Common Prescribing Errors

When I supervise and teach FY1s, prescribing is among the top three things they are most concerned about. Usually, they’re worried that they won’t know what to prescribe or that an error will cause serious harm. As with everything, your seniors have all been through this and we are here to help you through.


The GMC did an interesting investigation looking at drug errors which revealed:

  • F1s make about the same number of errors as their senior colleagues (about 8-10% of prescriptions with FY2s being the worst offenders due to misplaced confidence)
  • Errors across all grades are about equally serious (potentially serious: about 5%, potentially lethal: about 1-2%)
  • Errors are most common in the drugs used the most: analgesics, antibiotics, cardiac drugs (antianginals, hypertension, heart failure), steroids and anticoagulants
  • The most common types of drug errors are:
    • Omission (either during admission or on discharge)
    • Incorrect dosing (either too high/low or incorrect timings)
    • Duplication

Teaching on prescribing focuses on F1s because they do far more prescriptions than their senior colleagues (over 60% is done by FY doctors). With about 50% of hospital admissions affected by prescribing errors, it is vital that new doctors get it right & adopt good prescribing habits early on.

Causes of errors are multifactorial – it isn’t just a lack of knowledge but also rule-based errors – usually when a good rule (e.g. add potassium to maintenance fluids) is incorrectly applied (e.g. to a patient with high potassium).

With all this in mind, here are some tips:

Tip 1: Working conditions can increase errors

Ensure you’re aware of your stress levels as a busy ward, low staffing levels, unsupportive seniors & poor drug chart design can all increase your risk of prescribing errors.

If you read interviews of F1s that have made drug errors, a common theme is stress & pressure contributed to the error.

Have a read on managing work-life balance to identify when you are stressed and put in safeguards to manage this.

Tip 2: Always check allergies before prescribing

Whilst this is obvious, it can be really hard to remember when you’re pressed on a ward round and your consultant says “Prescribe this…”

Get in the habit of always checking allergies before every prescription – even things you think they couldn’t possibly be allergic to. The red allergy band worn by patients can be a helpful reminder.

Tip 3: Always review the drug chart before prescribing

  • Check the name & details. It is way too easy to prescribe for the wrong patient.
  • Look if the drug is already prescribed or whether it (or a similar drug) is part of their usual drug history (can be found on the admission clerking, electronic records or drug reconciliation by pharmacists)
  • Check whether any other drugs they are usually on have been omitted & take a moment to look for any errors
  • Check if any drugs need levels monitoring (e.g. aminoglycosides)
  • Consider frequent drug interactions (Interaction checkers: Medscape & BNF)
    • Those that potentiate adverse effects e.g. prolonged QT
    • Common drug metabolism inhibitors or inducers

It simply isn’t possible nor helpful to cover every interaction (and even the list of common ones is far too long!), therefore, use the interaction checker, your medical school knowledge and your pharmacist. I’m a fan of the Medscape interaction checker as you can simply list all the drugs the patient is on with ease.

Tip 4: Always look up an unfamiliar drug

Whether the drug is already prescribed or you are about to prescribe it, look it up in the BNF. This is a fantastic learning opportunity but also ensures you can look up common adverse effects & issues associated with it. Even consultants use the BNF all the time – you’re definitely not expected to know it all!

Tip 5: There are people that can help

Even now, when I’m mere months away from being a medical registrar, I still ask for help from colleagues and pharmacists when it comes to prescribing. Don’t ever feel “Oh, I’m being silly asking” – because you’re there to learn and all your prescribing is meant to be supervised.

I can’t stress how amazing pharmacists are. They usually endorse every prescription you make (although usually not immediately) and so they have a vested interest that you get it correct. Conversely, ensure you don’t assume nurses or pharmacists will check your prescriptions – they are often not checked for over 24 hours if not longer. Overdependence on safety mechanisms is even more dangerous.

Tip 6: Consider their weight & renal function

Weight: Medications such as VTE prophylaxis, paracetamol intravenously (if <50kg), IV fluids, aminoglycosides and many others require adjusting for weight.Renal function: Many medications need to be held or adjusted in AKI & CKD based on renal function e.g. metformin, NSAIDs, antibiotics, opiates, anticoagulants. The renal drug handbook is excellent.A simple rule of always checking the drug chart in patients with low weight or poor renal function for medications that need to be adjusted!

Tip 7: Caution in the elderly

Polypharmacy in frail elderly patients is a big concern. They are more susceptible to falling and so any sedating medications, antihypertensive, anticholinergic (affecting cognition), insulin, statins (myopathy) need careful consideration. They are also far more likely to accumulate medications from their poor renal function, which means many drugs might need to be reviewed e.g. aminoglycosides and digoxin. Unfortunately, as they’re on so many medications often things can be missed. Many tools exist to identify drugs that might be inappropriate in the elderly: Beers criteria, STOPP START (See Pg 23 of 28).

Tip 8: Caution when a patient is nil by mouth

It can be dangerous to stop critical drugs e.g. antiepileptics, Parkinson’s medication, antipsychotics, steroids, opiates, b-blockers. Therefore, whenever you or your seniors recommend for a patient to be nil by mouth, clarify whether this includes all medication. If it does, consider whether a nasogastric tube is suitable or parenteral formulations are required for each medication. Ensure you ask a pharmacist to support you as not all medications can be crushed (modified release formulations for example) or switched over & some may need dose adjustment. For Parkinson’s medication, our article includes advice on conversions & a link to a calculator.

Tip 9: Recognise your limitations

Ensure you know what the prescription restrictions are in your trust.FY1s (and often SHOs) often cannot prescribe cytotoxics, immunosuppressants (other than steroids) or anticancer/chemotherapy agents but this varies by trust. This is because they’re difficult medications to prescribe, new doctors are frequently unfamiliar with them & incorrect prescribing can be life-threatening (the infamous daily methotrexate). However, it is important to extend this logic as lots of medication can be equally dangerous. Be aware that you aren’t always expected to know the right answer and that you will need to ask about safety of medications outside of these complex drugs. Although as an SHO I have the ability to prescribe all of the above agents, I very rarely will without discussing these with my seniors.

Finally, do bear in mind that as an FY1 you cannot complete outpatient or private prescription forms including FP10s.

Tip 10: Avoid rote behaviour

A bat and a ball cost £1.10 in total. The bat costs £1.00 more than the ball. How much does the ball cost?

Often people will answer saying the ball costs 10p which is wrong. Although intuition makes us faster, it can be inaccurate when we unconsciously react rather than think things through.

In terms of prescribing, as a new doctor it can be dangerous to prescribe automatically when you’re not so familiar with the nuances of when prescriptions might be dangerous. Let’s review a patient’s journey exploring how this might occur:

On admission, you continue a patient’s ACE inhibitor even though they have acute kidney injury & hypotension.

During the admission, you note a patient’s VTE prophylaxis hasn’t been prescribed. You prescribe this missing that the patient has been having excessive rectal bleeding.

On discharge, you prescribe co-codamol on their discharge summary as you do for every post-surgical patient. This patient was taking codeine on admission and therefore has both prescribed.

When you find yourself automatically prescribing something, being aware that you are doing this can reduce your likelihood of making mistakes by taking a moment to:

  • Check your work
  • Think about any issues with what you’ve prescribed
  • Engage with all the other things recommended in this article

For written prescriptions, be careful you write milligrams or micrograms in full to avoid them being mixed up. Confusing these could result in dangerous overdoses.

For electronic prescribing, be careful you select the right drug e.g. when searching “Am”, “Amlodipine” & “Amiloride” may both come up. It can also be easy to select the wrong type of tablet (immediate release vs modified release), incorrect formulation or dosing times.
For discharge, ensure you review each prescription rather than simply coping the inpatient drug chart.

Special Considerations for Common Drugs

  • Use Microguide and/or discussions with Microbiology to ensure you use the right antibiotic for the right infection & patient
  • Don’t forget to include the stat dose for antibiotics – this is especially problematic for e-prescribing which might default to the usual administration time e.g. 8am/2pm/10pm for TDS dosing – delaying the first dose until then
  • Review daily whether antibiotics can be stopped, changed for a narrower spectrum or stepped down to oral (reducing risk of c diff, length of stay & adverse effects)
  • When using aminoglycosides (gentamicin, amikacin), ensure you review the therapeutic drug monitoring guidelines and check levels (handing these over when appropriate)
  • Don’t forget to check allergies e.g. penicillin
  • Read more here
  • Common issues include not reviewing renal function, platelets, weight & bleeding risk factors
  • For warfarin, ensure you check the INR regularly & consider drug interactions that increase or decrease the INR
  • Consider whether a DOAC is more suitable if INR is frequently out of range or monitoring is inconvenient for the patient (factoring in lifestyle, cognition, drug interactions or adherence issues that might influence this choice)
  • Ensure patients are educated to avoid interactions & inform healthcare professionals with follow up with the anticoagulation team if required
  • Insulins come many different types: they vary in concentration (usually 100 units/ml) and duration of action (short, intermediate & long-acting and mixed) so make sure you clarify exactly which type the patient takes
  • When in doubt check with the patient, healthcare records, the pharmacist or next of kin
  • Never write “u” as this can be misread for zero – instead, write “UNITS”
  • Do involve the diabetes nurse specialists – there are so many different types of insulins & new oral medications that no doctors can keep up!
  • Prescribe short-acting or mixed (combined) insulin with meals rather than set times
  • Patients (particularly the elderly) may have more relaxed targets for hyperglycaemia given the danger hypoglycaemia poses
  • Consider prescribing the hypoglycaemia protocol for patients on insulin as it prevents delay – but ensure you write that a doctor should be called whenever it is needed
Non-opioid analgesia
  • Read more here
  • Be careful of paracetamol-containing prescriptions (“co-“) – it is easy for someone to subsequently prescribe paracetamol
  • Be careful of NSAIDs due to Upper GI bleeds & AKI.
    • Avoid them if possible, otherwise, prescribe them at the lowest effective dose for the shortest possible duration
    • Avoid in the elderly or those with impaired renal function
    • Sometimes colchicine is used instead (e.g. for pleurisy or gout/pseudogout) but start low as this can cause quite significant diarrhoea
    • Always look for other medications that might potentiate gastric bleeding: anticoagulants, SSRIs, steroids
    • Have a low threshold of giving a short course of proton-pump inhibitors alongside them
  • Read more here (& opiate dependence/withdrawal)
  • Ensure you review the renal & liver function considering oxycodone in patients with a reduced eGFR
  • Prescribe PRN laxatives & antiemetics
  • Consider PRN naloxone as it prevents delay in administration – but ensure you write that a doctor should be called whenever it is needed
  • When converting from one form to another – seek senior, pharmacy or pain team input. has a great calculator for conversions.
  • Don’t forget that for controlled drugs you must write it out in full & sign on discharge
  • For methadone, to avoid overdose always ensure it is checked by the pharmacist, drugs or substance misuse team. You cannot rely on patients as it could be dangerous.
  • Consider oxygen as a drug and prescribe target ranges to avoid type 2 respiratory failure
  • This also allows Early Warning Scores to be adjusted accordingly
Remember, making a mistake doesn’t make you a failure. Reflecting & learning from them is vital.

Further Reading & References

Written by Dr Akash Doshi (CT2)
Review & Edits by Dr Thomas Grant (FY3) & Ayesha Jain (Medical SpR)

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