indication

Indicated in combination with capecitabine for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress the human epidermal receptor type 2 (HER2) protein and who have received prior therapy including an anthracycline, a taxane, and trastuzuma.

pharmacology

Lapatinib is a small molecule and a member of the 4-anilinoquinazoline class of kinase inhibitors. An anti-cancer drug, lapatinib was developed by GlaxoSmithKline (GSK) as a treatment for solid tumours such as breast and lung cancer. It was approved by the FDA on March 13, 2007, for use in patients with advanced metastatic breast cancer in conjunction with the chemotherapy drug capecitabine.

mechanism of action

Lapatinib is a 4-anilinoquinazoline kinase inhibitor of the intracellular tyrosine kinase domains of both epidermal growth factor receptor (HER1/EGFR/ERBB1) and human epidermal growth factor receptor type 2 (HER2/ERBB2)with a dissociation half-life of ≥300 minutes. Lapatinib inhibits ERBB-driven tumor cell growth in vitro and in various animal models. An additive effect was demonstrated in an in vitro study when lapatinib and 5-florouracil (the active metabolite of capecitabine) were used in combination in the 4 tumor cell lines tested. The growth inhibitory effects of lapatinib were evaluated in trastuzumab-conditioned cell lines. Lapatinib retained significant activity against breast cancer cell lines selected for long-term growth in trastuzumab-containing medium in vitro. These in vitro findings suggest non-cross-resistance between these two agents.

toxicity

There has been a report of one patient who took 3,000 mg of lapatinib for 10 days. This patient had grade 3 diarrhea and vomiting on day 10.

biotransformation

Lapatinib undergoes extensive metabolism, primarily by CYP3A4 and CYP3A5, with minor contributions from CYP2C19 and CYP2C8 to a variety of oxidated metabolites, none of which accounts for more than 14% of the dose recovered in the feces or 10% of lapatinib concentration in plasma.

absorption

Absorption following oral administration of lapatinib is incomplete and variable.

half life

Single-dose terminal half life: 14.2 hours Effective multiple-dose half life: 24 hours

route of elimination

Lapatinib undergoes extensive metabolism, primarily by CYP3A4 and CYP3A5, with minor contributions from CYP2C19 and CYP2C8 to a variety of oxidated metabolites, none of which accounts for more than 14% of the dose recovered in the feces or 10% of lapatinib concentration in plasma.

drug interactions

Artemether: Additive QTc-prolongation may occur. Concomitant therapy should be avoided.

Lumefantrine: Additive QTc-prolongation may occur. Concomitant therapy should be avoided.

Tacrolimus: Additive QTc-prolongation may occur increasing the risk of serious ventricular arrhythmias. Concomitant therapy should be used with caution.

Tamsulosin: Lapatinib, a CYP3A4 inhibitor, may decrease the metabolism and clearance of Tamsulosin, a CYP3A4 substrate. Monitor for changes in therapeutic/adverse effects of Tamsulosin if Lapatinib is initiated, discontinued, or dose changed.

Telithromycin: Telithromycin may reduce clearance of Lapatinib. Consider alternate therapy or monitor for changes in the therapeutic/adverse effects of Lapatinib if Telithromycin is initiated, discontinued or dose changed.

Thiothixene: May cause additive QTc-prolonging effects. Increased risk of ventricular arrhythmias. Consider alternate therapy. Thorough risk:benefit assessment is required prior to co-administration.

Tolterodine: Lapatinib may decrease the metabolism and clearance of Tolterodine. Adjust Tolterodine dose and monitor for efficacy and toxicity.

Topotecan: The p-glycoprotein inhibitor, Lapatinib, may increase the bioavailability of oral Topotecan. A clinically significant effect is also expected with IV Topotecan. Concomitant therapy should be avoided.

Toremifene: Additive QTc-prolongation may occur, increasing the risk of serious ventricular arrhythmias. Consider alternate therapy. A thorough risk:benefit assessment is required prior to co-administration.

Tramadol: Lapatinib may increase Tramadol toxicity by decreasing Tramadol metabolism and clearance.

Trazodone: The CYP3A4 inhibitor, Lapatinib, may increase Trazodone efficacy/toxicity by decreasing Trazodone metabolism and clearance. Monitor for changes in Trazodone efficacy/toxicity if Lapatinib is initiated, discontinued or dose changed.

Tretinoin: The moderate CYP2C8 inhibitor, Lapatinib, may decrease the metabolism and clearance of oral Tretinoin. Monitor for changes in Tretinoin effectiveness and adverse/toxic effects if Lapatinib is initiated, discontinued to dose changed.

Trimipramine: Additive QTc-prolongation may occur, increasing the risk of serious ventricular arrhythmias. Concomitant therapy should be used with caution.

Voriconazole: Voriconazole, a strong CYP3A4 inhibitor, may increase the serum concentration of lapatinib by decreasing its metabolism. Monitor for changes in the therapeutic and adverse effects of lapatinib if voriconazole is initiated, discontinued or dose changed.

Vorinostat: Additive QTc prolongation may occur. Consider alternate therapy or monitor for QTc prolongation as this can lead to Torsade de Pointes (TdP).

Ziprasidone: Additive QTc-prolonging effects may increase the risk of severe arrhythmias. Concomitant therapy is contraindicated.

Zuclopenthixol: Additive QTc prolongation may occur. Consider alternate therapy or use caution and monitor for QTc prolongation as this can lead to Torsade de Pointes (TdP).