Drug Interaction Report

GENERALLY AVOID: The use of azathioprine with other immunosuppressive or myelosuppressive agents may result in additive hematologic toxicities and increased risk of infections, particularly in transplant patients. Azathioprine alone may cause dose-related and potentially life-threatening bone marrow suppression, although it is usually reversible when managed promptly. Leucopenia, anemia, thrombocytopenia, and rarely, agranulocytosis, pancytopenia, and aplastic anemia have been reported. Dose-related reductions in numbers of circulating total white cells, granulocytes, and lymphocytes may also occur. Treatment with azathioprine alone or in combination with other immunosuppressants, particularly corticosteroids, has been associated with increased susceptibility to infections including severe or atypical infection and reactivation with varicella zoster virus, hepatitis B, cytomegalovirus, and other infectious agents. Very rare cases of JC virus-associated progressive multifocal leukoencephalopathy (PML), a severely disabling and potentially fatal opportunistic viral infection of the brain, have also been reported. In addition, chronic use of azathioprine with other immunosuppressants may increase the risk of lymphoma, skin cancer, and other malignancies. Again, the risk is greatest in transplant patients, with the exception of hepatosplenic T-cell lymphoma (HSTCL), which has occurred primarily in patients with Crohn's disease or ulcerative colitis, especially adolescent and young adult males.

MANAGEMENT: Concomitant use of azathioprine with other immunosuppressive or myelosuppressive agents should be avoided whenever possible. Close clinical and laboratory monitoring for hematologic toxicity is advised if coadministration is required. Since azathioprine is considered a slow-acting drug, delayed myelosuppression may occur, and effects may persist even after the drug has been discontinued. Prompt reduction in dosage or temporary withdrawal of azathioprine may be necessary if a persistently low or rapid decline in leucocyte count occurs, or if there is other evidence of bone marrow depression.

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.