Anticipate before you prescribe — drug interactions and reconciliation

Station status

This is one MedVellum formative structured clinical encounter. The scoring, prompts and performance descriptions are educational feedback tools. They are not an official college station, timing, mark allocation, pass score or reproduced examination format. The encounter assesses interaction anticipation, enzyme-based reasoning, the choose-among-management-options decision, building a Best Possible Medication History, and a safe discharge reconciliation. [1] [7]

Candidate instructions

You are the paediatric registrar admitting Priya. Anticipate the interaction before you prescribe by naming the shared enzyme, the direction, and the timing. Choose among avoid, substitute, dose-adjust with monitoring, or accept with monitoring. Build a Best Possible Medication History from at least two sources. Reconcile at admission and discharge, and communicate the list in plain language. Say what you would assess or do; do not perform painful or distressing manoeuvres on the actor. [7]

Room setup and observable starting state

The encounter. Priya is 14, four years after liver transplantation, and is reviewed on the ward for oral candidiasis and a right lower-lobe pneumonia. Her long-term list includes twice-daily oral tacrolimus (levels in target range), sertraline, and a combined oral contraceptive. The on-call plan written at the end of the bed proposes oral fluconazole and oral clarithromycin. The candidate should recognise the predictable interaction before the prescription is signed and act on it. [1]

Simulation safety. The patient and parent are actors. Cards or the assessor supply vital signs, levels, and examination findings. No real drug is administered. [1]

Actor cues

Parent actor

• Begin with "She's had a rough week with the thrush and a cough." If asked about her usual medicines, answer: "She takes her transplant medicines twice a day, plus an antidepressant and the pill. I think she might take something herbal from the chemist too, but I'm not sure of the name." [7]

Child actor

• Answer briefly and accurately about your own medicines where you can; defer detailed history to the parent and the written record. Express mild anxiety about drug side effects if asked. [1]

Assessor cues and clinical data

Release findings as the candidate works through the prescription decision and the reconciliation. Reward anticipation before harm and penalise prescribing the interacting pair without an interaction check. [1]

The interaction check

The candidate must identify that tacrolimus is a CYP3A4 substrate with a narrow therapeutic window, and that both fluconazole and clarithromycin are potent CYP3A4 inhibitors. Expected strong behaviour: name the enzyme, predict a rapid rise in tacrolimus level with nephrotoxicity and neurotoxicity, avoid the combination, substitute nystatin for the candidiasis and azithromycin for the pneumonia, and arrange a level check if any azole is unavoidable. [1] [2]

Timing and direction

The candidate must state that inhibition acts within hours to days and causes toxicity, and contrast this with induction, which lowers substrate levels over one to two weeks. Expected strong behaviour: give both time courses when asked about the interaction, rather than only the inhibition answer. [1] [2]

The serotonergic and contraceptive layers

The candidate must consider that a macrolide adds QT risk to the SSRI, that tramadol must be avoided to prevent serotonin syndrome, and that rifampicin (not part of this regimen) would lower the contraceptive. Expected strong behaviour: demonstrate that every concurrent drug is a candidate substrate, and recognise polypharmacy as the combinatorial driver of risk. [6]

Building the Best Possible Medication History

The admission list was copied from the referral letter. Expected strong behaviour: refuse to accept a single source; build the BPMH from at least two sources including the family, the community pharmacy, and the GP; record name, dose, route, frequency, last dose, and adherence; and explicitly ask about over-the-counter and herbal products, anticipating that an unrecorded St John's wort would lower tacrolimus toward rejection. [7]

Discharge reconciliation

At discharge the regimen has changed. Expected strong behaviour: produce a verified, reconciled list explaining every change; communicate it in plain language and in writing; confirm it reaches the GP and community pharmacy; and set explicit tacrolimus monitoring review points with the transplant team. [10]

Marking domains

Debrief prompts

• Which interaction should have been anticipated before the prescription was signed, and which enzyme was shared? [1]
• How would the answer change if the new drug were rifampicin rather than an azole — what direction and what timing?
• Which sources would you use to build the Best Possible Medication History, and which unrecorded product could have caused harm here?
• How would you confirm the discharge list reached the GP and community pharmacy, and why does plain-language communication matter?