01Principles and purposeThe professional or clinical skill and the decisions it supports.
Writing a prescription is the final translation of a clinical decision into an instruction that other people and systems must execute. The instruction crosses boundaries: a prescriber selects treatment, a pharmacist supplies a product, a nurse or patient administers it, and another clinician later reviews its effect. Each person sees a different part of the story. The prescription should carry the information needed to preserve the original decision across those boundaries. Ambiguity is therefore a clinical risk, not merely untidy documentation. A missing route, unclear formulation or absent end date can change what the patient actually receives even when the prescriber had the correct intention.
A useful approach separates clinical validity from instruction quality, then checks that they agree. Clinical validity asks whether the medicine is indicated, suitable and correctly dosed for this individual. Instruction quality asks whether the authorised treatment can be carried out without interpretation. An electronic system may enforce some fields while automatically populating others from an old order; a paper chart may make an omission visible but expose handwriting problems. Neither format supplies clinical judgment. The final check should focus on consequential assumptions, particularly imported doses, unusual units, time-critical medicines, high-risk formulations and prescriptions transferred from another setting.
Key points
- Check the patient, indication, allergy history and relevant organ function before writing the medicine order; a perfectly formatted prescription can still be clinically wrong.
- Specify medicine, formulation, strength when needed, dose, route, frequency and duration or review date. Add a maximum dose and indication to an as-needed instruction.
- Use a leading zero for a dose below one, avoid unnecessary trailing zeros, and write micrograms and units in full where abbreviation could create a dangerous misreading.
- For a suitable adult COPD exacerbation in which amoxicillin is selected, NICE NG114 gives 500 mg orally three times daily for 5 days; fifteen 500 mg capsules supply that course when no doses have already been given.
- Calculate supply from the actual formulation and remaining course, not merely from the number of days written on the label. Reconcile doses already administered before discharge.
- For infusions, state the medicine dose, diluent, final concentration or final volume, administration time or rate and required monitoring. A volume without its concentration does not define a dose.
- Before signing, read the prescription as the dispenser, administering nurse and patient would. Resolve any field that requires them to guess the intended treatment.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Determine whether the request concerns a new treatment, continuation, a one-off dose, an as-needed medicine, an infusion or a discharge supply. These orders need different time information. A request to rewrite an existing medicine is still a prescribing decision when the dose, route or clinical circumstances have changed.
Use the required identifiers and confirm that the clinical record belongs to the person being treated. Check the documented indication, age, current weight when relevant, pregnancy considerations and kidney or liver status. If another clinician proposes the drug, obtain enough information to take responsibility for the prescription rather than assuming their request removes the need for review.
Ask what happened, which medicine was involved and when the reaction occurred. A blank allergy box is not the same as a confirmed absence of known allergies. Distinguish a serious immediate allergy from an intolerance while ensuring that any unresolved high-risk history is assessed before prescribing a related medicine.
Modified-release tablets, liquids, patches, inhalers and injections are not interchangeable merely because they contain the same active ingredient. Strength can describe amount per tablet, per millilitre or per actuation. Determine the actual product required and whether a brand is necessary for a clinically important formulation or device distinction.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Current medicine and administration history - Why
- Identify duplicate treatment, recent doses and relevant interactions.
- Interpretation and limitations
- Review actual administrations as well as active orders, especially after ambulance or emergency treatment. A new inpatient chart can omit a dose already given elsewhere. Include non-prescription medicines when they share an active ingredient or change the safety of the proposed regimen.
- 02
Dose-relevant clinical measurements - Why
- Supply the patient factors needed for accurate medicine selection.
- Interpretation and limitations
- Confirm weight units and measurement date for weight-based treatment, and use a renal estimate appropriate to the medicine. A copied weight from several years earlier is a weak basis for a high-risk calculation. Check whether an acute change makes a previously acceptable dose unsuitable.
- 03
A current indication-specific reference - Why
- Verify the selected regimen and distinguish guideline from product details.
- Interpretation and limitations
- National guidance may specify a treatment course while a product source supplies formulation, renal restrictions and administration details. Check that the indication, age group and route match the patient. A search result giving a dose for another infection cannot establish the correct duration here.
- 04
The completed order and supply calculation - Why
- Test whether the prescription can be executed consistently.
- Interpretation and limitations
- Calculate units per dose, doses per day and days remaining. Verify the result by reversing the calculation against the intended course. For an electronic prescription, inspect the signed or previewed order rather than assuming that every selected value was retained correctly by the interface.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked exampleWrite an oral antibiotic course completelyAlex Morgan, date of birth 12 May 1962, training identifier LAB001, has a COPD exacerbation for which amoxicillin has been selected. No known drug allergy is confirmed; renal function is stable and normal, swallowing is safe, and no antibiotic doses have yet been given. Available capsules contain 500 mg.+
- 1Confirm the selection against the supplied diagnosis and safety information, then use the NICE NG114 adult regimen of amoxicillin 500 mg orally three times daily for 5 days. The clinical decision is a finite course, so an indefinite repeat order would not describe it.
- 2Convert dose to formulation units: 500 mg required divided by 500 mg per capsule equals 1 capsule each dose. Calculate supply as 1 capsule × 3 doses per day × 5 days = 15 capsules; no previous administrations need to be subtracted.
- 3Write the final order with the supplied patient identifiers, prescribing date 7 September 2026, amoxicillin 500 mg capsules, dose 500 mg, oral route, three times daily for 5 days, quantity 15 and the COPD-exacerbation indication. Add the prescriber authentication required by the prescribing system.
- 4Independently verify that 15 capsules divided by 3 daily doses supplies 5 days, that the route is oral and the product is a capsule, and that no allergy or duplicate course is present. Give practical dose-spacing advice and a review plan if symptoms worsen or fail to improve.
02As-needed treatmentMake an intermittent instruction unambiguousA patient needs a medicine for intermittent symptoms rather than scheduled dosing.+
- 1Name the symptom and establish how severity or response determines use. Confirm whether a regular medicine or combination product already contains the same active ingredient, because the daily maximum must include all relevant exposure.
- 2Write the single dose, route, minimum interval and maximum allowed in the specified time period. If a dose range is appropriate, explain the circumstance for using each end so that the person administering it does not make an unsupported clinical choice.
- 3Add a duration or review point and observations that should trigger reassessment. Repeated need for rescue treatment may indicate that the underlying condition or regular regimen is inadequately managed, even when each individual dose is within its limit.
- 4Read the order with the person who will administer it and check that they can determine whether another dose is due. Ensure that the administration record makes cumulative exposure visible across shifts and across regular and as-needed sections.
03TransitionConvert inpatient treatment into a discharge prescriptionAn adult is leaving hospital with a changed or time-limited medicine regimen.+
- 1Reconcile the final inpatient plan against the pre-admission list, actual recent doses and the discharge diagnosis. Identify medicines intentionally stopped, changed or temporarily held, and retain their reasons in the handover.
- 2Calculate the remaining supply using the treatment start date and doses already received. State a calendar stop or review date when relative wording could be misunderstood, especially for loading phases, steroid reductions or an antibiotic course begun in hospital.
- 3Ensure that the prescribed formulation and equipment can be supplied and used at home. A patient accustomed to ward administration may need teaching, an oral syringe, a device or carer support before the discharge instruction becomes practical.
- 4Check that the patient, pharmacy and receiving prescriber see the same regimen and monitoring plan. Confirm who will act on pending results or future dose changes rather than leaving responsibility implicit in the discharge summary.
05Relevant medicines and safetySpecific regimens and precautions when the skill involves prescribing.
Amoxicillin: selected COPD-exacerbation course
For the suitable adult in the worked case, 500 mg by mouth three times per day over 5 days; one 500 mg capsule per dose gives a total supply of 15 capsules.Antibiotics are selected after clinical assessment, not for every exacerbation. Check penicillin allergy, recent treatment, interactions and renal impairment; severe infection or organ impairment may require a different regimen and assessment.
06Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- After issuing a new prescription, check whether the medicine was obtained and used as intended when clinical risk or complexity justifies contact. An accurate order cannot produce benefit if the chosen formulation is unavailable or the instructions are misunderstood.
- For time-limited treatment, review clinical response and apply the planned end date. A remaining packet or repeat-list entry is not an independent indication to prolong the course.
- When prescribing from an electronic template, review alerts and imported values in context. Resolve clinically important warnings and record the reason for a deliberate override; repeated exposure to low-value alerts must not turn every warning into background noise.
- At each subsequent review, compare the current prescription with what the patient actually takes. A change made verbally or on a discharge letter may not yet have reached every supply system, creating contradictory instructions.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Dose and strength answer different questions
A 250 mg tablet may be used to deliver a 500 mg dose, while a 500 mg capsule supplies the same dose as one unit. Writing only the strength leaves the intended number of units uncertain when the dose is not also specified.
Duration and quantity should corroborate each other
A quantity calculation provides an independent check on a finite course. If the total supply implies twice the intended duration, investigate the formulation or frequency before signing rather than assuming the pharmacy will infer the intended correction.
An imported order is still a new decision
Copying a previous prescription can preserve an old error or omit a new contraindication. Check which clinical facts changed since the original order, including organ function, indication and the treatment phase.
Clarity protects the next person
The best final read asks what a competent colleague could reasonably misunderstand. Correcting that ambiguity before the order enters the supply chain is usually easier than reconstructing the intended instruction after an incorrect dose has been given.
08Common pitfallsFrequent interpretation and management errors.
- 01
Writing an as-needed dose without a minimum interval or total daily ceiling makes it difficult to decide whether another administration is safe.
- 02
Using a stock strength as if it were the prescribed dose can create an error when more than one tablet or a measured liquid volume is required.
- 03
Copying a hospital start date incorrectly can make a community prescription restart an antibiotic course that is already partly completed.
- 04
Signing an order with an unresolved allergy history transfers a clinically important uncertainty to the person administering the medicine.