| Effects of other medicinal products on lapatinib Lapatinib is predominantly metabolised by CYP3A (see section 5.2). In healthy volunteers receiving ketoconazole, a strong CYP3A4 inhibitor, at 200 mg twice daily for 7 days, systemic exposure to lapatinib (100 mg daily) was increased approximately 3.6fold, and half-life increased 1.7fold. Coadministration of lapatinib with strong inhibitors of CYP3A4 (e.g. ritonavir, saquinavir, telithromycin, ketoconazole, itraconazole, voriconazole, posaconazole, nefazodone) should be avoided. Coadministration of lapatinib with moderate inhibitors of CYP3A4 should proceed with caution and clinical adverse reactions should be carefully monitored.In healthy volunteers receiving carbamazepine, a CYP3A4 inducer, at 100 mg twice daily for 3 days and 200 mg twice daily for 17 days, systemic exposure to lapatinib was decreased approximately 72%. Coadministration of lapatinib with known inducers of CYP3A4 (e.g. rifampicin, rifabutin, carbamazepine, phenytoin or Hypericum perforatum [St John's wort]) should be avoided.Lapatinib is a substrate for the transport proteins Pgp and BCRP. Inhibitors (ketoconazole, itraconazole, quinidine, verapamil, cyclosporine, erythromycin) and inducers (rifampin, St John's Wort) of these proteins may alter the exposure and/or distribution of lapatinib (see section 5.2). The solubility of lapatinib is pH-dependent. Concomitant treatment with substances that increase gastric pH should be avoided, as lapatinib solubility and absorption may decrease.Effects of lapatinib on other medicinal products Lapatinib inhibits CYP3A4 and CYP2C8 in vitro at clinically relevant concentrations. Coadministration of lapatinib with medicines with narrow therapeutic windows that are substrates of CYP3A4 (e.g. cisapride, pimozide and quinidine) or CYP2C8 (e.g. repaglinide) should be avoided (see sections 4.4 and 5.2). If lapatinib is administered in combination with paclitaxel (175 mg/m2 every three weeks), severe neutropenia may coincide with diarrhoea. This warrants monitoring and early treatment of diarrhoea.Lapatinib inhibits the transport proteins Pgp, BCRP and OATP1B1 in vitro. The clinical relevance of this effect has not been evaluated. It cannot be excluded that lapatinib will affect the pharmacokinetics of substrates of Pgp (e.g. digoxin), BCRP (e.g. topotecan) and OATP1B1 (e.g. rosuvastatin) (see section 5.2). Concomitant administration of lapatinib with capecitabine or trastuzumab did not meaningfully alter the pharmacokinetics of these agents (or the metabolites of capecitabine) or lapatinib.Interactions with food and drink The bioavailability of lapatinib is increased up to about 4 times by food, depending on e.g. the fat content in the meal (see sections 4.2 and 5.2).Grapefruit juice may inhibit CYP3A4 in the gut wall and increase the bioavailability of lapatinib and should therefore be avoided during treatment with lapatinib. | |