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ukmla 2026

Insulin Prescribing and Errors

Insulin is a high-risk medication — prescribing errors (wrong dose, wrong type, wrong timing) and management errors (omission in hospital) are common causes of preventable hypoglycaemia and DKA

Review date
reviewed 2026-04-05
Reading time
4 min read
Author
Dr Kola Tytler MBBS CertHE MBA MSt MRCGP
Clinical Pharmacologycommonacute
On this page
Condition details
Clinical Pharmacology
common
4 min read
reviewed 2026-04-05
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About This Page

This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.

Key points

  • Insulin is a PINCH drug (highest risk for medication errors) — NEVER abbreviate "units" as "U" (misread as "0" = 10-fold overdose)
  • Know the insulin types: rapid-acting (NovoRapid, Humalog), short-acting (Actrapid), intermediate (Insulatard, Humulin I), long-acting (Lantus, Levemir, Tresiba), biphasic (NovoMix 30, Humulin M3)
  • NEVER omit basal insulin in hospital — even if patient is nil-by-mouth, basal insulin should continue (may need dose reduction)
  • Variable rate insulin infusion (VRII, "sliding scale"): for acutely unwell diabetic patients who cannot eat — always continue background basal insulin alongside VRII
  • Insulin errors cause approximately 2,000 severe hypoglycaemia incidents per year in UK hospitals

Overview

Insulin prescribing errors are among the most common and dangerous medication errors in hospital practice. The National Patient Safety Agency (NPSA) and NHS England have issued multiple alerts regarding insulin safety. Common errors include: wrong dose (10-fold errors from misreading "10 units" as "100 units"), wrong insulin type (confusion between rapid-acting and long-acting), wrong timing (giving rapid-acting insulin without food), omission of insulin in hospital (leading to hyperglycaemia and DKA in type 1 diabetes), and inappropriate use of variable rate insulin infusions without concurrent basal insulin. All insulin prescriptions should use insulin-specific syringes/pens, and doses should be double-checked.

Epidemiology

Approximately 4 million people in the UK have diabetes, with around 1 million requiring insulin. NHS England data shows insulin is consistently among the top drugs causing severe harm in hospital. An estimated 2,000 severe hypoglycaemic episodes per year in hospital are attributable to insulin prescribing or administration errors. The Joint British Diabetes Societies (JBDS) have published comprehensive inpatient insulin management guidelines to standardise practice.

Clinical Features

Symptoms
Hypoglycaemia from overdose or wrong timing: sweating, tremor, confusion, seizures, coma
Hyperglycaemia/DKA from omission: polyuria, polydipsia, vomiting, abdominal pain, Kussmaul breathing
Signs
Signs of hypoglycaemia: sweating, tachycardia, tremor, confusion, reduced GCS
Signs of DKA: dehydration, tachypnoea (Kussmaul breathing), ketotic breath, abdominal tenderness

Investigations

First-line
Capillary blood glucoseRegular monitoring — frequency depends on regimen and clinical status (typically QDS for basal-bolus, hourly for VRII)
Blood ketonesIf blood glucose >14 mmol/L in type 1 diabetes or acutely unwell — ≥3.0 mmol/L indicates DKA
Second-line
HbA1cAssess long-term glycaemic control — guides insulin dose adjustment
VBGIf DKA suspected — assess pH, bicarbonate, potassium

Management

JBDS Inpatient Insulin Guidelines + NPSA/NHS England Insulin Safety Alerts
1
Insulin types (essential knowledge)
  • Rapid-acting (onset 15 min, duration 3–5h): NovoRapid (insulin aspart), Humalog (insulin lispro), Apidra (insulin glulisine) — give with meals
  • Short-acting (onset 30 min, duration 6–8h): Actrapid, Humulin S — give 20–30 min before meals
  • Intermediate (onset 1–2h, duration 12–18h): Insulatard, Humulin I — usually BD
  • Long-acting (onset 1–2h, duration 20–36h): Lantus (glargine), Levemir (detemir), Tresiba (degludec) — once or twice daily, provides basal coverage
  • Biphasic/premixed (combination of rapid + intermediate): NovoMix 30, Humulin M3 — usually BD with meals
2
Prescribing safety rules
  • NEVER abbreviate "units" as "U" — write "units" in full (prevents 10-fold errors)
  • Always use insulin-specific syringes (100 units/mL) — NEVER use non-insulin syringes
  • Prescribe by BRAND NAME not generic (different insulin brands are NOT interchangeable)
  • Always specify dose, type, timing, and route
  • Double-check dose with another healthcare professional before administration
3
Inpatient insulin management
  • NEVER omit basal (long-acting) insulin — even if nil-by-mouth. May reduce dose by 20% if not eating
  • If patient can eat: continue usual basal-bolus or biphasic regimen
  • If patient is nil-by-mouth or acutely unwell: start VRII + continue basal insulin at reduced dose
  • VRII ("sliding scale"): insulin infusion titrated to hourly blood glucose. Run alongside glucose-containing IV fluids
  • Switch back to SC insulin BEFORE stopping VRII — give SC dose 30–60 min before disconnecting infusion
4
Sick day rules for patients
  • NEVER stop insulin during illness (even if not eating) — insulin requirements often INCREASE during illness
  • Monitor blood glucose every 2–4 hours and blood ketones regularly
  • Drink plenty of fluids
  • Seek medical advice if: blood ketones >3.0 mmol/L, persistent vomiting, or blood glucose persistently >14 mmol/L

Complications

  • Severe hypoglycaemia: Seizures, coma, brain damage, death — from insulin overdose or wrong timing
  • DKA: From insulin omission in type 1 diabetes — can develop within hours
  • Lipohypertrophy: Lumps at injection sites from not rotating — causes erratic absorption
UKMLA Exam Tips
  • 1NEVER abbreviate "units" as "U" — classic patient safety question. Write "units" in full
  • 2NEVER omit basal insulin in hospital — even if nil-by-mouth (reduce by 20% but do NOT stop)
  • 3Prescribe insulin by BRAND NAME — different brands are NOT interchangeable
  • 4VRII should ALWAYS be accompanied by basal insulin — VRII without basal = risk of DKA when VRII stopped
  • 5Know the key insulin types: Lantus = long-acting (OD), NovoRapid = rapid-acting (with meals), NovoMix 30 = biphasic (BD)
  • 6Sick day rules: NEVER stop insulin during illness. Requirements usually INCREASE (stress hormones)
  • 7Switch from VRII to SC insulin: give SC dose 30–60 min BEFORE stopping the infusion

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Verified Sources & References

JBDS — Inpatient Insulin Management Guidelines
NHS England — Insulin Safety Alerts
BNF — Insulin
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