Drug Interaction Report

Coadministration with niraparib may decrease the plasma concentrations of drugs that are substrates of the CYP450 1A2 isoenzyme. At high concentrations, niraparib is able to weakly induce CYP450 1A2. If niraparib is used in combination with substrates of CYP450 1A2, particularly those with a narrow therapeutic range (e.g., clozapine, theophylline, ropinirole), then monitoring for signs and symptoms of reduced exposure to the CYP450 1A2 substrate should be considered.

The effect of grapefruit juice on the pharmacologic activity of caffeine is controversial. One report suggests that grapefruit juice increases the effect of caffeine. The proposed mechanism is inhibition of cytochrome P-450 metabolism of caffeine. However, a well-conducted pharmacokinetic/pharmacodynamic study did not demonstrate this effect. The clinical significance of this potential interaction is unknown.