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Z18 Pill: Efficacy and Tolerability of ZD1839 (Iressa) in Cancer Treatment
Introduction to ZD1839 (Iressa)
ZD1839, commonly known as Iressa, is an oral selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor. It has been extensively studied for its potential in treating various solid malignant tumors, particularly non-small-cell lung cancer (NSCLC) and other EGFR-expressing cancers .
Pharmacokinetics and Administration
Pharmacokinetic Profile
ZD1839 exhibits a dose-proportional pharmacokinetic profile. Peak plasma concentrations (Cmax) are typically reached between 3 to 7 hours post-administration, with a terminal elimination half-life (t1/2) ranging from 28 to 48 hours . This pharmacokinetic behavior supports the feasibility of once-daily oral dosing .
Effect of Food on Bioavailability
The bioavailability of ZD1839 is slightly affected by food intake, with a reduction in Cmax by 34% and area under the concentration-time curve (AUC) by 14%. However, the elimination half-life remains unaffected, indicating that food does not significantly alter the drug's overall pharmacokinetic profile.
Safety and Tolerability
Common Adverse Events
The most frequently reported adverse events associated with ZD1839 are mild to moderate in severity, including diarrhea, rash, and nausea. These side effects are generally manageable and reversible upon cessation of treatment . Dose-limiting toxicities (DLTs) such as grade 3 diarrhea and somnolence have been observed at higher doses (≥800 mg/day) .
Dose Escalation and Maximum Tolerated Dose
In phase I trials, dose escalation studies identified 600 mg/day as a tolerable dose with manageable side effects. Doses above this threshold, particularly at 800 mg/day and 1,000 mg/day, resulted in increased incidence of DLTs, necessitating dose reductions in a significant proportion of patients .
Efficacy in Cancer Treatment
Non-Small-Cell Lung Cancer (NSCLC)
ZD1839 has shown promising antitumor activity in patients with NSCLC. Partial responses were observed in several patients, with some achieving prolonged stable disease. In one study, 16 patients remained on treatment for three months or longer, with seven patients continuing for six months or more .
Other Solid Tumors
While the primary focus has been on NSCLC, ZD1839 has also demonstrated efficacy in other solid tumors, including head and neck, ovarian, prostate, and colorectal cancers. Disease stabilization was observed across various tumor types, with some patients maintaining stable disease for extended periods .
Colorectal Cancer
In a phase II trial involving patients with metastatic colorectal cancer, ZD1839 did not result in significant tumor regression. However, a subset of patients achieved stable disease, highlighting the potential for disease control in heavily pre-treated populations.
Conclusion
ZD1839 (Iressa) is a well-tolerated and effective EGFR tyrosine kinase inhibitor with a favorable pharmacokinetic profile suitable for once-daily oral administration. It has shown significant antitumor activity, particularly in NSCLC, and offers a manageable safety profile. Ongoing studies aim to further elucidate its efficacy and optimal dosing in various cancer types.
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