Drug Interaction Report

MONITOR: Coadministration with dabrafenib may decrease the plasma concentrations of drugs that are primarily metabolized by CYP450 3A4 and/or 2C9. Dabrafenib has been found in vitro to be an inducer of these isoenzymes. Onset of induction is likely to occur after 3 days of repeat dosing with dabrafenib; however, transient inhibition of CYP450 isoenzymes may be observed during the first few days of treatment. In 12 study subjects, administration of the CYP450 3A4 probe substrate midazolam following repeat doses of dabrafenib 150 mg twice daily for 15 days reduced midazolam peak plasma concentration (Cmax) by 61% and systemic exposure (AUC) by 74%. When a single 15 mg dose of warfarin was coadministered similarly with dabrafenib, the AUC of S(-) warfarin decreased by 37% and that of R(+) decreased by 33%. S(-) warfarin, the biologically more active enantiomer, is primarily metabolized by CYP450 2C9, while R(+) warfarin is a substrate of CYP450 3A4 and 1A2.

MANAGEMENT: Caution is advised when dabrafenib is prescribed with drugs that undergo metabolism by CYP450 3A4 and/or 2C9. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever dabrafenib is added to or withdrawn from therapy. Significantly reduced plasma concentrations and loss of efficacy may occur with sensitive substrates of CYP450 3A4 or 2C9 such as hormonal contraceptives, immunosuppressants (cyclosporine, everolimus, sirolimus, tacrolimus), ivacaftor, and warfarin-type anticoagulants. Alternatives to these medications should be considered if possible.

ADJUST DOSING INTERVAL: Administration of lomitapide with food may increase the risk of common gastrointestinal adverse reactions such as diarrhea, nausea, vomiting, dyspepsia, abdominal pain or discomfort, abdominal distension, constipation, and flatulence. Absorption of concomitant oral medications may be affected in patients who develop diarrhea or vomiting.

GENERALLY AVOID: Grapefruit juice may significantly increase the plasma concentrations of lomitapide. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Weak CYP450 3A4 inhibitors can increase lomitapide exposure (AUC) by approximately 2-fold according to the product labeling. Ketoconazole, a potent CYP450 3A4 inhibitor, has been shown to increase lomitapide AUC by 27-fold .

GENERALLY AVOID: Coadministration with alcohol may increase the risk of hepatotoxicity associated with the use of lomitapide. In a premarketing clinical trial, 34% (10/29) of patients treated with lomitapide had at least one elevation in alanine aminotransferase (ALT) or aspartate aminotransferase (AST) 3 times the upper limit of normal (ULN) or greater, and 14% (4/29) had at least one elevation in ALT or AST 5 times ULN or greater. There were no concomitant clinically meaningful elevations of total bilirubin, international normalized ratio (INR), or alkaline phosphatase. Lomitapide also increases hepatic fat, with or without concomitant increases in transaminases. In the same study, the median absolute increase in hepatic fat was 6% after both 26 and 78 weeks of treatment, from 1% at baseline, measured by magnetic resonance spectroscopy. Hepatic steatosis associated with lomitapide may be a risk factor for progressive liver disease, including steatohepatitis and cirrhosis. Clinical data suggest that hepatic fat accumulation is reversible after stopping treatment with lomitapide, although the long-term consequences are unknown.

MANAGEMENT: Lomitapide should be taken once daily with a glass of water, without food, at least 2 hours after the evening meal. Strict adherence to a low-fat diet (<20% of total calories from fat) and gradual dosage titration may also help to reduce gastrointestinal intolerance. Patients should avoid consumption of grapefruit, grapefruit juice, and any supplement containing grapefruit extract during treatment with lomitapide. Since alcohol may increase levels of hepatic fat and induce or exacerbate liver injury, the manufacturer recommends that patients taking lomitapide not consume more than one alcoholic drink per day.

ADJUST DOSING INTERVAL: Food may reduce as well as delay the absorption of dabrafenib. In study subjects, administration of dabrafenib with a high-fat meal decreased peak plasma concentration (Cmax) and systemic exposure (AUC) by 51% and 31%, respectively, and delayed median Tmax by approximately 3.6 hours compared to administration in the fasted state.

MANAGEMENT: Dabrafenib should be taken at least 1 hour before or 2 hours after a meal.