Drug Interactions between macitentan / tadalafil and trabectedin

GENERALLY AVOID: Additive hypotensive effects may occur when phosphodiesterase-5 (PDE5) inhibitors such as tadalafil are used with alcohol, as both are mild systemic vasodilators. In clinical pharmacology studies, more subjects administered alcohol at a dose of 0.7 g/kg (equivalent to approximately 6 ounces of 80-proof vodka in an 80-kg male; consumed within 10 minutes in study subjects, providing blood alcohol levels of 0.08%) in combination with tadalafil 10 or 20 mg single doses had clinically significant decreases in blood pressure than with alcohol alone. There were reports of postural dizziness, and orthostatic hypotension was observed in some. When tadalafil 20 mg was administered with alcohol at a lower dose of 0.6 g/kg (equivalent to approximately 4 ounces of 80-proof vodka in an 80-kg male), orthostatic hypotension was not observed, dizziness occurred with similar frequency relative to alcohol alone, and the hypotensive effects of alcohol were not potentiated. Neither tadalafil nor alcohol affected the plasma concentrations of the other.

GENERALLY AVOID: Coadministration with grapefruit juice is likely to increase the plasma concentrations of tadalafil, which is primarily metabolized by CYP450 3A4. However, the interaction has not been studied. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit.

MANAGEMENT: Patients taking tadalafil should avoid consuming large amounts of alcohol (for example, 5 units or more), which may increase the potential for orthostatic signs and symptoms including increase in heart rate, decrease in standing blood pressure, dizziness, and headache. It may also be appropriate to avoid consuming large amounts of grapefruit juice.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of trabectedin. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit.

GENERALLY AVOID: Coadministration of trabectedin with other agents known to induce hepatotoxicity such as alcohol may potentiate the risk of liver injury. Reversible, acute increases in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) have occurred frequently in patients treated with trabectedin alone or with pegylated liposomal doxorubicin in clinical trials. In one U.S. trial with 378 patients, grade 3 or 4 elevated liver function tests (defined as elevations in ALT, AST, total bilirubin, or alkaline phosphatase) were reported in 35% of patients receiving trabectedin. ALT or AST elevations greater than eight times the upper limit of normal (ULN) occurred in 18% of patients, and drug-induced liver injury (defined as concurrent elevations in ALT or AST more than three times ULN, alkaline phosphatase less than two times ULN, and total bilirubin at least two times ULN) occurred in 1.3% of patients.

MANAGEMENT: Consumption of grapefruit or grapefruit juice during treatment with trabectedin should be avoided. Excessive use of alcohol is also not recommended. 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. Monitoring of alkaline phosphatase, bilirubin, AST, and ALT should occur regularly during trabectedin treatment in accordance with the product labeling, or as often as necessary when clinical symptoms develop. Trabectedin must not be used in patients with elevated bilirubin at the time of initiation of cycle. Elevated liver function tests should be managed with treatment interruption, dosage reduction, or permanent discontinuation depending on the severity and duration of abnormality.