The recommended daily dose of Iressa® is one 250mg tablet once daily with or without food.

Gefitinib is an Epidermal Growth Factor Receptor Tyrosine Kinase inhibitor. Epidermal Growth Factor Receptor, or EGFR, is expressed on the surface of normal cells and cancer cells. Increased EGFR signalling can promote tumour growth and cancer spread. Mutations in the tyrosine kinase portion of the EGFR gene are only found in tumour cells. This makes gefitinib able to target tumour cells over normal cells. In patients whose tumour cells contain a mutation of the EGFR-tyrosine kinase gene, gefitinib may be able to lead to tumour shrinkage.

 Along with its therapeutic benefit, gefitinib can cause the following side effects:

• nausea, vomiting, and diarrhea
• mouth sores
• skin rash
• nose bleeds
• hair loss
• dry eyes
• interstitial lung disease

 Tell your doctor immediately if you develop trouble breathing, cough or fever.

Gefitinib should be administered under the supervision of a qualified health professional who is experienced in the treatment and management of patients with cancer.
Before starting gefitinib, your doctor will run a test to deterimine if your tumour cells have the activating EGFR-TK mutation. Only patients with this mutation should be treated with gefitinib.

There have been cases of patients treated with gefitinib developing Insterstitial Lung Disease. Approximately 1/3 of the cases have been fatal. If patients taking gefitinib develop worsening of respiratory symptoms such as shortness of breath, cough and fever, gefitinib therapy should be interrupted. If a diagnosis of Interstitial Lung Disease is made, then the patient must discontinue gefitinib.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• lung disease (e.g., pulmonary fibrosis)
• severe kidney disease,
• eye problems,
• stomach/intestinal ulcers, other stomach/intestinal problems (such as diverticulitis, blockage, bowel disease),
• smoking,
• cancer that has spread to the bowels.

Gefitinib may interact with other medications: 

• blood thinners (warfarin),
• drugs which reduce stomach acid (e.g., ranitidine, cimetidine, famotidine, omeprazole, lansoprazole, rabeprazole),
• certain liver enzyme inhibitors such as ketoconazole, itraconazole, erythromycin, clarithromycin)
• oral anti-inflammatory medications (such as ibuprofen, naproxen),
• corticosteroids (such as prednisone)
• rifampin, St. John's wort or phenytoin

Do not use if pregnant or breastfeeding.   Take precautions against conceiving while taking this medication. (Men and women)