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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
- Medication errors affect ~10% of hospital prescriptions — most are at prescribing stage, followed by administration
- PINCH drugs (highest risk): Potassium IV, Insulin, Narcotics (opioids), Chemotherapy, Heparin/anticoagulants
- Medication reconciliation at every care transition (admission, transfer, discharge) is a key safety intervention
- Always check: allergy status, renal/hepatic function, interactions, correct dose/route/frequency, pregnancy/breastfeeding status
- WHO 3rd Global Patient Safety Challenge: "Medication Without Harm" — aims to reduce severe avoidable medication harm by 50%
Overview
Prescribing errors are unintentional deviations from appropriate prescribing practice that may lead to patient harm. They occur at multiple stages: prescribing (commonest), dispensing, administration, and monitoring. Common error types include wrong dose, wrong drug, wrong route, wrong patient, omission, drug interactions, and failure to adjust for renal/hepatic impairment. High-risk medications (PINCH drugs) require additional safety checks. Systems-based approaches (electronic prescribing, clinical decision support, standardised protocols, medication reconciliation) reduce error rates.
Epidemiology
The EQUIP study found that ~9% of hospital prescriptions contain errors, with approximately 2% being potentially lethal. Foundation year doctors and those prescribing unfamiliar medications are at highest risk. Approximately 237 million medication errors occur annually across NHS England. The annual cost of medication errors to the NHS is estimated at £98 million. Prescribing errors contribute to approximately 1,700 deaths annually in the UK.
Clinical Features
Symptoms
Wrong dose (10-fold errors are classic — e.g. decimal point errors with insulin or opioids)
Wrong drug (look-alike/sound-alike: chlorproMAZINE vs chlorproPAMIDE)
Wrong route (e.g. oral medication given IV, intrathecal vincristine)
Omitted medications (e.g. missing anticoagulant, missed steroid in patient on long-term steroids)
Drug interactions not identified (e.g. macrolide + statin, warfarin + NSAID)
Failure to adjust dose for renal impairment (e.g. metformin, DOACs, gentamicin)
Allergy not checked (prescribing penicillin to a patient with documented penicillin allergy)
Signs
Signs depend on the specific error — hypoglycaemia (insulin), bleeding (anticoagulants), sedation (opioids)
Investigations
First-line
Medication reconciliationCompare current medications against prescriptions at every care transition — identify discrepancies, omissions, duplications
Drug chart reviewSystematic review of all prescriptions: dose, frequency, route, allergy band, renal/hepatic function check
Second-line
Incident reporting (Datix/NRLS)Report all medication errors and near-misses — promotes learning and system improvement
Root cause analysisFor serious medication errors — identify system and human factors contributing to the error
1
Prevention strategies
- Always check: right Patient, right Drug, right Dose, right Route, right Time (5 Rs)
- Check allergy status before EVERY prescription
- Use electronic prescribing (EPMA) with clinical decision support where available
- Check renal function (eGFR) and hepatic function before prescribing renally/hepatically cleared drugs
- Avoid abbreviations: write micrograms not mcg, units not U, do not use trailing zeros
2
High-risk medications (PINCH)
- Potassium IV: never give as bolus, max 10 mmol/hour peripherally, cardiac monitoring required
- Insulin: always double-check dose, use insulin-specific syringes, never abbreviate "units" as "U"
- Narcotics (opioids): use mg not mL, start low and titrate, prescribe naloxone for at-risk patients
- Chemotherapy: must be prescribed by oncology, independent double-checking, intrathecal vincristine protocols
- Heparin/anticoagulants: weight-based dosing, APTT monitoring for UFH, check platelets for HIT
3
When an error occurs
- Immediate clinical assessment of the patient — harm or potential harm?
- Treat any adverse effects urgently
- Duty of candour: inform the patient honestly and apologise
- Report via incident reporting system (Datix)
- Complete root cause analysis for serious incidents
Complications
- Patient harm or death: Most serious consequence — e.g. wrong dose of insulin, intrathecal vincristine
- Prolonged hospitalisation: From managing ADR consequences
- Medicolegal consequences: Negligence claims, GMC referral, coroner investigations
- Loss of patient trust: If errors are not disclosed honestly (duty of candour)
UKMLA Exam Tips
- 1PINCH drugs: Potassium IV, Insulin, Narcotics, Chemotherapy, Heparin — highest risk medications
- 2Medication reconciliation should happen at EVERY care transition (admission, ward transfer, discharge)
- 3Decimal point errors are a classic exam scenario — 0.5 mg misread as 5 mg = 10-fold overdose
- 4Duty of candour: you MUST tell the patient when something has gone wrong
- 5Never abbreviate "units" as "U" (can be misread as "0") or "micrograms" as "µg" (misread as "mg")
- 6Intrathecal vincristine is ALWAYS fatal — now given only in a minibag (not a syringe) to prevent wrong-route errors
- 7Always check: allergy, renal function, hepatic function, pregnancy, interactions BEFORE prescribing
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