The Prescribing Safety Assessment (PSA) is an online assessment of competency in the safe and effective prescribing of medications, taken by final-year medical students. This article explains how the PSA is structured and provides some useful tips for performing well on the exam.
There are 200 marks available over 120 minutes, these marks are split across 8 sections:
Prescribing – 8 x 10 marks
Prescription review – 8 x 4 marks
Planning management – 8 x 2 marks
Providing information – 6 x 2 marks
Calculation skills – 8 x 2 marks
Adverse drug reactions – 8 x 2 marks
Drug monitoring – 8 x 2 marks
Data interpretation – 6 x 2 marks
Questions will cover Medicine, Surgery, General Practice, Psychiatry, Paediatrics, Obstetrics & Gynaecology, and Geriatrics.
There are 36 seconds per mark; if you are struggling to find an answer within a suitable time frame for the available marks, make a best guess (there is no negative marking) and move on.
Get familiar with the BNF (both online and paper versions) and know where to find things as it isn’t always obvious or easy. For example, converting opioid doses is in the palliative care summary, HRT is in the sex hormones summary, and high INR management is in the oral anticoagulants summary.
The ‘Medicines Complete’ BNF is easier to navigate than NICE’s online BNF – you can access this via the PSA website
This section comprises 40% of the available marks. You will be given a clinical scenario and asked to prescribe one drug/ fluid. Each question has 4 marks available for drug choice, 4 marks for the dose, route and frequency, and 2 marks for signature and date/ time. There are often several correct drug/ dose/ route combinations which will receive full marks. Lower marks are given for suboptimal options.
Take care to sign and date all prescriptions correctly – it is a guaranteed 8% of the marks.
There will be 2 fluid prescribing questions – learn how much fluid a patient is likely to need for resuscitation, rehydration and maintenance, and which fluids to use.
For example, patients require ~ 1mmol/kg/day of K+, this should not be infused at a rate >10mmol/hr.
You will be given a clinical scenario and a list of 6-10 drugs the patient is taking, you will need to identify drugs that are contra-indicated (e.g. in renal impairment), causing the clinical picture (e.g. hypokalaemia, confusion, hypotension), or contain a dosing error.
The beginning of Appendix 1 in the paper BNF contains several tables of ‘drugs that cause…’. This saves you from looking up each drug individually when being asked which drug is most likely to cause ‘x’.
Control ‘F’ is very useful here.
Know which drugs are prescribed in MICROgrams (e.g. levothyroxine, digoxin) – these are often prescribed in MILLIgrams to catch you out.
The maximum dose of paracetamol is 1g QDS – common dosing errors will include 1g 4hrly or co-prescription of paracetamol and co-codamol.
Check the frequency drugs are prescribed at, methotrexate and some doses of bisphosphonates should be prescribed once weekly but may be prescribed daily to catch you out.
Learn common enzyme inducers/ inhibitors:
Enzyme inducers: PC BRAS – phenytoin, carbamazepine, barbiturates, rifampicin, alcohol (chronic excess) sulphonylureas. Others: topiramate, St John’s Wort, and smoking.
More than one drug may list the relevant ADR in its side-effect profile, note how common/rare the side-effect is and pick the drug for which the side-effect has the highest rate of occurrence.
You will be given a clinical scenario where a drug (often new) has been prescribed. You will be asked to select the most appropriate monitoring actions.
Read carefully whether you are being asked to assess that the treatment is working/ beneficial or whether you are assessing for adverse effects – you will do different tests for each of these.
Know what the best timing is for tests e.g. lithium levels.
Use a drug’s ‘monitoring requirements’ and ‘pre-treatment screening’ sections in the BNF.
You will be given a clinical scenario and investigation results. You will be expected to determine the most appropriate next step in management (which may be no change at all).
Be familiar with different dosing regimens for gentamicin, and how these are monitored.
Know how to use the treatment nomogram in paracetamol overdoses.
When titrating drugs, for example, thyroxine to get TSH in range, you should usually make the smallest increment change possible.
Be aware that abnormal test results don’t always alter the management plan – for example, serum transaminases can be raised by up to 3x the upper limit of normal before statins should be discontinued. [Ref: https://bnf.nice.org.uk/drug-class/statins.html]