Pharmacy — Referral to GP for a Drug Interaction with Warfarin
A community pharmacist refers a 64-year-old woman to her GP after identifying that the amoxicillin-clavulanate newly prescribed for a dental infection is likely to significantly increase her warfarin INR, raising her bleeding risk. The referral must present the clinical concern clearly and suggest a monitoring action without exceeding the pharmacist's scope.
Letter type
Referral
Write to
General Practitioner
Target length
180–200 words
The case notes
Patient: Mrs Grace Okonkwo, 64 years old; regular customer
Warfarin history: On warfarin 4 mg daily for AF; INR well-controlled at 2.3 (last tested 10 days ago); target 2.0–3.0; knows anticoagulation clinic contact
New prescription: Co-amoxiclav 625 mg TDS for 7 days — prescribed today by a locum dentist for an infected tooth; patient brings both prescriptions to pharmacy together
Concern: Amoxicillin-clavulanate is a known warfarin potentiator — antibiotic disrupts gut flora, reduces vitamin K synthesis, increases INR; significant interaction documented
Current INR: Last INR 2.3 (10 days ago); no INR booked during the antibiotic course
Symptoms: No current bleeding symptoms; dental pain managed with paracetamol
Patient informed: Explained the interaction to Mrs Okonkwo; advised not to add extra vitamin K foods or change diet; asked to watch for bruising or bleeding
Task: Write a referral letter to the GP, Dr Sarah McAllister, alerting her to the drug interaction and requesting that an INR check be arranged during the antibiotic course.
Writing task
Write a referral letter to the GP, Dr Sarah McAllister, alerting her to the drug interaction and requesting that an INR check be arranged during the antibiotic course.
What to include, what to cut
The hardest mark to win is selection. The same case notes contain decision-relevant facts and distractors. Here is what an examiner expects to see in a Grade B letter for this scenario, and what should be left out.
Include
-
The specific interaction: amoxicillin-clavulanate potentiates warfarin and will likely raise the INR
This is the pharmacist's clinical contribution — the GP may not have been alerted to the interaction by the dental prescriber. The mechanism (gut flora disruption) is worth a brief mention because it frames the urgency and the monitoring needed.
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The last INR and that no check is currently booked during the course
The gap in monitoring is the specific safety risk the GP must address. A well-controlled INR at 2.3 can swing into a dangerous range within days of starting the antibiotic.
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The specific request: an INR check mid-course or earlier if symptoms develop
A referral letter must request a concrete, time-specific action. 'Check INR at approximately day 3–4 of the course' is actionable; 'monitor appropriately' is not.
Leave out
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The dental history and the reason for the antibiotic
Context only — the GP does not need the dental history to act on the interaction. One line suffices: 'co-amoxiclav 625 mg TDS prescribed by dental practitioner for dental infection'.
-
The diet advice given to the patient
You gave this advice yourself; it does not change the GP's action. A brief mention that the patient has been counselled is enough; the content of your patient education belongs in the dispensing record.
Criterion in focus · Genre & Style
A pharmacist's referral to a GP is collegial and precise. The pharmacist is reporting a clinical observation to a prescribing colleague and requesting a specific action — neither deferential nor directive. 'I would appreciate it if you could arrange an INR check during the antibiotic course' is the correct register. 'I request that you' is too commanding; 'could you please perhaps consider' is too deferential.
Now write the letter — and find out what is blocking your Grade B
Write a 180–200 words referral letter from these notes, paste it into the free checker for an instant read, then submit it for a human grade against all six criteria. Dr Mariam's team returns line-by-line feedback, from $12.