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 

What is DPYD?

DPYD is a gene that produces an enzyme called DPD. The DPD enzyme helps the body to break down some types of chemotherapy. This includes the drugs capecitabine, 5-fluorouracil (5-FU) and tegafur.

 

The DPD enzyme stops the drug from building up in the body and causing side effects.

 

What is the DPYD test?

The DPYD test is a simple blood test. It is sometimes called a DPD test. The blood test checks for the gene changes that are most likely to cause low levels of the DPD enzyme.

 

People with low DPD enzyme levels can have serious side effects from capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy. These can be life-threatening.

 

We use this test to check your risk of low DPD enzyme levels before you start these types of chemotherapy.

 

Why are DPYD tests needed?

Around 1 in 20 people have a low level of the DPD enzyme. This does not usually cause problems. But people with low levels are at more risk of serious side effects from capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy. These side effects can include:

  • severe diarrhoea
  • feeling or being sick (vomiting)
  • a sore or inflamed mouth or gut
  • a reduced number of white blood cells in your blood, which can weaken your immune system and make you more likely to get infections

 

You can get more information about possible side effects of your chemotherapy from your chemotherapy information sheet or cancer team.

 

Who needs a DPYD test?

Everyone who is offered capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy will have a DPYD test before they start treatment.

 

What happens if I have low DPD enzyme levels?

Most people will have normal DPD levels. But if you have low levels, your clinical team will talk to you about ways they can reduce your risk of serious or life-threatening side effects. This may include having:

•             a lower dose of the chemotherapy to start with

•             a different type of chemotherapy

 

If you have side effects

You may get side effects from chemotherapy even if your DPD levels are normal, and even if you started on a lower dose. If you have any side effects, it is still important to tell your cancer team.

 

If you have any side effects from your treatment, always contact your cancer team on the 24-hour contact number you have been given. 

 

This resource was drafted by Rachel Palmer and Kate North, clinical pharmacists affiliated with the NHS South West Genomic Medicine Service Alliance (GMSA), and reviewed by pharmacists and nurses with expertise in oncology, and pharmacogenomics: Jessica Keen, Dharmisha Chauhan and Veronica Chorro-Mari, Emma Groves, and Aris Saoulidis (affiliated with the NHS North West GMSA, NHS North Thames GMSA, NHS North East and Yorkshire GMSA, and NHS East GMSA respectively), and Vicky Cuthill (affiliated with Macmillan). 

The resource was reviewed by patients and public and public involvement and engagement (PPIE) groups from across three GMSAs (South West, North West, and North Thames), before a final version was agreed upon.

We wish to thank all of the patient and public stakeholders 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: DPYP Patient Information June 2024