Key Facts

Insulin therapy is lifesaving in type 1 diabetes and commonly required in advanced type 2 diabetes. Insulin prescribing errors are among the most common and dangerous medication errors in hospitals.

Insulin Types

Pathophysiology

• T1DM: autoimmune destruction of beta cells → absolute insulin deficiency → essential for life
• T2DM: progressive beta-cell failure → eventually insufficient endogenous insulin → exogenous insulin needed
• Insulin: promotes glucose uptake (muscle, adipose), inhibits gluconeogenesis (liver), promotes lipogenesis, inhibits lipolysis
• Insulin deficiency: → hyperglycaemia + lipolysis → free fatty acids → ketogenesis → DKA

Type 1 Diabetes — Insulin Regimens

Basal-bolus (MDI — multiple daily injections):

• Long-acting OD (glargine) or BD (detemir) + rapid-acting with each meal
• Most flexible; gold standard; carbohydrate counting enables dose adjustment

Insulin pump (CSII):

• Continuous SC rapid-acting insulin infusion + bolus for meals
• NICE NG17: offer if MDI not achieving targets despite optimised management

Type 2 Diabetes — Insulin Initiation

• Basal insulin (glargine/detemir/degludec): start 10 units ON; titrate to fasting glucose target
• Continue metformin and SGLT2i; stop sulfonylurea
• Consider adding rapid-acting insulin pre-meals if postprandial control poor (basal-plus → basal-bolus)

Hypoglycaemia

• Mild (self-treatable): glucose <3.5 mmol/L; sweating, tremor, hunger, palpitations
• Severe (needs assistance): confusion, seizures, unconsciousness
• Nocturnal: waking with headache, confusion, sweating; may be unrecognised
• Impaired hypoglycaemia awareness: loss of warning symptoms — very dangerous; common in long-standing T1DM

Red Flags

• DKA: hyperglycaemia + ketones + metabolic acidosis → emergency (JBDS protocol)
• Severe hypoglycaemia → IV glucose 10% 200 mL or IM glucagon 1 mg
• Insulin omission in T1DM → DKA within hours
• Insulin overdose → prolonged hypoglycaemia; may need dextrose infusion for hours
• Prescribing errors: wrong insulin type, dose, or abbreviation — ensure 'units' written in full (not 'U')

Monitoring

• Capillary blood glucose (CBG): ≥4 times daily in T1DM (before meals and bedtime); more if unwell or adjusting doses
• Continuous glucose monitoring (CGM): Freestyle Libre, Dexcom — NICE NG17 recommends for T1DM; flash or real-time
• HbA1c: every 3–6 months; target 48 mmol/mol (6.5%) for T1DM; individualise
• Time in range (3.9–10.0 mmol/L): target >70% (emerging standard alongside HbA1c)

Before Starting Insulin

• Patient education: DAFNE (T1DM) or structured education programme
• Training: injection technique, site rotation, dose adjustment, hypoglycaemia recognition and management
• Driving: DVLA rules — must test glucose before driving and every 2 hours on long journeys

DKA Investigation

• Blood ketones: >3.0 mmol/L = DKA; monitor hourly
• VBG: pH, bicarbonate, lactate
• U&Es: potassium (may be high initially but falls rapidly with insulin; replace early)
• Blood glucose: often >14 mmol/L but can occur with near-normal glucose (euglycaemic DKA)
• FBC, CRP: infection as precipitant

T1DM — Basal-Bolus

• Basal: insulin glargine OD (start ~0.2–0.4 units/kg); titrate to fasting glucose 5–7 mmol/L
• Bolus: rapid-acting insulin with meals; dose based on carbohydrate counting (typically 1 unit per 10 g carb) + correction factor
• Total daily dose: typically 0.5–1.0 units/kg/day

T2DM — Insulin Initiation

• Basal insulin: start 10 units ON; increase by 2 units every 3 days until fasting glucose 5–7
• Continue metformin, SGLT2i
• Step up to basal-plus or basal-bolus if needed

Hypoglycaemia Management

Conscious:

• 15–20 g fast-acting carbohydrate (glucose tablets, Lucozade, fruit juice)
• Recheck glucose after 15 minutes; repeat if <4 mmol/L
• Follow with long-acting carbohydrate (toast, biscuit)

Unconscious/unable to swallow:

• IM glucagon 1 mg: community or hospital
• IV glucose 10% 200 mL (20 g): hospital; avoid 50% dextrose via peripheral cannula (extravasation injury)
• Continuous glucose infusion: if prolonged hypoglycaemia (e.g. sulfonylurea overdose)

DKA Management (JBDS Protocol)

• Fixed-rate IV insulin: 0.1 units/kg/hour soluble insulin (do NOT stop if patient is on SC basal insulin in T1DM)
• IV 0.9% saline: aggressive fluid replacement (1 L/hr for first 2 hours; slower thereafter)
• Potassium replacement: based on serum K+ (add 40 mmol/L KCl if K 3.5–5.5; omit if >5.5)
• Target: ketone reduction ≥0.5 mmol/L/hr; glucose reduction 3 mmol/L/hr
• Resume SC insulin: when eating/drinking AND ketones <0.6 AND pH >7.3; overlap IV and SC by 1–2 hours

Referral Criteria

• Diabetes specialist: T1DM management, pump therapy, recurrent DKA, pregnancy
• Diabetes nurse: insulin initiation education, dose adjustment
• DAFNE course: all T1DM patients — structured education in carb counting

• T1DM: near-normal life expectancy with good glycaemic control (DCCT/EDIC: intensive control reduces complications by 50–76%)
• T2DM on insulin: can achieve good control; progressive disease may require intensification
• Hypoglycaemia: leading barrier to achieving targets; impaired awareness affects ~20–25% of T1DM patients
• DKA mortality: ~1% in UK (higher in elderly, comorbidities, delayed presentation)
• Technology (CGM, insulin pumps): improving outcomes and quality of life

Insulin Regimen Summary

JBDS DKA Protocol Key Points