Drug Interactions between famotidine / ibuprofen and pexidartinib

GENERALLY AVOID: Serious cases of hepatotoxicity, some fatal, have occurred in patients treated with pexidartinib. Concomitant use of other potentially hepatotoxic agents may potentiate the risk of liver injury. The mechanism of hepatotoxicity is unknown, its occurrence cannot be predicted, and it is unknown whether liver injury occurs in the absence of increased transaminases. In one study, 5% of patients who received pexidartinib developed signs of serious liver injury (elevated serum transaminases greater than 3 times the upper limit of normal (ULN) and total bilirubin greater than 2 times ULN). In these patients, peak ALT ranged from 6 to 9 times ULN, peak total bilirubin ranged from 2.5 to 15 times ULN, and ALP was greater than 2 times ULN. Liver transaminases and total bilirubin improved to less than 2 times ULN in these patients 1 to 7 months after discontinuing pexidartinib.

MANAGEMENT: The use of pexidartinib with other potentially hepatotoxic agents should be avoided. Patients treated with pexidartinib should have liver function tests, including AST, ALT, total bilirubin, direct bilirubin, ALP, and gamma-glutamyl transferase (GGT), prior to initiation of pexidartinib, weekly for the first 8 weeks, every 2 weeks for the next month, and every 3 months thereafter. Pexidartinib therapy may require a dosage reduction, to be withheld, or permanently discontinued based on the severity of the hepatotoxicity. A recurrence of increased serum transaminases, bilirubin, or ALP may occur upon rechallenge with a reduced dose of pexidartinib. Liver function tests should be performed weekly for the first month after rechallenge. Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice.

ADJUST DOSING INTERVAL: Coadministration with acid-reducing agents may significantly decrease the bioavailability and therapeutic effects of pexidartinib. The proposed mechanism is a pH-dependent reduction in drug dissolution and/or absorption. Concomitant administration of esomeprazole, a proton pump inhibitor, decreased pexidartinib peak plasma concentration (Cmax) and systemic exposure (AUC) by 55% and 50%, respectively. The effect of coadministration with an H2-receptor antagonist or locally-acting antacids on pexidartinib pharmacokinetics is unknown.

MANAGEMENT: If acid-suppression therapy is required, pexidartinib should be administered at least 2 hours before or 10 hours after taking an H2-receptor antagonist or 2 hours before or 2 hours after taking a locally-acting antacid. Concomitant use of pexidartinib with proton pump inhibitors should be avoided.

H2 antagonists may alter the pharmacokinetic disposition of some nonsteroidal anti-inflammatory drugs (NSAIDs), resulting in increased or decreased plasma concentrations. Data have been varied, even for the same NSAID. The mechanism may involve inhibition of metabolism, changes in gastric pH resulting in altered absorption, and/or reduced urinary elimination of the affected NSAIDs. Statistically significant changes have been small and of limited clinical significance when interactions have been observed.