Medicines dosing errors and how to avoid themMedication is a fundamental part of healthcare. A record 1.16 billion prescription items were dispensed by community pharmacies in England alone in the year 2024/25¹ and 8.4 million people in the UK are known to regularly take five or more medicines.²
Medication is a fundamental part of healthcare. A record 1.16 billion prescription items were dispensed by community pharmacies in England alone in the year 2024/25¹ and 8.4 million people in the UK are known to regularly take five or more medicines.²
For medicines to be effective and safe, good prescribing practice is critical; a medicine should always be appropriate for the patient and given in the correct dose.
With such widespread use of medicines, however, there is inevitably a risk of errors. Medication errors are a frequent and avoidable source of patient harm.³ A recent study estimated that 237 million errors occur at some point in the medication process in England annually, causing or contributing to 1708 deaths and with a projected cost of over £98M each year.³ The World Health Organization (WHO) suggests that nearly 50% of preventable harm to patients globally is due to inappropriate use of medicines and a quarter of this can be severe or even life-threatening.⁴
Dosing errors are a frequent type of medication error⁵ ⁶ ⁷ and preventing them is paramount for patient safety. In this article we explore how they occur, their potential impact on patient outcomes, and the strategies we can employ to avert them and improve medication safety in all healthcare settings.
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Medication errors related to dosing
Medication errors can occur at any stage in the medicines use process: ordering or prescribing, transcribing, preparation and dispensing, administration, or monitoring of a medicine.⁴
The literature shows that dosing errors are extremely common and can arise at any of these stages.
A US study found that 41% of 469 fatal medication errors involved the wrong dose of a medicine being given.⁵ In an analysis of medication incidents in England the wrong dose accounted for 28.7% of almost 60,000 incidents reported to the National Patient Safety Agency (NPSA) between January 2005 and June 2006.⁶
A dosing error usually leads to a patient taking too little or too much of a medicine. Administering a sub-therapeutic dose is likely to mean that the medicine will not have the required effect. Intended doses can also be missed due to error. On the other hand, giving higher than the required dose or extra doses can lead to harm due to drug toxicity or enhanced side effects. Harm due to medication errors, including dosing errors, is more likely in children, the elderly, people with comorbidities, poor renal or hepatic function and those taking multiple medicines (i.e. polypharmacy).⁴
Prescribing errors
Across all healthcare settings, a high proportion of dosage errors occur at the prescribing stage.⁸ ⁹
It is critical that the correct dose of a medicine is selected for a patient; the optimal dose being the dose that gives the desired effect with minimal side effects. Dosing is influenced by medication factors (such as the pharmacokinetics, pharmacodynamics, therapeutic index, route of administration and formulation) and patient factors, including age, medical history, weight, sex, ethnicity, and renal and hepatic function. The other medicines a patient is taking are also important due to the risk of drug interactions, as these often requires adjustment of the standard recommended dose. A good understanding of all these factors is essential for determining the appropriate dose.
Some medicines pose a greater risk of harm due to dosage errors than others.¹⁰ ¹¹ ¹²
Error rates with these ‘high risk’ drugs are not necessarily higher than with other medicines, but when problems occur, the consequences can be more significant. There are many such high risk medicines, including opioids, hypoglycaemics, anticoagulants, cytotoxic drugs, non-steroidal anti-inflammatory drugs (NSAIDs), antiplatelets, diuretics, corticosteroids, and cardiac glycosides. A systematic review of the prevalence and incidence of prescribing errors with high-risk medicines in hospitals found a highly variable prevalence, perhaps because of different definitions of both prescribing errors and high risk medicines (ranging from 0.24 to 89.6 errors per 100 prescriptions).¹³ The commonest type of error identified was dosage error. Of concern, the three highest prevalence rates were observed in studies in children, with the most common error being a child’s weight not recorded or incorrectly recorded.
Other dosing errors
There is no standard way of categorising dosage errors and there is some ‘cut-across’ with different types of medication error. Other than prescribing an incorrect dose, common dosing errors include:
- Incorrect strength
Selection of the incorrect strength of a medicine is common during the dispensing and administration stages and can cause severe harm.⁶ This is often due to mis-selection of a drug from a list or prescription but is also common at transitions of care i.e. from hospital to primary care. Decimal points can be misinterpreted (e.g. giving 5mg when 0.5mg was intended) or dosage units can be confused (e.g. micrograms and milligrams). - Incorrect timing, dosing frequency or administration rate
Mistakes in the timing, frequency or rate of medication administration can lead to drug toxicity or therapeutic failure. A common example with potentially fatal consequences is inadvertent daily dosing of methotrexate instead of weekly dosing.¹⁴ Giving a parenteral medicine, such as an IV bolus or infusion, at the wrong rate of administration can also be clinically significant. The result may be adverse drug reactions such as tachycardia with IV epinephrine or flushing syndrome when vancomycin is given rapidly.¹⁵
- Calculation errors
Mistakes when calculating drug doses are also common. These calculations may require accuracy in converting units of measurement and up to date patient parameters such as weight and organ function. Calculation errors are especially common with injectable medicines as these often require complex dose calculations for individual patients.¹⁶ - Incorrect formulation or dosage form
Where several formulations of a medicine are available, errors in the dose, frequency, or duration of treatment can occur. For example, the alkylating agent etoposide is available in two different intravenous formulations, the etoposide base and the etoposide phosphate salt, which are not equivalent. Dosage errors are possible if these differences are not taken into account.¹¹ - Patient or carer error
In many cases, patients themselves (or their caregivers), make mistakes in the administration of the medication, including using the wrong dose.¹⁷ One important example relates to unintentional overdose of fentanyl, due to errors made by patients or caregivers.¹⁸ This emphasises the importance of patient counselling and referring to patient information leaflets.
Factors contributing to dosing errors
The causes of dosing errors are essentially the same as those for medication errors in general and are multi-faceted.⁴ ¹⁹ They include:
- Medicine factors
The appearance of the medicine itself may contribute to errors. “Look alike, sound alike” (LASA) medicines, unclear or misleading labelling or similar packaging may lead to dosage errors. - People factors
The knowledge and skills of health professionals, including awareness of medicines errors and their prevention, are important in minimising risks to patients. Failure to adhere to safe working practices, for whatever reason, can cause errors. - System and process factors
Poorly designed systems, gaps in processes and impractical working practices contribute to medication errors. Workload pressures due to limited resources and time constraints can compromise attention to detail. Lack of clarity about actions to be taken, or who is responsible for taking action, leaves room for errors to occur.
Several health professions are involved in the journey of a medicine from supply to the point of administration to the patient. Poor communication is known to be a major driver of medication errors, whether written communication such as incomplete or incorrect documentation or poor verbal handovers of patient care.²⁰ Collaboration is essential to understand the use of the medicine from the perspectives of a range of professionals.
Essential components of good practice for medication safety include:
- Robust dose checking systems for all those involved in prescribing, dispensing, and administering medication.
- Good communication and collaboration among health professionals involved in patient care.
- Effective medicines reconciliation processes, particularly during transitions of care.
- Up-to-date clinical decision support systems (i.e. electronic prescribing systems with alerts and reminders)
- Ensuring that patients and their carers are well informed about the medicines they are taking, including the correct dose, and the importance of medication adherence.
- Regular medication reviews that involve and empower patients.
- A culture of safety and continuous quality improvement that involves education, learning from error and reporting errors to the most appropriate organisation or group.
Resources to support health professionals with appropriate drug dosing include:
- British National Formulary (BNF) and BNF for Children (BNFC)
- Stockley’s Drug Interactions and Stockley’s Interactions Checker
- Drug Monitoring Checker
Addressing the challenges of medication errors, including those related to dose, should be a priority in healthcare settings to ensure patient safety and the best possible treatment outcomes.
Effective communication and collaboration between health professionals can support good medication safety practices to minimise the risk of error.
By using reliable, evidence-based sources of prescribing information, health professionals can ensure the correct dose is used, thereby avoiding medication errors and improving overall patient care.
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References
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