Mavacamten is used to treat symptomatic obstructive hypertrophic cardiomyopathy (HCM). It is sold under the brand name Camzyos ® .

Patient information: CYP2C19 testing to guide Mavacamten dosing

This has been designed to provide information for patients who may undergo CYP2C19 genotyping prior to the prescription of Mavacamten.

Information for patients

In Hypertrophic Obstructive Cardiomyopathy (HOCM), the heart walls stiffen and the muscle thickens, which makes it difficult for the heart to pump blood through the body.

Mavacamten is a medicine that can help some patients who suffer from symptoms of HOCM. It does this by relaxing the heart muscles so that blood can be pumped more easily through the body.

The body has natural ways of breaking down this medication and some of this is controlled by the DNA that forms your genetic code. Some people have common DNA changes in a gene called CYP2C19 that mean they will break this medicine down more slowly. They may be at risk of having high levels of the medicine and then having the heart relax too much, which can cause heart failure.  These CYP2C19 changes have no impact on the body other than how it handles medicine. 

For this reason, to prevent heart failure from occurring, everyone who is prescribed Mavacamten in the UK should have a genetic test first to see if they have these common CYP2C19 changes. If they do have these DNA changes, they will be given a lower dose of the medication to prevent this side effect from occurring. This genetic testing may be done by routine blood test or saliva sample.

Some medications can interact with Mavacamten. If you start any of these medications, you should be sure to tell your doctor so that the dose of Mavacamten can be adjusted if necessary. This is particularly important for patients with the DNA variants as described above. Some examples of interacting medications are given in this leaflet.

Additionally, other commonly prescribed medications are broken down or activated by the body in the same way. Therefore, it is important to keep the results of this test to share with prescribers.

This resource was drafted by Dr Emma Magavern, a clinical pharmacologist affiliated with Queen Mary University of London, and reviewed by clinical geneticists and clinical pharmacology experts in pharmacogenomics: Dr John McDermott, Prof William Newman and Prof Mark Caufield (affiliated with the Manchester University NHS Foundation Trust and Queen Mary University of London and Barts Health NHS Trust respectively).

The resource was reviewed by public stakeholders from Cardiac Risk in the Young (CRY) before a final version was agreed upon. We wish to thank the CRY team and members for their valuable input.  All factual information included in this resource was correct at the point of publication but should be reviewed by the responsible healthcare professional if disseminated. 


Download in PDF format here: Patient Facing Information: CYP2C19 testing to guide Mavacamten dosing