Drug Interactions between taletrectinib and thioguanine

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of taletrectinib. The proposed mechanism for the interaction is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice but has been reported for other CYP450 3A4 inhibitors. In a clinical study, taletrectinib peak plasma concentration (Cmax) increased by 1.8-fold and systemic exposure (AUC) increased by 3.3-fold following concomitant administration of itraconazole, a potent CYP450 3A inhibitor. According to the product labeling, administration of taletrectinib with a moderate CYP450 3A inhibitor is predicted to increase taletrectinib Cmax and AUC by up to 1.5- and 2.6-fold, respectively. Increased exposure to taletrectinib may increase the risk and/or severity of adverse effects such as hepatotoxicity with liver enzyme elevations, lung toxicities, QT prolongation, hyperuricemia, myalgia with creatine phosphokinase elevation, and skeletal fractures.

ADJUST DOSING INTERVAL: Coadministration with high-fat food (1000 calories, 50% fat) increased taletrectinib Cmax and AUC by 1.5-fold, and the predicted increase in the QTc interval is 20.5 msec.

MANAGEMENT: The manufacturer recommends avoiding food or drink containing grapefruit during treatment with taletrectinib. In addition, taletrectinib should be administered on an empty stomach at about the same time each day, at least 2 hours before or 2 hours after food intake.

MONITOR: The concomitant or sequential use of other agents known to induce hepatotoxicity may potentiate the risk of liver injury associated with thioguanine. A high risk of liver toxicity characterized by vascular endothelial damage has been reported with long-term continuous use of thioguanine, particularly in children receiving the drug as part of maintenance therapy for acute lymphoblastic leukemia and in other conditions associated with continuous use. Liver toxicity usually presents as the clinical syndrome of hepatic veno-occlusive disease (hyperbilirubinemia, tender hepatomegaly, weight gain due to fluid retention, and ascites) or with signs of portal hypertension (splenomegaly, thrombocytopenia, and esophageal varices). Histopathological features include hepatoportal sclerosis, nodular regenerative hyperplasia, peliosis hepatitis, and periportal fibrosis.

MANAGEMENT: The risk of hepatic injury should be considered when thioguanine is used with other potentially hepatotoxic agents (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; nucleoside reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice). 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. Baseline and regular monitoring of hepatic function is recommended. Thioguanine therapy should be discontinued if there is evidence of toxic hepatitis or biliary stasis, as reversal of signs and symptoms of liver toxicity have been reported upon withdrawal. Early indications of liver toxicity are signs associated with portal hypertension such as thrombocytopenia out of proportion with neutropenia and splenomegaly. Elevations of liver enzymes have also been reported, but do not always occur.