Dear Mr Fiddaman,
Thank you for your email dated 24 July to the Department of Health expressing your view that patients should be tested for deficiency in CYP 2D6 before being treated with Selective Serotonin Reuptake Inhibitors (SSRIs). I have been asked to reply.
I understand that you have had correspondence with the Medicines and Healthcare products Regulatory Agency (MHRA) on this issue, and that you are aware of the conclusions of the Committee on Safety of Medicines' Expert Working Group on the Safety of SSRIs that a number of different factors, including genetic variation, could potentially impact the effectiveness and safety of SSRIs for individual patients.
Before a test for CYP 2D6 deficiency could be recommended for routine clinical use, there would need to be evidence from specific clinical trials which demonstrated the value of such a test in predicting which patients would suffer adverse reactions. Research of this nature has been very limited and we currently do not have good evidence to suggest that people who are CYP 2D6 deficient are at higher risk of adverse reactions to SSRIs. A recently published article on this subject - Pharmacogenetics of Selective Serotonin Reuptake Inhibitors and Associated Adverse Drug Reactions (Pharmacotherapy 2009;29(7):822-831) - has reviewed the available evidence for a genetic basis of adverse reactions to SSRIs. The review highlights the large number of genetic variations which could affect the response of the individual to SSRIs, and the authors conclude that ‘no clear associations have been established between CYP 2D6 and the risk of adverse reactions’.
It is important that patients are monitored for adverse effects of SSRIs, whatever the underlying reason is for them experiencing the adverse effects. There are warnings present in the product information in line with this. Where there is evidence that the effect of paroxetine on CYP 2D6 has clinically relevant impact on patient safety - in the area of interactions between paroxetine and other drugs - there are detailed warnings in the product information.
The impact of genetic variation is important for the effectiveness and safety of many drugs, but the science of pharmacogenetics still has limited application in clinical practice. The MHRA is working with other European regulatory authorities and the European Medicines Agency to identify where there are screening mechanisms available to identify patients who will gain the greatest benefit from a particular medicine, or who may have an increased risk of adverse reactions.
You may be interested to know that the Department recently awarded Liverpool University and Professor Munir Pirmohamed the first NHS Chair in Pharmacogenetics. Professor Pirmohamed leads a team of clinicians, scientists and nurses in identifying genetic variations that dictate a patient’s positive or negative response to a drug.
The Chair will complement a £10million Centre for Personalised Medicines created at Liverpool University . In addition to contributing to research on pharmacogenetics, the remit of the NHS Pharmacogenetics Chair includes helping to establish a UK Pharmacogenetics Forum.
The Department had previously targeted funding for pharmacogenetics, and funded six research projects at a cost of around £4million. The focus of the research is on existing medicines, the pharmacogenetics of which are unlikely to be addressed without public sector funding. This included research on certain generic medicines used in the NHS, such as warfarin, an anti-clotting drug used to treat thrombotic disorders, and drugs involved in epilepsy and hypothermia or drugs that have been implicated in toxicity.
I hope this is helpful.
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Department of Health
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