Drug Interaction Report

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.

MONITOR: The risk of neurotoxicity may be increased when local anesthetics are used together with intraspinal ketamine. Animal and cell studies have shown that the combined neurotoxicity of lidocaine and ketamine are additive.

MANAGEMENT: Caution is advised during concomitant use of local anesthetics with intraspinal ketamine.

GENERALLY AVOID: Coadministration with pexidartinib may decrease the plasma concentrations and therapeutic effects of drugs that are substrates of CYP450 3A4. The proposed mechanism is increased clearance due to pexidartinib-mediated induction of CYP450 3A4 isoenzyme. Coadministration with pexidartinib (400 mg twice daily) decreased the total systemic exposure (AUC 0-INF) and peak plasma concentration (Cmax) of midazolam (a sensitive CYP450 3A4 substrate) by 59% and 28%, respectively.

MANAGEMENT: Concomitant administration of pexidartinib with drugs that are substrates of CYP450 3A4 should generally be avoided, particularly those with a narrow therapeutic range. The potential for diminished therapeutic effects should be considered when pexidartinib is prescribed in combination with drugs that are substrates of CYP450 3A4. Dosage adjustments as well as clinical and laboratory monitoring of the CYP450 3A4 substrate drug should be considered whenever pexidartinib is added to or withdrawn from therapy with these drugs.

ADJUST DOSING INTERVAL: The presence of food may increase the absorption and toxicity of pexidartinib. Administration of pexidartinib with a high-fat meal increased peak plasma concentration (Cmax) and systemic exposure (AUC) by 100% and prolonged the time to reach peak plasma concentration (Tmax) by 2.5 hours.

GENERALLY AVOID: Grapefruit or grapefruit juice may increase the plasma concentration and risk of adverse effects of pexidartinib, including potentially fatal hepatotoxicity. The mechanism is inhibition of CYP450 3A4-mediated metabolism of pexidartinib by certain compounds present in grapefruits. Concomitant administration of itraconazole, a strong CYP450 3A4 inhibitor, increased pexidartinib peak plasma concentration (Cmax) and systemic exposure (AUC) by 48% and 70%, respectively.

MANAGEMENT: Pexidartinib should be administered on an empty stomach, at least one hour before or two hours after a meal or snack. Consumption of grapefruit or grapefruit juice should generally be avoided during pexidartinib therapy. If concomitant use is unavoidable, the dose of pexidartinib should be reduced according to the manufacturer's recommendations. If concomitant use of grapefruit or grapefruit juice is discontinued, the dose of pexidartinib may be increased (after 3 plasma half-lives of a strong CYP450 3A4 inhibitor) to the dose that was used prior to consumption of grapefruit or grapefruit juice.

MONITOR CLOSELY: Coadministration of ketamine with other central nervous system (CNS) depressants, including alcohol, may result in profound sedation, respiratory depression, coma, and death. In addition, opioid analgesics, barbiturates, and benzodiazepines may prolong the time to complete recovery from anesthesia.

MANAGEMENT: During concomitant use of ketamine with other CNS depressants, including alcohol, close monitoring of neurologic status and respiratory parameters, including respiratory rate and pulse oximetry, is recommended. Dosage adjustments should be considered according to the patient's clinical situation. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of ketamine. Use in combination may result in additive central nervous system (CNS) depression and/or impairment of judgment, thinking, and psychomotor skills.

GENERALLY AVOID: Coadministration of oral ketamine with grapefruit juice may significantly increase the plasma concentrations of S(+) ketamine, the dextrorotatory enantiomer of ketamine. The proposed mechanism 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. When a single 0.2 mg/kg dose of S(+) ketamine was administered orally on study day 5 with grapefruit juice (200 mL three times daily for 5 days) in 12 healthy volunteers, mean S(+) ketamine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 2.1- and 3.0-fold, respectively, compared to administration with water. In addition, the elimination half-life of S(+) ketamine increased by 24% with grapefruit juice, and the ratio of the main metabolite norketamine to ketamine was decreased by 57%. The pharmacodynamics of ketamine were also altered by grapefruit juice. Specifically, self-rated relaxation was decreased and performance in the digit symbol substitution test was increased with grapefruit juice, but other behavioral or analgesic effects were not affected.

MANAGEMENT: Patients receiving ketamine should not drink alcohol. Caution is advised when ketamine is used in patients with acute alcohol intoxication or a history of chronic alcoholism. Following anesthesia with ketamine, patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination, such as driving or operating hazardous machinery, for at least 24 hours and until they know how the medication affects them. Patients treated with oral ketamine should also avoid consumption of grapefruit and grapefruit juice during treatment. Otherwise, dosage reductions of oral ketamine should be considered.

GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.