed).
- Insulin degludec start 10 units once daily.
Useful when nocturnal hypoglycaemia risk is problematic or once-daily convenience is needed. Do not interchange products by brand/concentration without explicit review; concentration errors (e. g, U100 vs U200) are a key safety hazard.
Premixed (biphasic) insulin
- Biphasic isophane/regular insulin (e. g, Humulin M3) often start 10 units once or twice daily with meals.
- Biphasic insulin aspart (e. g, NovoMix 30) often start 10 units with largest meal, then intensify to twice daily if required.
Consider when both fasting and post-prandial glucose are elevated and simpler regimens are preferred. Requires regular meal timing; hypoglycaemia risk rises with missed meals.
Basal-bolus intensification
- Add rapid-acting insulin (e. g, insulin aspart, lispro, or glulisine), often beginning with 4-6 units (or ~10% of basal dose) with largest meal, then stepwise addition to other meals as needed.
For persistent post-prandial hyperglycaemia on optimized basal insulin. Requires frequent SMBG, carbohydrate-awareness education, and close dose titration.
Co-therapy considerations and safety
- Metformin usually continued if tolerated and not contraindicated.
- Sulfonylurea dose reduction or cessation may be required when insulin is started to reduce hypoglycaemia.
Important cautions: recurrent severe hypoglycaemia, frailty/cognitive impairment, reduced manual dexterity or vision, and limited life expectancy may shift targets and regimen intensity. Pioglitazone with insulin can worsen fluid retention/heart failure risk; avoid in heart failure. Counsel on DVLA rules for insulin-treated drivers and strict hypo avoidance before/during driving.
Complications
- Hypoglycaemia (including severe episodes requiring third-party assistance)
- Weight gain after insulin initiation
- Injection-site lipohypertrophy causing erratic insulin absorption
- Falls, confusion, and injury risk in frail older adults after hypoglycaemia
- Medication/device errors (wrong insulin type, wrong concentration, wrong timing)
- Persistent hyperglycaemia if therapeutic inertia delays titration or intensification
Prognosis
When insulin is introduced promptly and titrated safely, glycaemic control and symptom burden usually improve, with reduced long-term microvascular risk. Prognosis is poorer when initiation is delayed, adherence is limited by psychological or functional barriers, or recurrent hypoglycaemia prevents adequate dose optimization.
Sources & References
💊BNF Drug References(7)
- Alogliptin[management.pharmacological]
- Canagliflozin[management.pharmacological]
- Dulaglutide[management.pharmacological]
- Ertugliflozin[management.pharmacological]
- Exenatide[management.pharmacological]
- Insulin degludec with liraglutide[management.pharmacological]
- Lixisenatide[management.pharmacological]
✅NICE Guidelines(1)
- Insulin therapy in type 2 diabetes[overview]