Approved indications: In the United States, gefitinib is approved as first-line therapy for adults with metastatic non-small cell lung cancer (NSCLC) whose tumors have EGFR exon 19 deletions or exon 21 (L858R) substitution mutations, confirmed by an FDA-approved test.

Off-label uses: Clinicians may use gefitinib off-label for other EGFR-mutated NSCLC settings (such as after prior treatments or in some brain metastases) and occasionally in research or rare tumor types with EGFR activation, but evidence for these uses is more limited and newer EGFR-targeted drugs are often preferred.

Efficacy expectations: In EGFR-mutated metastatic NSCLC, many patients have tumor shrinkage, with objective response rates around one-half to two-thirds and median progression-free survival close to a year in key studies, and symptom improvement often begins within weeks of starting therapy.

Comparison to other treatments: Compared with standard platinum-based chemotherapy, gefitinib in the right mutation-positive population generally offers higher response rates, longer time before the cancer worsens, and better quality of life, but compared with newer EGFR inhibitors such as osimertinib it often has shorter disease control and less activity in brain metastases, so its use now tends to be in selected situations or where other options are not suitable.

Typical dosing: For adults with metastatic EGFR-mutated NSCLC, the recommended dose is 250 mg by mouth once daily, with or without food, continued until the cancer clearly worsens or side effects become unacceptable.

How to take it: Swallow the tablet whole with water at about the same time each day; for people who cannot swallow tablets, it may be dispersed in a glass of plain water (stirred until the tablet breaks up) and taken immediately, with any remaining liquid rinsed out and drunk, as directed by the prescriber.

Special dosing instructions: Your doctor may temporarily stop gefitinib (often for up to about 2 weeks at a time) or interrupt and restart it if you develop significant side effects such as lung symptoms or abnormal liver tests, and will decide whether and when it is safe to resume.

Kidney and liver considerations: No routine dose change is required for mild kidney problems, but use is cautious in very poor kidney function due to limited data; in patients with moderate or severe liver impairment from cirrhosis, drug levels can be higher, so closer monitoring for side effects is important.

Missed dose guidance: If you miss a dose, take it as soon as you remember unless it is less than about 12 hours until your next scheduled dose; if it is close to the next dose, skip the missed tablet and resume your regular schedule without taking two doses at once.

Overdose: Taking more than prescribed can increase the risk of severe diarrhea, rash, liver injury, or heart rhythm problems, so seek emergency care or contact poison control right away if too many tablets are taken.

Common side effects: The most frequent problems are skin reactions (acne-like rash, dry or itchy skin), diarrhea, nausea, vomiting, decreased appetite, fatigue, and mild changes in liver blood tests; these usually start in the first few weeks of treatment and are often mild to moderate but can occasionally be bothersome.

Serious or rare adverse effects: Seek urgent medical attention for sudden or worsening shortness of breath, cough, and fever (possible interstitial lung disease), signs of liver injury (yellow eyes or skin, dark urine, right upper belly pain), severe or persistent diarrhea or vomiting, black or bloody stools or vomiting blood, severe skin reactions (widespread rash, blistering, peeling, sores in the mouth), eye pain or sudden vision changes, chest pain, fainting, or a very fast or irregular heartbeat.

Warnings and precautions: Gefitinib can cause serious lung inflammation, liver injury, stomach or intestinal perforation or bleeding, eye inflammation or corneal damage, and changes in heart rhythm (QT prolongation), especially in people with existing heart disease, low potassium or magnesium, or those taking other QT-prolonging medicines.

Special populations: Use during pregnancy can harm the unborn baby, so effective contraception is recommended during treatment and for at least 2 weeks after the last dose; breastfeeding is generally not recommended while taking gefitinib because of potential risk to the infant.

Age and organ function: Safety and efficacy are not established in children; in older adults, careful monitoring is needed, and people with moderate to severe liver disease or very poor kidney function should use gefitinib with caution and closer follow-up because drug levels can be higher.

Relative safety compared with other drugs: Compared with traditional chemotherapy, gefitinib causes less hair loss and bone marrow suppression but has more EGFR-related rash, diarrhea, and specific risks such as interstitial lung disease and eye problems, which require prompt recognition and management.

Side-effect reporting and safety updates: Patients in the United States can report side effects to the FDA’s MedWatch program (online or by calling 1-800-FDA-1088) and can check FDA or manufacturer communications for any new safety alerts or changes to prescribing information.

Major drug interactions: Gefitinib is broken down mainly by the liver enzyme CYP3A4 (and partly CYP2D6), so strong CYP3A4 inducers such as rifampin, carbamazepine, phenytoin, and St. John’s wort can lower gefitinib levels and reduce effectiveness, while strong CYP3A4 inhibitors such as ketoconazole, itraconazole, clarithromycin, some HIV protease inhibitors, and possibly large amounts of grapefruit products can raise levels and increase side-effect risk.

Acid-reducing medicines: Because gefitinib dissolves poorly at higher stomach pH, long-term use of proton pump inhibitors and H2 blockers may reduce absorption, and frequent antacid use may also interfere, so prescribers may try to avoid strong acid suppression or carefully time short-acting antacids away from gefitinib doses.

Blood thinners and other high-risk combinations: Gefitinib can enhance the anticoagulant effect of warfarin and possibly other vitamin K antagonists, so more frequent INR monitoring and warfarin dose adjustment may be needed; combining gefitinib with other drugs that affect heart rhythm (QT-prolonging medicines), or with strong CYP3A4 inhibitors or inducers, should be done cautiously with appropriate monitoring.

Other medicines and supplements: Always inform your healthcare team about all prescription drugs, over-the-counter medicines, vitamins, and herbal products (especially those that affect the liver or heart rhythm) before starting gefitinib, and avoid starting or stopping such products without medical advice.

Medical conditions requiring extra caution: Extra care is needed in people with a history of interstitial lung disease or significant chronic lung disease, moderate or severe liver disease, prior serious eye problems, existing heart rhythm disorders or heart failure, or uncontrolled electrolyte disturbances, because gefitinib can worsen these issues.

Monitoring needs: During treatment, doctors commonly monitor liver function tests, watch for respiratory symptoms and skin or eye problems, and in patients at risk for heart rhythm changes may check electrolytes and use electrocardiograms (ECGs), adjusting therapy based on these results.

Q: How long will I need to take gefitinib?
A: Most people continue gefitinib once a day as long as it is controlling the cancer and side effects are manageable, which can be many months or longer, and your doctor will review this regularly with imaging and clinic visits.

Q: How soon might I notice that gefitinib is working?
A: Some symptoms such as cough or shortness of breath may start to improve within a few weeks, but scans are usually done after a couple of months to confirm whether the tumors are shrinking or stable.

Q: Can I drink alcohol while taking gefitinib?
A: Light to moderate alcohol use is not absolutely prohibited, but because both alcohol and gefitinib can affect the liver, many doctors advise limiting or avoiding alcohol and checking liver tests regularly.

Q: What should I do if I develop a rash or diarrhea?
A: Mild rash or loose stools are common and may be managed with moisturizers, sun protection, or anti-diarrheal medicines recommended by your care team, but you should contact your doctor promptly if the rash is painful or widespread or if diarrhea is severe, bloody, or persistent.

Q: Is gefitinib the best EGFR-targeted drug for my lung cancer?
A: Gefitinib is effective for many people with the right EGFR mutation, but newer EGFR inhibitors such as osimertinib may offer longer control and better brain penetration, so your oncology team will choose the most appropriate medicine based on your mutation profile, overall health, and treatment goals.

Storage: Store gefitinib tablets at room temperature (about 68°F to 77°F / 20°C to 25°C), in the original tightly closed container, protected from excess heat and moisture, and out of the reach of children and pets.

Disposal: If you have unused or expired tablets, use a drug take-back program when available or follow your pharmacist’s or local waste authority’s instructions; do not flush tablets down the toilet or throw them loose into household trash unless specifically instructed.