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Drug Monitoring · PSA section guide

Drug Monitoring in the PSA: what it tests, how it is marked, and a real question

Know what to measure for a given medicine, when to take the sample, and what the result should change.

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8items in the exam
2marks each
16 / 200of the paper
92questions in the bank

At a glance

Items in the exam8
Marks per item2
Share of the paper16 of 200
Question styleSingle best answer from five
Primary skillKnowing what to measure, when, and what to do with it
BNF useMonitoring requirements in the monograph
PassthePSA bank92 questions, rated easy to hard
On PassthePSASingle best answer in the exam's layout
Time at exam pace1 min 12 s

What this section is really testing

  • Which parameter a drug needs monitored: renal function, liver enzymes, blood counts, electrolytes, a drug level, or a clinical sign.
  • Which kind of monitoring the situation calls for: a baseline before starting, a scheduled check, a test triggered by a symptom, or a timed level.
  • When to sample, especially for drug levels that are only interpretable at a defined time after the dose.
  • What the result changes: continue, adjust, hold, or stop.

A repeatable approach

  1. Identify the drug and its riskWhat organ or system does this drug threaten, or what narrow range must it stay in?
  2. Classify the monitoringBaseline, scheduled, symptom-triggered, or a timed drug level. The question usually fits one.
  3. Find the timingThe monograph's monitoring requirements state when. For levels, the relationship to the dose is the whole point.
  4. Interpret the resultAgainst the stated target or threshold, not against the general reference range alone.
  5. Decide the actionContinue, reduce, hold, stop, or re-sample. The BNF often states the trigger.

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BNF strategy for this section

The exam is open book, and the time is short. Know which heading answers which question before you open the monograph.

Drug→Monitoring requirements→Baseline / scheduled / triggered / level→Timing→Result→Action
What needs checking on this drug?
Monitoring requirements
When is the level taken?
Monitoring requirements, and the dose section for timing
What is the target range?
The monograph, and the treatment summary for the condition
The result is abnormal, now what?
Monitoring requirements and side-effects; dose adjustment under renal impairment where relevant

The general technique, with drills, is in the BNF speed guide.

Four kinds of monitoring

BaselineBefore starting: the value you will compare against.
ScheduledRoutine checks at defined intervals while on the drug.
TriggeredA new symptom or sign demands a test now.
Drug levelA concentration taken at a defined time relative to the dose.

A PSA item usually fits one of the four, and the wrong answers are often the right test from a different category: a scheduled test offered when the symptom needs a triggered one, or a random level when a trough was required.

Timing is the mark

For drug levels the relationship to the dose is the whole question. A trough is drawn just before the next dose; a peak at a stated interval after it. A level with no time is not a level.

Common traps

Right test, wrong timeA level drawn at the wrong point after the dose is uninterpretable, however correct the test.
Repeating what is already knownThe test that answered the question last week is not the one that matters now.
Confusing the four kindsA symptom demands a triggered test now, not the next scheduled one.
Reference range as targetFor narrow-margin drugs the therapeutic range, not the lab's normal range, decides the action.
Monitoring the wrong organKnow which system each high-risk drug threatens: kidney, liver, marrow, thyroid, electrolytes.

Areas worth being comfortable with

Not predictions. These are the broad clinical areas this section draws on, taken from the shape of the exam and the BNF; being fluent in them makes the lookup fast.

  • Narrow therapeutic index drugs: lithium, digoxin, gentamicin, vancomycin, theophylline
  • Warfarin and INR
  • Methotrexate, azathioprine and other immunosuppressants
  • Amiodarone: thyroid, liver, lungs
  • ACE inhibitors, diuretics and renal function
  • Statins and liver enzymes
  • Antipsychotics and metabolic monitoring
  • Antiepileptics
  • Biologics and infection screening
  • Steroids: glucose and bone

A real drug monitoring question from the bank

This is one of the 20 items every visitor can try free, in the interface the exam uses. Work it before you open the answer.

ID : TDM-18Drug Monitoring2 markseasy
Case presentation

A 45-year-old woman attends the gastroenterology clinic for review of the maintenance treatment for her inflammatory bowel disease, which has been in remission for a year. She reports no sore throat, fever, mouth ulcers or unusual bruising.

PMH: Crohn's disease.

DH: azathioprine 100 mg PO daily.

SH: non-smoker.

On examination: temperature 36.7°C, HR 74/min regular, BP 120/74 mmHg; abdomen soft and non-tender.

Investigations: TPMT activity normal before starting; last Hb 128 g/L (115–165), WCC 5.6 ×10⁹/L (4.0–11.0), platelets 240 ×10⁹/L (150–400). Regular blood monitoring is required while treatment continues.

QuestionSelect the test most important to monitor regularly because of a serious haematological risk.
(mark it with a tick)
MONITORING OPTIONS
  • full blood count and differential
  • serum calcium and phosphate
  • thiopurine methyltransferase activity
  • thyroid function tests and cortisol
  • vitamin B12 and folate levels
Answer and marking
Correct answer

full blood count and differential

Marks

2

Explanation

Azathioprine can cause bone marrow suppression, so the full blood count is monitored (and thiopurine methyltransferase activity is checked before starting). Allopurinol markedly increases azathioprine toxicity.

Try another drug monitoring question →

More free drug monitoring questions, each with its full explanation

TDM-88 · HardAn 84-year-old on apixaban reviewed after four days of vomiting and diarrhoea2 marks →

Before you submit

  • Which of the four kinds of monitoring is this?
  • Is the timing right relative to the dose?
  • Am I judging against the drug's target, not the lab's range?
  • Does the result actually change management?
  • Is the action aimed at the drug, not the number?

Practice questions

92 Drug Monitoring questions, easy to hard, marked like the exam

Every answer comes with the explanation and the BNF reference behind it. Twenty questions across all eight sections are free. Pass guarantee: fail after 400+ questions and your access is extended free for 3 months.

Practise this section →Try the free 20-question sample

Continue revising

Data InterpretationActing on results: continue, adjust, hold or stop2 marks per item →Adverse Drug ReactionsAttributing a presentation to a medicine2 marks per item →Prescription ReviewFinding the culprit drug in a realistic chart4 marks per item →

View all 8 sections and the exam overview →

Section weightings follow the published PSA blueprint. The BNF headings named here are the current online BNF's. Check any dose or threshold against the BNF before you rely on it; this page teaches the method, the BNF holds the numbers.

Practise Drug Monitoring →