Iressa

[gefitinib tablets]

In patients receiving a potent CYP3A4 inducer such as rifampicin or phenytoin, a dose increase to 500 mg daily should be considered in the absence of severe adverse drug reaction, and clinical response and adverse events should be carefully monitored (see CLINICAL PHARMA-COLOGY- Pharmacokinetics-Drug-Drug Interactions and DOSAGE AND ADMIN-ISTRATION- Dosage Adjustment sections). International Normalized Ratio (INR) elevations and/ or bleeding events have been reported in some patients taking warfarin while on IRESSA therapy.

Patients taking warfarin should be monitored regularly for changes in prothrombin time or INR (see CLINICAL PHARMACOLOGY-Pharmacokinetics- Drug-Drug Interactions and ADVERSE REACTIONS sections). Substances that are potent inhibitors of CYP3A4 activity (eg, ketoconazole and itraconazole) decrease gefitinib metabolism and increase gefitinib plasma concentra-tions.

This increase may be clinically relevant as adverse experiences are related to dose and exposure; therefore, caution should be used when administering CYP3A4 inhibitors with IRESSA (see CLINICAL PHARMACOLOGY-Pharmacokinetics-Drug- Drug Interactions and ADVERSE REACTIONS sections). Drugs that cause significant sustained elevation in gastric pH (histamine H 2 -receptor antagonists such as ranitidine or cimetidine) may reduce plasma concentrations of IRESSA and therefore potentially may reduce efficacy (see CLINICAL PHARMA-COLOGY- Drug-Drug Interactions section).

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Carcinogenesis, Mutagenesis, Impairment of Fertility

Gefitinib has been tested for genotoxicity in a series of in vitro (bacterial mutation, mouse lymphoma, and human lymphocyte) assays and an in vivo rat micronucleus test. Under the conditions of these assays, gefitinib did not cause genetic damage. Carcinogenicity studies have not been conducted with gefitinib.

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