Mavacamten (Camzyos)
A heart medicine for obstructive hypertrophic cardiomyopathy. In people whose CYP2C19 barely works it takes about 23 days to fall by half instead of 6 to 9, yet the dose is set by regular heart scans, not by the gene.
What this drug connects to
The genes involved
Mavacamten (Camzyos) relaxes the over-squeezing heart muscle in obstructive hypertrophic cardiomyopathy. It is cleared mainly by CYP2C19, and in poor metabolisers, whose CYP2C19 barely works, the label reports the total amount in the body rose by 241% after one dose and took about 23 days to fall by half, against 6 to 9 days. Even so, the label gives no separate dose by genotype: everyone starts at 5 mg a day and the dose is set by regular heart scans, which is why those scans are required.
US prescribing information for CAMZYOS (mavacamten), revised September 2026: sections 2.1, 12.3 and 12.5. This is the label itself, not a CPIC guideline.
How common these versions are, by ancestry
The share of people who carry at least one copy of each version. For the same medicine, it often differs more than tenfold between groups.
CYP2C19 *2 rs4244285 — a non-working version of the enzyme
CYP2C19 *17 rs12248560 — a faster version of the enzyme
Worked out from each group's allele frequency: Korean from the Korean studies published in dbSNP, the rest from gnomAD's ancestry groups (via Ensembl), as the survey defines them, not races. How common a version is in a group says nothing about any one person; only a test does.
Questions about Mavacamten (Camzyos)
What is mavacamten?
Mavacamten, sold as Camzyos, is a capsule for symptomatic obstructive hypertrophic cardiomyopathy, a condition in which the heart muscle is too thick and squeezes too hard. It relaxes the muscle so blood can leave the heart more easily. In the US it is for adults and for children who weigh at least 30 kg.
What does CYP2C19 have to do with it?
CYP2C19 is the main liver enzyme that clears mavacamten. In poor metabolisers, whose CYP2C19 barely works, the label reports the total amount in the body rose by 241% after one dose, and the medicine took about 23 days to fall by half, against 6 to 9 days in normal metabolisers.
So is the dose set by my genotype?
No. The label gives no separate dose for poor metabolisers. Everyone starts at 5 mg a day, and the dose is moved between 2.5, 5, 10 and 15 mg by regular heart scans that measure how well the heart pumps and how blocked its outflow is. Genotype explains why two people on the same dose can end up so different, which is why the scans are required.
How common are CYP2C19 poor metabolisers?
According to the Camzyos label, about 2% of people of European ancestry, 4% of people of African ancestry, and about 13% of East Asians.
What is the boxed warning on Camzyos?
Heart failure. Because mavacamten weakens how hard the heart squeezes, too much of it can cause heart failure, and some other medicines can raise its level. In the US it is only available through a restricted programme called the CAMZYOS REMS.
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Mavacamten (Camzyos). MyGeneLog™. https://www.mygenelog.com/drugs/mavacamten