MECHANISM OF ACTION
Carbamazepine, phenobarbital, and phenytoin may induce
the metabolism of ulipristal by CYP P-450-3A4.(1)
DISCUSSION
CYP P-450-3A4 inducers may decrease levels and effectiveness of
ulipristal. Enzyme induction may take 2-3 weeks to wear off. Plasma levels
of ulipristal may be reduced even if the CYP P-450-3A4 inducer was
discontinued in the previous 2-3 weeks.(1)
CLINICAL EFFECTS
Concurrent use or use of carbamazepine, phenobarbital, or
phenytoin within the previous 2-3 weeks may result in decreased levels and
effectiveness of ulipristal.(1)
SEVERITY LEVEL
2-Severe Interaction: Action is required to reduce the risk
of severe adverse interaction.
PATIENT MANAGEMENT
The UK manufacturer of ulipristal states that
concurrent use with CYP P-450-3A4 inducers such as carbamazepine,
phenobarbital, or phenytoin is not recommended. Decreased effectiveness of
ulipristal may occur even 2-3 weeks after discontinuation of these
agents.(1)
PREDISPOSING FACTORS
None determined.
REFERENCE