Drug Interactions between hydroxypropyl chitosan / terbinafine topical and Pondimin

ADJUST DOSE: Coadministration with potent inhibitors of CYP450 1A2 or 2D6 may increase the plasma concentrations of fenfluramine. Over 75% of fenfluramine is metabolized to its major active metabolite, norfenfluramine, primarily by CYP450 1A2, 2B6 and 2D6. When a single 0.35 mg/kg dose of fenfluramine oral solution was coadministered with 50 mg once daily fluvoxamine (a potent CYP450 1A2 inhibitor) at steady state in healthy volunteers, fenfluramine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 22% and 102%, respectively, while the Cmax and AUC of norfenfluramine decreased by 44% and 22%, respectively. Coadministration with 30 mg once daily paroxetine (a potent CYP450 2D6 inhibitor) at steady state in healthy volunteers increased the Cmax and AUC of fenfluramine by 13% and 81%, respectively, and decreased Cmax and AUC of norfenfluramine by 29% and 13%, respectively. Elevated plasma levels of fenfluramine may increase the risk of serious adverse effects such as valvular heart disease, pulmonary arterial hypertension, blood pressure increases, and serotonin syndrome.

MANAGEMENT: When coadministered with a potent CYP450 1A2 or 2D6 inhibitor, the manufacturer recommends limiting fenfluramine to a maximum total daily dosage of 20 mg without concomitant stiripentol and 17 mg with concomitant stiripentol. If a potent CYP450 1A2 or 2D6 inhibitor is discontinued during maintenance treatment with fenfluramine, consider a gradual increase to the fenfluramine dosage normally recommended without inhibitors, but not to exceed the maximum daily dosage of fenfluramine specified in the product labeling.

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