Drug Interaction Report

GENERALLY AVOID: Theoretical concerns exist that chemotherapeutic agents and other bone marrow depressants may potentiate the myelosuppressive effects of samarium sm 153 lexidronam. In clinical trials, white blood cell and platelet counts decreased to a nadir of approximately 40% to 50% of baseline in 95% of patients within three to five weeks after administration of samarium sm 153 lexidronam, and tended to return to pretreatment levels by eight weeks. The potential for additive bone marrow toxicity with myelotoxic treatments including chemotherapy or external beam radiation has not been studied.

MANAGEMENT: The manufacturer recommends avoiding concomitant use of samarium sm 153 lexidronam with chemotherapy or external beam radiation therapy unless benefits are anticipated to outweigh the risks. Moreover, samarium sm 153 lexidronam should not be given after either of these treatments until there has been time for adequate marrow recovery. Caution and close monitoring of bone marrow function are advisable if coadministration with other myelotoxic agents is required. Patients should be advised to contact their physician if they develop signs and symptoms of myelosuppression such as pallor, dizziness, fatigue, lethargy, fainting, unusual bleeding or bruising, or signs of infection such as fever, chills, diarrhea, sore throat, muscle aches, shortness of breath, blood in phlegm, weight loss, red or inflamed skin, body sores, and pain or burning during urination.

GENERALLY AVOID: Grapefruit juice may significantly increase the plasma concentrations of olaparib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. In a drug interaction study with 57 patients, mean olaparib systemic exposure (AUC) was increased approximately 2.7-fold by the potent CYP450 3A4 inhibitor itraconazole. Simulations using physiologically-based pharmacokinetic (PBPK) models suggest that a moderate inhibitor (fluconazole) may increase the AUC of olaparib by 2.2-fold. The interaction has not been studied with grapefruit juice. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Increased exposure to olaparib may increase the risk of adverse effects such as hematologic toxicity, nausea, vomiting, diarrhea, anorexia, dyspepsia, and abdominal pain or discomfort.

MANAGEMENT: Food containing grapefruit, grapefruit juice, Seville orange (a citrus relative of the grapefruit), or Seville orange juice should be avoided during treatment with olaparib. Some authorities also recommend avoiding starfruit (carambola) and pomegranate.