We are delighted to announce that the CERSI-PGx has published its latest PGx prescribing guideline. We have made recommendations for the optimisation of clozapine prescribing and the adequate therapeutic monitoring in people with ADAN. Clozapine is a medicine that can help people with schizophrenia when other medicines haven’t worked.
Everyone taking clozapine must have regular blood tests to check their number of white blood cells. This number can drop for some people, which could affect their ability to fight infections. Regular blood tests ensure that a person’s white blood cell count stays above the minimum threshold level. Otherwise, clozapine may have to be stopped.
ADAN is a condition caused by a difference in a gene called ACKR1. This can affect anyone, but particularly people with African or Middle Eastern ancestry. People with ADAN have naturally low numbers of white blood cells, but they can fight infections normally. If a person taking clozapine is found to have ADAN, they are monitored on a different scale with a lower minimum threshold level for white blood cells. This usually means they can continue taking clozapine. However, ADAN is not always detected. This means that people with undetected ADAN are often unable to take clozapine because their white blood cell level appears too low.
In the guideline, we explain how to test for the genetic difference that causes ADAN in people taking clozapine. It has been designed so that it can be used in the UK’s NHS. We recommend three eligibility criteria, including pre-emptive testing for all people starting clozapine, testing for people registered in the Central Non-Rechallenge Database and reactive testing following a below threshold blood result (defined as ‘amber’ or ‘red’). We recommend that people with the Duffy-null genotype should be monitored using revised WBC/ANC thresholds for ADAN.
Our thanks to our Chair Professor Elvira Bramon and the team at UCL, Dr Stephen Murtough and Oriella Stellakis and to all the experts who contributed to the development of this guideline. Special thanks go to the lived-experience colleagues from the Side-By-Side Network for their time and support in co-writing the plain language summary of this guideline.