AI Prescription Writer

Medical Prescription Writing: The Complete Clinical Guide

How to write safe, accurate prescriptions — dosing, drug interactions, renal adjustments, legal requirements and prescribing best practice for doctors and medical students

💊 What Is a Prescription 📋 Legal Elements ⚖️ Dosing & Adjustments ⚠️ Drug Interactions ❌ Prescribing Errors

What Is a Medical Prescription?

A medical prescription is a formal written instruction from a licensed prescriber to a pharmacist, authorising the dispensing of a specific medication to a named patient. It is a medicolegal document — errors in prescribing are one of the leading causes of preventable patient harm worldwide, responsible for an estimated 237 million medication errors annually in England alone (NHS England, 2023).

Prescribing rights vary by country and by professional registration. In the UK, independent prescribers include doctors, dentists, nurse prescribers, and pharmacist prescribers. In all cases, the prescriber carries full clinical and legal responsibility for every prescription they sign.

Legal Elements of a Valid Prescription

For a prescription to be legally valid and dispensable, it must contain all required elements. A pharmacist is legally obliged to reject any prescription missing these components.

Required Elements (BNF / WHO Standard)

Patient full name and date of birth
Patient address (for controlled drugs)
Date of prescribing
Drug name — generic preferred (INN)
Formulation (tablet, capsule, liquid, patch)
Strength / dose in unambiguous units

Route of administration
Frequency and timing
Duration or quantity to dispense
Special instructions (with food, at night)
Prescriber name, qualification, registration
Prescriber signature (handwritten or electronic)

Abbreviation	Latin	Meaning
OD	Omni die	Once daily
BD	Bis die	Twice daily
TDS	Ter die sumendum	Three times daily
QDS	Quater die sumendum	Four times daily
PRN	Pro re nata	As required
STAT	Statim	Immediately
AC / PC	Ante/Post cibum	Before/After food

Dosing, Renal & Hepatic Adjustments

Standard adult doses assume normal renal and hepatic function. Failure to adjust doses in organ impairment is a major cause of iatrogenic harm — particularly in elderly patients with CKD or liver disease who are already on multiple medications.

🫘 Renal Dose Adjustment

Use eGFR (CKD-EPI) not creatinine alone
Renally cleared drugs: antibiotics, digoxin, metformin, LMWH, NSAIDs
Metformin: stop if eGFR <30
Gentamicin: dose by levels, not schedule
NSAIDs: avoid in CKD 3b+
Always check BNF Appendix 3

🫀 Hepatic Dose Adjustment

Use Child-Pugh score to classify severity
Hepatically metabolised: opioids, statins, warfarin, benzodiazepines
Avoid NSAIDs in decompensated cirrhosis
Paracetamol: use with caution, reduce dose
Statins: avoid in active liver disease
Always check BNF Appendix 2

Paediatric Dosing

Always use weight-based dosing for children. Use the BNFc (British National Formulary for Children) or local formulary. Never extrapolate adult doses. Common formula: dose (mg) = dose per kg × weight (kg). Always double-check with a second prescriber or pharmacist.

Drug Interactions Every Prescriber Must Know

Drug interactions occur when one drug alters the effect of another — either increasing toxicity or reducing efficacy. With polypharmacy now common in elderly patients, checking for interactions before prescribing is essential.

Drug Combination	Risk	Action
Warfarin + NSAIDs	Major bleeding risk	Avoid — use paracetamol instead
ACEi + K-sparing diuretics	Hyperkalaemia → arrhythmia	Monitor K+ closely
SSRIs + Tramadol	Serotonin syndrome	Avoid combination
Metformin + Contrast dye	Lactic acidosis risk	Stop 48h before contrast
Statins + Macrolides	Myopathy / rhabdomyolysis	Temporary statin hold
Digoxin + Amiodarone	Digoxin toxicity	Halve digoxin dose, monitor levels

Common Prescribing Errors & How to Avoid Them

Prescribing errors account for up to 9% of all medication errors and are most common among junior doctors in the first year of practice. Awareness of common error patterns is the first step to prevention.

❌ Common Errors

Wrong dose or frequency
Allergy not checked before prescribing
No renal/hepatic dose adjustment
Unclear or ambiguous abbreviations
Drug interactions not checked
Decimal point errors (e.g. 1.0mg vs 10mg)
Using brand name only instead of generic

✅ Prevention Strategies

Always check allergy status first
Use BNF / BNFc for every unfamiliar drug
Check eGFR before renally cleared drugs
Write doses clearly — avoid trailing zeros
Use electronic prescribing where available
Ask pharmacist to review complex cases
Double-check high-risk drugs with colleague

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References

British National Formulary (BNF). NICE. Updated March 2026. bnf.nice.org.uk
NHS England. Medication Safety — Prescribing Errors. Patient Safety Report 2023.
WHO. Medication Without Harm — Global Patient Safety Challenge. Geneva: WHO; 2017.
Dean B, Schachter M, Vincent C, Barber N. Causes of prescribing errors in hospital inpatients. Lancet. 2002;359(9315):1373-8.
GMC. Good practice in prescribing and managing medicines and devices. Updated 2021.
MHRA. Drug Safety Update. Renal impairment and prescribing. Updated 2024.

⚠️ Medical Disclaimer: Content on this page is for educational purposes only. All AI-generated prescriptions require review and authorisation by a qualified, licensed prescriber before dispensing or administration.