Why Pharmacogenetic Testing Matters in Clinical Practice

Pharmacogenetics Explained for Clinical Practitioners

Pharmacogenetics (PGx) is increasingly embedded in clinical pathways across cardiovascular disease, psychiatry, neurology and pain management. Aligning prescribing to a patient’s genetic metaboliser status can improve efficacy and reduce adverse drug reactions — a major contributor to hospital admissions and prolonged recovery.

In stroke management, CYP2C19 poor metabolisers are significantly less likely to benefit from clopidogrel. This is recognised by NICE, with genotype-guided antiplatelet therapy already adopted in several UK centres. Similarly, CYP2D6, CYP2C19 and CYP2B6 pathways underpin treatment success and tolerability for antidepressants, opioids and many other commonly used medicines.

At AttoDiagnostics, we provide UK-based, accredited PGx testing across more than 120 medications, helping prescribers achieve better patient outcomes with clearer clinical direction — especially when first-line therapy has not worked as expected.

Key Takeaways

• Helps select the right medication and dose based on CYP450 pathways (e.g., CYP2C19, CYP2D6, CYP2B6)
• Highest actionability where CPIC Level A / NICE-recognised drug-gene interactions exist
• UK Biobank data: >20% of statin users may benefit from genotype-guided prescribing
• Particularly valuable in stroke/TIA, psychiatry, cardiology, neurology, and pain
• Reduces trial-and-error prescribing, repeat consultations, and side effects

Example Clinical Scenarios

Hospital-Based: Secondary Prevention in Stroke

A 63-year-old TIA patient is discharged on clopidogrel. Follow-up reveals recurrent symptoms despite adherence. Genotyping confirms a CYP2C19 poor metaboliser phenotype. Switching therapy in line with NICE guidance reduces secondary event risk and prevents further deterioration.

Primary Care / Private Mental Health

A 42-year-old patient has trialled sertraline with limited improvement and significant side effects. PGx testing identifies CYP2B6 poor metaboliser and CYP2C19 poor metaboliser phenotypes. This predicts substantially higher sertraline exposure, increasing side-effect risk. The report recommends alternative antidepressants not reliant on these pathways. With a targeted switch, the patient gains faster symptom stabilisation and improved tolerability.

Pharmacogenetics: Frequently Asked Questions

What is pharmacogenetic testing?

A genetic assessment that shows how a patient metabolises and responds to specific medicines, informing safer, more effective prescribing.

Is pharmacogenetic testing available in the UK?

Yes — including via UKAS-accredited laboratories such as AttoDiagnostics, with clinician-ready reports and support.

Who should consider CYP2C19 testing for clopidogrel?

Stroke and cardiology patients where antiplatelet effectiveness is critical. NICE guidance now references CYP2C19 testing.

How does PGx support antidepressant prescribing?

CYP2D6/CYP2C19/CYP2B6 status predicts treatment success and tolerability in SSRIs, TCAs, SNRIs and other mental health medicines.

What does “poor” or “rapid” metaboliser mean?

Pharmacogenetic phenotypes describe how efficiently enzymes metabolise drugs. Poor metabolisers may accumulate drug and experience toxicity; rapid metabolisers may see reduced benefit.

How accurate are PGx results?

Genotyping is >99% analytically accurate for validated markers. Each drug-gene pair is assigned an evidence level indicating clinical actionability.

Which medications are covered?

• More than 120 widely prescribed drugs including...
• Cardiology – clopidogrel, simvastatin
• Mental health – sertraline, citalopram, amitriptyline, atomoxetine
• Pain – codeine, tramadol, morphine …and many more.

Does PGx replace clinical judgement?

No — it supports more informed decisions, especially where response is unpredictable or polypharmacy introduces risk.