Clobazam (Onfi)
A seizure medicine added to others for Lennox-Gastaut syndrome. In people whose CYP2C19 barely works, its active form reaches about 3 to 5 times the usual level, so the label starts them lower and goes slower.
What this drug connects to
The genes involved
Clobazam (Onfi), added to other treatment for Lennox-Gastaut syndrome, is turned into an active form that CYP2C19 clears. In poor metabolisers, whose CYP2C19 barely works, its US label says that form reaches about 3 to 5 times the usual level, so it starts them at 5 mg a day and raises the dose slowly to half the usual steps, considering the full maximum only from day 21.
US prescribing information for ONFI (clobazam), revised March 2024, sections 2.5 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 Clobazam (Onfi)
What is clobazam?
Clobazam, sold as Onfi, is a benzodiazepine seizure medicine. In the US it is added to other treatment for seizures in Lennox-Gastaut syndrome, a severe childhood epilepsy, from the age of 2.
What does CYP2C19 have to do with it?
The body turns clobazam into an active form, and CYP2C19 is what clears that form. In poor metabolisers, whose CYP2C19 barely works, the label says the active form reaches about 3 to 5 times the level seen in others.
What does the label say for poor metabolisers?
Start at 5 mg a day and raise the dose slowly, by weight, to half the doses in the usual schedule. From day 21, going up to the full maximum, 20 or 40 mg a day depending on weight, may be considered.
What is the boxed warning?
It is about taking it with opioids, about misuse and addiction, and about dependence and withdrawal, as with other benzodiazepines. It is not about genes. Clobazam should never be stopped suddenly without the prescriber.
Quoting this page
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Clobazam (Onfi). MyGeneLog™. https://www.mygenelog.com/drugs/clobazam