🩺 Prescription Writing Principles

Prescription writing is a legal and clinical process that authorizes the dispensing or administration of medications. In the UK, this must adhere to strict GMC guidance and legal standards to ensure patient safety. A safe prescription involves choosing the correct drug, dose, route, and frequency for a specific patient, while carefully considering allergies, interactions, and contraindications. Use of the BNF and clear, unambiguous documentation (increasingly via EPMA) are the cornerstones of preventing medication errors and ensuring effective therapeutic outcomes.

Prescribing is indicated when a pharmacological intervention is required to treat a diagnosis, manage symptoms, or provide prophylaxis. It is also used to authorize the administration of fluids, blood products, and oxygen. Prescriptions are necessary to legally enable a pharmacist to dispense medication or a nurse to administer it. Every prescription is a legal instruction and must be reviewed regularly to ensure ongoing clinical necessity (medicines optimization).

There are no contraindications to the act of writing a prescription, but specific medications are contraindicated based on patient factors (e.g., NSAIDs in severe renal failure or beta-blockers in asthma). A prescription must not be written if the clinician is not competent to manage the drug or if the patient's identity cannot be verified. Prescribing for one's self or family members is strongly discouraged by the GMC and should only be done in extreme emergencies where no other doctor is available.

Prescribing requires the British National Formulary (BNF) or BNF for Children (available as a book or app) to verify indications and safety. A formal prescription medium is needed—this may be an FP10 (primary care), an inpatient drug chart (Kardex), or an Electronic Prescribing and Medicines Administration (EPMA) system. For controlled drugs, specific stationary or system requirements must be met to satisfy UK law (Misuse of Drugs Act 1971). A black ink pen is standard for paper-based charts to ensure photocopiability and permanence.

Start by identifying the patient using three identifiers and checking their allergy status. Select the correct section of the drug chart (e.g., regular, PRN, or anticoagulation). Write the drug name clearly in block capitals using its generic name. Specify the dose clearly, using standard units (mg, g) and avoiding trailing zeros (e.g., 5mg, not 5.0mg). State the route (e.g., PO, IV, SC) and the frequency/time of administration. For PRN meds, include the indication and maximum 24-hour dose. Sign each entry and include your contact details to allow for clarification from the nursing or pharmacy staff.

Answering 'is this prescription correct?' requires interpreting the clinical context alongside the BNF. A dose may be 'correct' for the drug but inappropriate for a patient with a low eGFR or elderly frailty. Interpretation also involves recognizing the difference between 'stat' (immediate), 'regular', and 'PRN' (as required) sections of a drug chart. The clinician must interpret whether the chosen drug interacts with existing medications or exacerbates co-morbidities. A safe prescription reflects a balance of therapeutic benefit against the risk of adverse effects.

Common errors include 'omission of details' such as the route, frequency, or the patient’s weight for pediatric/low-weight adults. Illegible handwriting remains a significant risk in paper-based systems, leading to dispensing errors. Using ambiguous abbreviations like 'U' for units or 'μg' written as 'ug' can lead to 10-fold dosing errors. Failing to cross-reference the allergy status is a critical safety failure. Incomplete 'PRN' (as required) instructions, such as omitting the maximum daily dose or the minimum interval between doses, are also frequent.

In an OSCE or the PSA, always check for 'Allergies' first and document them clearly (including the reaction type). Use block capitals for the drug name to ensure clarity. Always write 'micrograms' and 'nanograms' in full—never use 'μg' or 'ng'. For liquid medications, specify the concentration if necessary, but focus on the dose in mass (e.g., mg) rather than volume. Ensure 'PRN' medications have a clear indication (e.g., 'for pain'). Finally, always sign and print your name and include your GMC number and bleep.

The Prescribing Safety Assessment (PSA) is a mandatory hurdle for UK graduates, testing these principles. Students must know the legal requirements for a valid prescription: patient name, DOB, address (for FP10), date, drug name (generic), dose, route, frequency, and prescriber signature. In the UK, generic prescribing is the standard unless the drug has a narrow therapeutic index (e.g., lithium, certain anti-epileptics). For Controlled Drugs (CDs), the total quantity and dose must be written in both words and figures.