Personalised Drug Dosing Based on Genetics
What Is Personalised Drug Dosing?
Personalised drug dosing is an approach to selecting or adjusting a medicine’s dose according to an individual’s clinical characteristics, treatment needs and, where relevant, genetic information. The aim is to support safer, more informed prescribing by recognising that people can respond differently to the same dose of a medicine. This approach may involve pharmacogenomics, which explores how genetic differences can influence responses to medicines.
Genetic differences can influence how the body processes certain medicines, including how quickly a drug is broken down or converted into its active form. For some medicines, pharmacogenomic testing can identify variants that may help clinicians determine whether a standard starting dose, a lower or higher dose, or an alternative treatment should be considered.
However, genetics is only one part of personalised drug dosing. Clinicians also consider factors such as age, body weight, kidney and liver function, other medicines, existing health conditions and relevant clinical guidelines. Genetic results do not determine the correct dose on their own, and testing is useful only when the findings can inform a recognised clinical decision.
At London Genetics, the focus is on helping individuals and healthcare professionals understand when genetic information may support medication dosing decisions. The relevance of testing depends on the medicine being considered, the available evidence and the individual’s clinical circumstances.
How Can Genetics Influence Personalised Drug Dosing?
Genetic differences can affect how the body absorbs, activates, breaks down or eliminates certain medicines. These differences may influence how long a drug remains in the body, how much active medicine is available and the likelihood of dose-related side effects. Personalised drug dosing uses relevant genetic information, alongside clinical factors, to help guide prescribing decisions when supported by evidence.
Pharmacogenomic testing can identify variations in genes involved in drug metabolism or transport, as well as genes that influence how the body responds to particular medicines. Depending on the medicine and the genetic result, a clinician may consider adjusting the starting dose, choosing an alternative medicine or arranging closer monitoring.
For example, variations in the CYP2D6 gene can affect the metabolism of certain medicines, while TPMT and NUDT15 variants can influence the risk of toxicity from thiopurine medicines. These examples illustrate why genetic information may be relevant to dosing, although the appropriate action depends on the specific medicine and established prescribing guidance.
Genetic results do not provide a complete picture of how someone will respond to treatment. Age, organ function, other medicines, health conditions and clinical response remain important. Genetic testing is most useful when reliable evidence and prescribing guidelines show how a result can inform a practical dosing decision.
Which Factors Affect Personalised Drug Dosing Decisions?
Personalised drug dosing depends on more than genetic test results. Clinicians consider how a medicine is processed by the body, the individual's health and other factors that may influence its effectiveness, safety and appropriate dose.
| Factor | How It Influences Dosing |
|---|---|
| Genetic Variants | Variants in genes involved in drug metabolism or response may indicate whether a standard dose, a dose adjustment or an alternative medicine should be considered for certain treatments. |
| Age and Body Weight | Age-related changes and body weight can affect dose requirements, depending on the medicine and the individual's circumstances. |
| Kidney and Liver Function | Reduced kidney or liver function may affect how a medicine is cleared from the body, potentially requiring a different dose or closer monitoring. |
| Other Medicines | Drug interactions can change medicine concentrations or effects, influencing the need for dose adjustments or alternative treatment options. |
| Medical History and Existing Conditions | Current health conditions, previous adverse reactions and relevant medical history can affect treatment choices and prescribing precautions. |
| Clinical Guidelines and Treatment Response | Evidence-based prescribing guidance, treatment goals, observed response and, where appropriate, drug-level monitoring help clinicians determine whether a dose should be maintained or adjusted. |
Personalised drug dosing combines genetic evidence with clinical judgement. Genetic information can help guide dosing for selected medicines, but the final decision should account for the individual's overall health, the medicine being prescribed and relevant clinical guidance. A genetic result should not be used in isolation to change a prescribed dose.
How Does Genetic Testing Support Personalised Drug Dosing?
Pharmacogenomic testing can identify genetic variants that influence how the body processes or responds to certain medicines. When supported by clinical evidence, these findings can help healthcare professionals make more informed dosing decisions.
Review the Medication
- Identify the medicine being considered and the relevant prescribing decision.
- Check whether pharmacogenomic testing is recommended or supported by evidence for that medicine.
Analyse Relevant Genetic Variants
- A suitable biological sample is analysed by a laboratory using an appropriate genetic test.
- The analysis looks for variants in genes known to influence the processing or effects of specific medicines.
Interpret the Results
- Genetic findings are interpreted in relation to the medicine and relevant clinical guidelines.
- The results may indicate whether a standard dose, a dose adjustment or an alternative medicine should be considered.
Inform the Dosing Decision
- A qualified healthcare professional considers the genetic findings alongside medical history, organ function, other medicines and treatment goals.
- Where appropriate, the findings can help guide initial prescribing, dose adjustment or additional monitoring.
Genetic testing supports clinical decisions; it does not prescribe a dose on its own. Its usefulness depends on the medicine, the variants assessed and the available evidence. Any change to a prescribed dose should be made with the responsible healthcare professional.
Which Medicines May Require Personalised Drug Dosing?
Genetic information can help guide dosing for certain medicines when specific genetic variants are known to affect drug metabolism, treatment response or toxicity risk. The relevance of testing depends on the medicine, the patient's circumstances and current clinical guidelines.
| Medicine | Relevant Gene | Potential Dosing Implication |
|---|---|---|
| Warfarin | CYP2C9 and VKORC1 | Genetic information may help estimate an initial dose, alongside clinical factors and INR monitoring. |
| Abacavir | HLA-B | HLA-B*57:01 testing helps identify patients who should not receive abacavir because of the risk of a potentially serious hypersensitivity reaction. This primarily informs medicine selection rather than dose adjustment. |
| Certain antidepressants | CYP2D6 and CYP2C19 | Results may support consideration of dose adjustment or an alternative medicine for selected antidepressants, depending on the specific gene–drug guidance. |
| Thiopurines, such as azathioprine and mercaptopurine | TPMT and NUDT15 | Certain variants can increase the risk of severe bone marrow toxicity. Results may guide a lower starting dose or an alternative treatment, according to clinical guidance. |
| Fluorouracil and capecitabine | DPYD | Relevant DPYD variants can indicate an increased risk of severe toxicity and may inform starting-dose reduction or selection of an alternative treatment. |
Not every medicine requires genetic testing, and not every genetic result leads to a dose change. Testing is most useful when a well-established gene–drug relationship can inform prescribing. Depending on the medicine, results may guide dose selection, closer monitoring or the choice of treatment. Decisions should follow current clinical guidance and be made by the responsible healthcare professional.
Who May Benefit from Personalised Drug Dosing?
Personalised drug dosing may be relevant for people who are starting a medicine or reviewing an existing treatment when genetic differences are known to influence drug metabolism, dose requirements or the risk of adverse effects. Its value depends on the specific medicine, the available evidence and the individual’s clinical circumstances.
Genetic information may be particularly useful for people who:
- Are about to start certain medicines: Pharmacogenomic testing may help guide initial dosing when recommended by clinical guidelines.
- Have experienced unexpected side effects: Genetic findings may help explain some medicine-related reactions and inform future prescribing, although not all adverse effects have a genetic cause.
- Have had a limited treatment response: For selected medicines, genetic differences may contribute to how the drug is processed or activated.
- Take medicines with established gene–drug interactions: Testing may help clinicians identify variants that affect dosing, safety precautions or medicine selection.
- Need a review of their current medication: Existing genetic results may provide useful information when a clinician reassesses treatment, provided the findings are relevant to the medicines being considered.
Personalised drug dosing is not necessary for everyone, and genetic testing is not routinely useful for every medicine. Clinicians should consider whether a validated test can answer a relevant prescribing question and whether the result could change clinical management.
At London Genetics, the aim is to help individuals understand whether pharmacogenomic information may be relevant to their medication, including through medication compatibility testing, where appropriate, and what the findings could mean for clinical discussions. Any dosing changes should be assessed and authorised by the healthcare professional responsible for treatment.
How Are Genetic Results Used to Guide Drug Dosing?
Genetic test results can help clinicians determine whether genetic differences may affect how a person processes or responds to a particular medicine. When supported by clinical evidence, these findings can inform dosing decisions alongside other relevant health factors.
Identify Relevant Genetic Variants
Laboratory analysis identifies relevant variants in genes associated with drug metabolism, transport or response.
Interpret the Findings
Results are assessed in relation to the specific medicine, established gene–drug guidance and the potential clinical implications.
Consider Individual Health Factors
Clinicians consider genetic findings alongside age, kidney and liver function, other medicines, medical history and treatment goals.
Inform Dosing Decisions
Depending on the medicine and evidence, results may support a standard dose, a dose adjustment or consideration of an alternative medicine.
Plan Appropriate Monitoring
Genetic findings may help clinicians identify when additional monitoring or specific prescribing precautions should be considered.
What Are the Benefits and Limitations of Personalised Drug Dosing?
Personalised drug dosing can help clinicians use genetic information to guide prescribing for selected medicines. However, its usefulness depends on the strength of the evidence, the medicine involved and the individual's wider clinical circumstances.
| Potential Benefits | Limitations and Considerations |
|---|---|
|
More informed dose selection Relevant genetic findings may help clinicians choose an appropriate starting dose for certain medicines. |
Not applicable to every medicine Clinically useful gene–drug relationships have been established for specific medicines, not all treatments. |
|
Better-informed safety decisions Some genetic variants indicate an increased risk of dose-related toxicity or adverse drug reactions. |
Risk cannot be predicted completely Genetic findings cannot identify every potential side effect or guarantee that a medicine will be safe. |
|
Support for treatment selection Results may help clinicians consider a dose adjustment or an alternative medicine when supported by clinical guidance. |
Other factors remain important Age, organ function, other medicines, medical history and treatment goals can influence prescribing decisions. |
|
More targeted monitoring Genetic information may help identify patients who need specific precautions or closer clinical monitoring. |
Testing has defined limits Results depend on the genes and variants assessed, the test's scope and the quality of the available evidence. |
|
Useful information for future prescribing Relevant results may inform later prescribing decisions when the same gene–drug relationship applies. |
Clinical interpretation is essential Results must be interpreted in context and may not change treatment. Genetic findings alone do not determine the correct dose or guarantee treatment effectiveness. |
Personalised drug dosing can support more informed prescribing, but it does not replace clinical judgement. Genetic testing is most valuable when the results can guide a recognised clinical decision. A healthcare professional should interpret the findings alongside other relevant factors before recommending any medication or dosage change.
What Should You Consider Before Personalised Drug Dosing?
Before considering personalised drug dosing, it is important to establish whether genetic testing is relevant to the medicine being prescribed and whether the results could inform a clinical decision. Pharmacogenomic testing is most useful when reliable evidence connects specific genetic variants with drug metabolism, dosing or treatment safety.
Several factors can help determine whether testing is appropriate:
- Medicine-specific evidence: Check whether established clinical guidelines support pharmacogenomic testing for the medicine in question.
- Purpose of testing: Clarify whether the aim is to inform an initial dose, assess a potential risk of adverse effects, support treatment selection or guide future prescribing.
- Test coverage: Confirm which genes and variants are analysed. A test may not detect every genetic factor that influences a medicine’s effects.
- Clinical context: Genetic findings must be considered alongside age, kidney and liver function, other medicines, medical history and treatment goals.
- Interpretation of results: Results should be reviewed by an appropriately qualified healthcare professional who can explain their relevance and limitations.
- Timing and practicalities: Consider whether results will be available in time to inform treatment, as well as the test’s cost, availability and any follow-up requirements.
- Privacy and data handling: Understand how genetic information is stored, accessed and protected by the testing provider.
It is also important to understand that genetic testing cannot predict every side effect or guarantee that a medicine will work. Some results may not change the recommended treatment, while other prescribing factors may be more influential in a particular case.
Do not stop taking a medicine or change its dose based on genetic information without consulting your prescribing healthcare professional. The decision to test and any subsequent treatment changes should be guided by clinical evidence and your individual circumstances.
Frequently Asked Questions About Personalised Drug Dosing
What is personalised drug dosing based on genetics?
Personalised drug dosing uses genetic information alongside clinical factors to help guide the dose of certain medicines. Pharmacogenomic testing can identify genetic variants that influence how the body processes or responds to specific drugs.
Can genetic testing determine the correct dose of a medicine?
Not on its own. Genetic results can support dose selection for certain medicines, but healthcare professionals must also consider age, kidney and liver function, other medicines and clinical guidelines.
Which genes can influence drug dosing?
Genes such as CYP2D6, CYP2C19, CYP2C9, TPMT, NUDT15 and DPYD can influence the metabolism or safety of particular medicines. The relevant genes depend on the medicine being considered.
Can personalised drug dosing reduce the risk of side effects?
For selected medicines, genetic information can help identify an increased risk of certain adverse reactions and inform dose adjustments or alternative treatments. However, testing cannot prevent every side effect or guarantee that treatment will be safe.
Should I have pharmacogenomic testing before starting a new medicine?
Testing may be appropriate when established evidence or prescribing guidelines support its use for the medicine in question. It is not routinely necessary before every new prescription, so discuss its potential value with your healthcare professional.
Can genetic testing explain why a medicine has not worked for me?
Sometimes. Genetic differences can affect how certain medicines are metabolised or activated, which may contribute to treatment response. However, many other factors influence effectiveness, and genetic testing may not explain every unsuccessful treatment.
Will my genetic results be useful for future prescriptions?
Potentially. Relevant pharmacogenomic findings may inform future prescribing when the same gene–drug relationship applies. Their usefulness depends on the medicine, the scope of the test and current clinical guidance.
Who should interpret my pharmacogenomic results?
An appropriately qualified healthcare professional should interpret the results in the context of your medication, medical history and clinical needs. Any decision to change a prescribed medicine or dose should be made with the professional responsible for your care.
Does personalised drug dosing replace regular medical monitoring?
No. Genetic information complements rather than replaces clinical assessment, routine monitoring and follow-up. Depending on the medicine, blood tests, drug-level measurements or monitoring for adverse effects may still be necessary.
Discuss Personalised Drug Dosing with Our Genetics Team
Genetic information can help guide dosing decisions for certain medicines, but its relevance depends on the medication, the available evidence, and individual health factors. Discussing your circumstances with a genetics professional can help you understand whether pharmacogenomic testing may be useful.
How Can We Help?
Understand the Relevance of Testing: Explore whether genetic testing may provide useful information for a specific medicine or prescribing decision.
Understand Your Genetic Results: Learn how relevant genetic variants may influence drug metabolism, potential side effects, or dosing recommendations for selected medicines.
Explore Appropriate Next Steps: Understand the potential implications and limitations of testing, including how genetic findings may be considered alongside your medical history and other clinical factors.
A Personalised Approach to Pharmacogenomics
At London Genetics, we recognise that genetic results are only one part of informed prescribing. Their interpretation depends on the medicine involved, established clinical guidance, and individual circumstances.
Our aim is to help you understand how pharmacogenomic information may contribute to treatment decisions and whether further assessment could be appropriate.
If you are considering personalised drug dosing or would like to understand whether pharmacogenomic testing may be relevant to your medication, arrange a consultation to discuss your options.
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