gefitinib, (Iressa discontinued in the US)

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is the dosage for gefitinib?

Gefitinib is taken by mouth. The dose is 250 mg once daily. The dose is the same for men or women of any age or weight, and gefitinib can be taken with or without food.

Which drugs or supplements interact with gefitinib?

Gefitinib may increase the blood-thinning effects of warfarin (Coumadin) and increase the risk of bleeding. Therefore, patients receiving gefitinib and warfarin at the same time should have more frequent testing of the "thinness" of their blood.

Patients who receive drugs that increase an enzyme in the liver called CYP 3A4 that destroys gefitinib (for example, rifampin or phenytoin (Dilantin) may need a higher dose of gefitinib to maintain the effectiveness of gefitinib.

Similarly, patients who receive drugs that reduce CYP 3A4, for example, ketoconazole (Nizoral), itraconazole (Sporanox), fluconazole (Diflucan), erythromycin, clarithromycin (Biaxin), ritonavir (Norvir), nelfinavir (Viracept), indinavir (Crixivan), nefazodone (Serzone), as well as grapefruit juice, may need a lower dose of gefitinib to prevent side effects from increased levels of gefitinib.

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