| Drug class |
Third‑generation EGFR tyrosine‑kinase inhibitor (TKI) |
| Indications |
• Metastatic non‑small cell lung cancer (NSCLC) with EGFR exon 19 deletion or L858R substitution or T790M resistance mutation
• First‑line therapy for EGFR‑mutant metastatic NSCLC (based on 2023/2024 approvals) |
| Mechanism of action |
Selectively binds irreversibly to cysteine‑797 in the ATP‑binding pocket of mutant EGFR, blocking downstream signaling while sparing wild‑type EGFR → lower skin/mucositis toxicity. |
| Typical dosing |
80 mg orally once daily, 28‑day cycle (no dose reduction required for most patients, but may be reduced to 40 mg if intolerable side effects). |
| Key pharmacokinetics |
• Absorbed ~70% after oral dose (bioavailability ↑ with food).
• Peak concentration 4–6 h.
• Half‑life 48 h (steady state ~14 days).
• Metabolized mainly by CYP3A4/5 (also CYP2D6, UGT1A1). |
| Common adverse events |
• Diarrhea (most common, usually grade 1–2).
• Skin rash, dry skin, pruritus.
• Paronychia (nail inflammation).
• Interstitial lung disease (rare but serious).
• QTc prolongation (monitor ECG in high‑risk patients). |
| Serious or rare events |
• Interstitial lung disease/pneumonitis (requires immediate discontinuation).
• Hepatotoxicity (monitor LFTs).
• Severe skin reactions (SJS/TEN).
• QTc > 500 ms or symptomatic arrhythmia. |
| Drug–drug interactions |
• Strong CYP3A4 inhibitors (ketoconazole, clarithromycin, ritonavir) ↑ osimertinib levels → consider dose reduction.
• Strong CYP3A4 inducers (rifampin, carbamazepine, phenytoin, St. John’s wort) ↓ levels → may reduce efficacy.
• Nitrates (nitroglycerin, isosorbide) + osimertinib ↑ risk of hypotension.
• QT‑prolonging agents (e.g., azithromycin, ondansetron) ↑ QTc risk. |
| Contraindications |
• Known hypersensitivity to osimertinib or any excipients.
• Severe hepatic impairment (Child‑Pugh C). |
| Special populations |
• Renal: No dose adjustment required.
• Hepatic: Mild–moderate (Child‑Pugh A/B) – no dose change; severe – avoid.
• Pregnancy: Category D – use only if benefits outweigh risks; avoid in breastfeeding. |
| Monitoring |
• Baseline & periodic CBC, LFTs, electrolytes.
• ECG before therapy if QT risk factors.
• Pulmonary assessment (symptoms, imaging) if ILD suspected. |
| Adherence tips |
• Take with food to improve absorption.
• Use a pill organizer or phone alarm.
• Report persistent diarrhea or rash early to manage with antidiarrheals or topical steroids. |
| Patient counseling |
• Explain that the drug targets specific EGFR mutations; efficacy depends on mutation testing.
• Discuss potential side‑effect profile and the importance of promptly reporting severe events (fever, breathing difficulty, rash).
• Emphasize avoiding over‑the‑counter medications that may interact (e.g., cough syrups with CYP3A4 inhibitors). |