ST EMLYN’S · MLA REVISION GUIDE
Prescribing
01 / CHAPTER 10
Safe prescribing starts before the prescription
Prescribing combines a clinical decision with an instruction that another person must be able to understand and act on safely. Imagine being the pharmacist dispensing the medicine, the nurse administering it and the patient taking it at home. Each needs a clear account of what is intended. An apparently small error in a dose, route or instruction can have important consequences.
As a medical student, you should develop the knowledge and judgement to propose, calculate, check and explain a prescription. You cannot independently authorise a clinical prescription in your student role. On placement, agree how practice prescriptions will be reviewed and signed by an authorised prescriber; never use another person’s login or allow an exercise to be mistaken for a live order. Once qualified, work within your registration, competence and local supervision arrangements.
Prescribing is relevant to the AKT, clinical assessment and the work expected at graduation. The MLA itself has two components, the AKT and CPSA. The Prescribing Safety Assessment (PSA) is a separate assessment delivered by the British Pharmacological Society and MSC Assessment, with its own arrangements. Your school will explain its requirements and which resources are permitted in each assessment. Do not assume that access allowed in the PSA is allowed in every MLA task.
Prepare using the BNF, BNF for Children, current local formulary and relevant national guidance. Practise locating the indication, formulation, dose, cautions, contraindications, interactions, monitoring and patient advice. Finding the drug’s name is only the start of checking it. The GMC prescribing guidance explains the professional responsibilities that surround the prescription.
02 / CHAPTER 10
A systematic prescribing method
1. Define the problem and intended benefit
Identify what you are treating and what improvement you expect. Check whether a medicine is needed, whether the diagnosis or severity changes the choice and whether a non-drug approach would be more suitable. A prescription is not the automatic ending to every consultation. In a station, state the indication rather than simply choosing a familiar medicine from a list.
2. Check the person, not just the condition
Confirm identity, allergies and the nature of any previous reaction. Review age, relevant weight, pregnancy or breastfeeding, kidney and liver function, comorbidities and the ability to take the proposed formulation. Obtain a medicine history that includes prescribed, over-the-counter and complementary products, recent treatment and doses already taken. Ask how medicines are actually used; a repeat list may not describe current practice.
Consider practical factors such as swallowing, dexterity, cognition, language, access to medicines and support at home. For an older person taking several medicines, check whether a new symptom could be an adverse effect or interaction. For a child, use the correct age and weight-based source rather than treating the dose as a smaller version of an adult prescription.
3. Choose and check the medicine
Use a current source for this indication and patient group. Check the exact medicine and formulation, strength, dose, route, frequency, duration and maximum limits. Look for contraindications, cautions, interactions and adjustments. Do not assume that a modified-release product can be substituted for an immediate-release product, or that two liquid strengths are interchangeable.
When uncertain, identify the precise uncertainty and use the appropriate help: a pharmacist, supervising prescriber, specialist team or medicines-information service. “I have checked the usual dose, but renal impairment may change it” is a useful request. It allows the discussion to resolve a decision rather than simply transfer an unexamined task.
4. Write or enter a complete instruction
Use the correct patient record and prescribing section. Specify the product and formulation, dose, route, timing, duration or review date and any administration instructions. For an as-required medicine, include the indication, minimum interval and maximum permitted amount over the relevant period. For an infusion, include the solution, concentration where relevant, volume and rate. Complete the required authorisation and identification fields through the approved workflow.
Read the completed order as a whole. Check that the dose agrees with the strength selected and that a quantity, unit or frequency has not been placed in the wrong field. In an assessment, do the task actually requested: reviewing an existing chart requires you to identify and explain a problem, while writing an order requires a usable final instruction.
5. Explain, monitor and review
Explain the purpose, how to take or use the medicine, important adverse effects and what should prompt help. Check understanding in a way that tests your explanation: “Could you tell me how you will take this when you get home?” Agree how response and harm will be monitored, when treatment will be reviewed and who will act on the results. Document a change or stop decision as carefully as a new prescription.
The cycle continues after the prescription. A medicine may be ineffective, poorly tolerated or no longer needed. Review the reason for treatment and the patient’s experience rather than renewing it automatically. Use the GMC guidance and current BNF medicines-optimisation guidance alongside supervised clinical practice.
03 / CHAPTER 10
Outpatient and community prescribing
An FP10 is an NHS prescription form used in England for community dispensing, including appropriate outpatient prescribing. Other UK nations use their own forms and systems. Electronic prescriptions are common, but you must still understand the information that makes an instruction legal, unambiguous and clinically appropriate.
- Confirm the correct patient identifiers, including name and address, with date of birth and relevant clinical details. For prescription-only medicines, the age is legally required for children under 12; include a current weight when needed to check a child’s dose.
- Specify the medicine, formulation, strength, dose, route where relevant, frequency and quantity or intended duration. Make directions understandable to the person taking the medicine.
- Include the required prescriber details, date and valid signature or electronic authorisation. A printed name or scanned signature is not automatically a valid substitute for the required authorisation.
- Check whether additional controlled-drug or other legal requirements apply. Do not assume that every prescription has the same validity period.
Use the BNF prescription-writing guidance for the detailed requirements. Most ordinary prescriptions are valid for six months, whereas many controlled-drug prescriptions have a 28-day validity period. Validity for dispensing is different from the duration of treatment or the quantity to supply. See NHS prescription information and the BNF controlled-drug requirements for the applicable rules.
At discharge, reconcile the intended medicines with the admission list and explain what has changed and why. Make clear which medicines were started, stopped or adjusted, what supply has been provided and what monitoring or follow-up is needed. A patient and their GP should not have to infer the plan from a list of drug names.
04 / CHAPTER 10
Inpatient and electronic prescribing
Inpatient prescribing includes regular, one-off, as-required and time-critical medicines, infusions and medicines managed on separate charts or specialist systems. Check the active orders and administration record before adding treatment. A medicine may already have been given, withheld, stopped or prescribed elsewhere, so a clean-looking new entry can still duplicate a dose.
Electronic prescribing can support checking, but the prescriber remains responsible for the clinical decision and the final order. Confirm the patient, episode and selected medicine, including formulation and strength. Review default values, start times, duration and route. Read alerts in context and resolve an important interaction or allergy concern; do not assume either that every alert is irrelevant or that the absence of an alert proves safety.
When changing treatment, make the intended stop, hold or replacement explicit so both old and new orders are not administered unintentionally. Check how the system records a one-off dose and when the next regular dose will occur. For a time-critical medicine, communicate the plan to the team rather than assuming a saved order has already been given. Local induction should include downtime procedures and how to seek urgent pharmacy or prescribing support.
On paper, use the correct chart section, legible entries and the local process for signing, dating and amending an order. On either medium, record allergies accurately, include the indication where appropriate and arrange monitoring. These are substantive differences in workflow; inpatient prescribing is not simply an outpatient prescription with a time added. GMC prescribing guidance applies across settings and technologies.
05 / CHAPTER 10
Doses, units and calculation checks
Begin with the source instruction: is it a dose per administration, a total daily dose divided into administrations, a dose per kilogram or a rate? Establish the relevant patient weight and the maximum limit before calculating. Keep units visible at every step and check that the final amount can be measured with the available formulation and equipment. A numerically correct calculation can still use the wrong indication, weight or concentration.
- Write down the required amount and its units. Convert units deliberately before calculating.
- Calculate the dose using the applicable source, then apply any stated maximum or patient-specific adjustment.
- If a volume is needed, divide the required amount by the concentration expressed in matching units.
- Check the result independently for plausibility and practical measurement. Use the required independent check for high-risk treatment.
- Document and communicate the final dose clearly; show the method when an assessment asks for it.
Use a leading zero for a value below one and avoid an unnecessary trailing decimal zero. Write “micrograms”, “nanograms” and “units” in full. State liquid strength clearly and avoid an instruction that gives only a volume without making the product and intended dose clear. These conventions reduce the chance of a tenfold or thousandfold error; see BNF prescription writing.
Worked arithmetic, not a treatment recommendation
Suppose a calculation exercise explicitly states that a patient requires 12 mg of an unnamed medicine and supplies a solution containing 4 mg/mL. The volume is 12 mg ÷ 4 mg/mL = 3 mL. The milligram units cancel. This demonstrates the calculation only: it does not establish that 12 mg is a safe dose for any real medicine, patient or route.
For a course supplied as one tablet three times a day for seven days, the arithmetic is 1 × 3 × 7 = 21 tablets. Before using that quantity clinically, the medicine, strength, schedule and duration must already have been justified. Do not let a neat quantity calculation conceal an inappropriate prescription.
06 / CHAPTER 10
Intravenous fluids are a prescription
First decide why intravenous fluid is needed and whether oral or enteral intake can meet the need. NICE’s five Rs—resuscitation, routine maintenance, replacement, redistribution and reassessment—help distinguish different clinical problems. A maintenance prescription is not a resuscitation plan, and ongoing losses need their own assessment.
Assess fluid status, intake, losses, observations, weight where relevant, comorbidity and blood results. Specify the fluid, volume and rate, and make a monitoring and review plan. Reassess the response and watch for overload or persistent depletion. Older or frail patients and those with cardiac or kidney disease may need particular care. Use NICE CG174 and its adult fluid algorithms with the responsible clinician; it is an adult hospital guideline, not a paediatric dosing guide.
In a practice task, explain your goal before calculating a volume or choosing a bag. State what information is missing and what observations or tests will determine the next prescription. During a placement, propose and discuss the plan; a student’s calculation must not become an unauthorised fluid order.
07 / CHAPTER 10
Recognise abbreviations; write clear instructions
You will encounter the abbreviations below in records and teaching material. This is a recognition table, not a recommendation to use shorthand. Prefer clear English and the approved choices in the local prescribing system. If a direction is ambiguous, clarify it with the prescriber before it is acted on. The BNF recommends directions in English wherever possible.
| Abbreviation | Meaning you may encounter | Safer approach |
|---|---|---|
| PO / O | Oral; “O” is particularly unclear | Write oral or by mouth. |
| IV | Intravenous | Select or write the full route where possible. |
| IM | Intramuscular | Specify the intended route. |
| SC | Subcutaneous | Avoid any unclear handwriting or route abbreviation. |
| PR / PV | Rectal / vaginal | Write the route in full to avoid confusion. |
| INH / NEB | Inhaled / nebulised | Specify the medicine and device or delivery method. |
| TOP | Topical | Specify site and application instructions. |
| OD | Often once daily; can have other meanings in eye care | Prefer “once daily”; clarify ambiguity rather than guessing. |
| OM / mane | In the morning | Write the timing in words. |
| ON / nocte | At night | Write the timing in words. |
| BD / TDS / QDS | Twice / three times / four times daily | Use clear English and specify intervals when these matter. |
| X-hourly | At intervals of X hours | State the actual interval, not a variable. |
| PRN | As required | Add indication, minimum interval and maximum amount. |
| Stat | Immediately, as a one-off dose | Use the one-off section and check previous administration. |
An “as required” order is incomplete if the person administering it cannot tell when, why or how often to give it. Similarly, “as directed” does not communicate a plan to someone who has never received those directions. Be particularly careful when a medicine is used at different doses or intervals for different indications.
08 / CHAPTER 10
Review the original prescription example
The historical FP10 illustration is retained below as a prescription-review exercise, not as a model prescription to copy. It shows co-amoxiclav, a one-week instruction and a quantity of 21 “capsules”. Read the issues alongside the image; the original artwork has not been altered.
- Formulation: the current product cited here is a 500 mg/125 mg tablet. The image’s “capsules” wording does not match that formulation. Specify the actual product correctly.
- Clinical context: the image does not establish an indication, allergy history or renal function. You cannot approve the medicine or its duration from the form alone.
- Instructions: use clear English for the frequency and an unambiguous formulation and route. Check the required identifiers and prescriber authorisation in the real workflow.
- Quantity: 21 units follows the illustrated three-times-daily, seven-day arithmetic, but that does not validate the clinical decision.
The current co-amoxiclav 500 mg/125 mg tablet product information includes three-times-daily use for specified adult and larger-child contexts, with patient-specific cautions and renal adjustment. It does not justify a universal seven-day course. Select an antimicrobial and duration using the actual infection, patient and current guidance.
Open the historical FP10 illustration and review it
09 / CHAPTER 10
Practise the whole prescribing task
Use a varied set of cases: an adult in the community, a child needing a weight-based calculation, an older inpatient with several medicines, a pregnant patient and someone with impaired kidney function. For each, explain the indication, perform the checks, produce the instruction and describe monitoring and patient advice. Then review a deliberately flawed prescription and explain both the error and how to correct it.
Use an approved training system, practice chart or clearly labelled educational exercise. Ask a pharmacist or supervising clinician to review your reasoning as well as the final entry. If you make a mistake, identify whether it arose from knowledge, interpretation, calculation, selection or communication and practise that step again.
- BNF: medicine information, interactions and prescribing guidance
- BNF for Children: paediatric medicine information
- SCRIPT: safer prescribing e-learning
- Official Prescribing Safety Assessment information and practice access
- NICE CG174: intravenous fluids in adults
- GMC: good practice in prescribing and managing medicines
If a possible prescribing error occurs in clinical care, tell the responsible clinician promptly, protect the patient from further harm and help establish what was prescribed and what was actually given. Follow the local reporting and candour process. Pharmacists and other team members are valuable partners in identifying and resolving problems; seek their expertise with a clear clinical question.