High-risk drug monitoring in primary care: what to check

What high-risk drug monitoring means in primary care

High-risk drug monitoring is the routine safety work you run for patients on medicines with a narrow gap between benefit and harm: confirming they have current bloods, reading what those results actually show, and acting when something drifts. In a GP practice that mostly means DMARDs, lithium, amiodarone, anticoagulants and the renal function of anyone on an ACE inhibitor or a diuretic. Ordering the test is the easy part; the bulk of the work is spotting who is overdue and closing the loop safely before a quietly rising creatinine or falling neutrophil count becomes an admission.

Which medicines need blood tests, and why

Work backwards from what each drug can silently damage. The point of monitoring is to catch that harm while it is still a number on a screen.

DMARDs and methotrexate

These drugs suppress the bone marrow, the liver, or both, which is the whole reason for the bloods. For methotrexate you are watching the full blood count for cytopenias, the LFTs for hepatotoxicity, and U&Es because renal impairment raises the level. Two practical traps: methotrexate is once weekly, and the interactions training reference is worth a look because co-prescribing trimethoprim (another antifolate) can precipitate marrow suppression. The MHRA Drug Safety Update on methotrexate flags the risk of fatal overdose from inadvertent daily dosing, so the day of the week belongs on the prescription in full, not just "weekly".

Lithium monitoring

Few drugs you manage have a tighter therapeutic range. You are checking the level itself (a trough, taken the right number of hours post-dose, or the result is meaningless), plus renal function, thyroid function and calcium. It is also acutely sensitive to anything that reduces excretion, so a new NSAID, ACE inhibitor or diuretic, or a dehydrating illness, can tip a stable patient into toxicity. Check interactions before you touch anything else on the list.

Amiodarone monitoring

It accumulates in the thyroid and liver, so those are the two organs you watch. It can cause both hypo- and hyperthyroidism, so thyroid function is central, alongside LFTs. Its half-life is measured in weeks, which is the awkward bit: a thyroid or liver problem can surface, or persist, well after the drug is stopped. Treat "recently stopped amiodarone" as still on your monitoring radar.

Anticoagulants: warfarin and DOACs

Warfarin needs INR and a sensible eye on time in therapeutic range. DOACs are not INR-monitored, but they are far from fit-and-forget: renal function drives the dose, so at least annual renal function (check the current BNF and product SPC; more often in CKD or acute illness) tells you whether the dose is still right. A DOAC dose that suited a patient's kidneys two years ago may now be wrong.

ACE inhibitors, ARBs and diuretics

These are the highest-volume monitoring workload in most practices. You are checking U&Es for renal function, hyperkalaemia and, with diuretics, hyponatraemia, especially after a dose change or an intercurrent illness. This is where sick-day guidance earns its place.

High-risk drug monitoring frequency and shared care

The question you will be asked most is how often. Resist the urge to answer from memory. How often depends on the specific drug, how stable the patient is, and, above all, the local shared-care protocol. A newly started or recently dose-changed patient needs closer watching than someone who has been steady for years, and two neighbouring areas can legitimately specify different intervals for the same drug.

So the accurate answer is: check the current BNF entry, the SPS Medicines Monitoring tool (sps.nhs.uk/home/tools/drug-monitoring), and your practice's signed shared-care agreement for that drug. SPS is explicit that its Medicines Monitoring parameters are best-practice suggestions and that the final judgement rests with the prescriber for the individual patient. Where a specialist retains monitoring under shared care, know exactly where the responsibility boundary sits, because "I assumed the hospital was doing it" is how patients fall through the gap.

Finding and actioning overdue monitoring on the system

Theory only counts once you run the searches, chase the results and act on them. Build or use a saved search per drug group that flags active repeats with no in-date matching blood test, then work the list rather than waiting for reviews to surface people one at a time.

Take Mr Ali, 78, on methotrexate for rheumatoid arthritis plus ramipril and a thiazide. Your DMARD search flags him: his last full blood count sits well outside the window his shared-care agreement specifies. You recall him, the bloods come back with a creeping creatinine and a neutrophil count at the low end. This is where a monitoring task turns into a clinical decision. You would not simply re-authorise the repeat. You would hold the next methotrexate issue pending review, check for a new interacting drug or dehydrating illness, discuss with the patient, escalate to the GP or rheumatology per the shared-care route, and code the actions clearly. A borderline result you file without acting is worse than one you never ran.

This blends into the wider review: overdue monitoring is a standing prompt in a good structured medication review, and deprescribing decisions often lean on the STOPP/START criteria (version 3, 2023). If you want to drill the mechanics safely, the scored Practice Labs put you in front of real-feeling records where the monitoring is good, missed or unsafe, and the interactive STOPP/START reference and competency-mapped curriculum build the underpinning knowledge.

Frequently asked questions

Which medicines need regular blood test monitoring in primary care?

The common high-risk groups are DMARDs such as methotrexate, lithium, amiodarone, anticoagulants (INR for warfarin, renal function for DOACs), and ACE inhibitors, ARBs and diuretics for U&Es. Many are managed under shared care with a specialist. Always confirm the specifics against the current BNF and your local shared-care protocol.

How often should high-risk drugs be monitored?

There is no single interval. Frequency depends on the drug, how stable the patient is and the local shared-care agreement, which is why newly started or dose-changed patients are monitored more closely. Use the current BNF, the SPS Medicines Monitoring tool and your signed shared-care protocol rather than a remembered figure.

What should I do if monitoring is overdue?

Recall the patient and arrange the bloods before authorising further supply if the drug and result warrant it. If a result is abnormal, do not re-authorise automatically: withhold the next issue where appropriate, look for a cause such as a new interacting drug or acute illness, discuss with the patient, escalate per the shared-care route and code your actions.

Who is responsible for monitoring under a shared-care agreement?

The shared-care agreement itself defines who does what, and it varies by drug and area. Some monitoring stays with the specialist, some transfers to primary care once the patient is stable. Read the specific agreement rather than assuming, because unclear boundaries are a common cause of missed monitoring.

If you want to rehearse spotting and actioning overdue monitoring before it lands on a real patient, the Practice Labs are built for exactly that.