1. Name Of The Medicinal Product
Tyverb
2. Qualitative And Quantitative Composition
Each film-coated tablet contains lapatinib ditosylate monohydrate, equivalent to 250 mg lapatinib.
For a full list of excipients, see section 6.1.
3. Pharmaceutical Form
Film-coated tablet (tablet).
Oval, biconvex, yellow film-coated tablets, with “GS XJG” debossed on one side.
4. Clinical Particulars
4.1 Therapeutic Indications
Tyverb is indicated for the treatment of patients with breast cancer, whose tumours overexpress HER2 (ErbB2);
• in combination with capecitabine for patients with advanced or metastatic disease with progression following prior therapy, which must have included anthracyclines and taxanes and therapy with trastuzumab in the metastatic setting (see section 5.1).
• in combination with an aromatase inhibitor for postmenopausal women with hormone receptor positive metastatic disease, not currently intended for chemotherapy. The patients in the registration study were not previously treated with trastuzumab or an aromatase inhibitor (See section 5.1).
4.2 Posology And Method Of Administration
Tyverb treatment should only be initiated by a physician experienced in the administration of anti-cancer agents.
HER2 (ErbB2) overexpressing tumours are defined by IHC3+, or IHC2+ with gene amplification or gene amplification alone. HER2 status should be determined using accurate and validated methods.
The daily dose of Tyverb should not be divided. Tyverb should be taken either at least one hour before, or at least one hour after food. To minimise variability in the individual patient, administration of Tyverb should be standardised in relation to food intake, for example always to be taken one hour before a meal (see sections 4.5 and 5.2 for information on absorption).
Missed doses should not be replaced and the dosing should resume with the next scheduled daily dose (see section 4.9).
Consult the full prescribing information of the co-administered medicinal product for relevant details of their posology including any dose reductions, contraindications and safety information.
Tyverb / capecitabine combination posology
The recommended dose of Tyverb is 1250 mg (i.e. five tablets) once daily continuously.
The recommended dose of capecitabine is 2000 mg/m2/day taken in 2 doses 12 hours apart on days 1-14 in a 21 day cycle (see section 5.1). Capecitabine should be taken with food or within 30 minutes after food. Please refer to the full prescribing information of capecitabine.
Tyverb / aromatase inhibitor combination posology
The recommended dose of Tyverb is 1500 mg (i.e. six tablets) once daily continuously.
Please refer to the full prescribing information of the co-administered aromatase inhibitor for dosing details.
Dose delay and dose reduction
Cardiac events
Tyverb should be discontinued in patients with symptoms associated with decreased left ventricular ejection fraction (LVEF) that are National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) grade 3 or greater or if their LVEF drops below the institutions lower limit of normal (see section 4.4). Tyverb may be restarted at a reduced dose (1000 mg/day when administered with capecitabine or 1250 mg/day when administered with an aromatase inhibitor) after a minimum of 2 weeks and if the LVEF recovers to normal and the patient is asymptomatic.
Interstitial lung disease / pneumonitis
Tyverb should be discontinued in patients who experience pulmonary symptoms which are NCI CTCAE grade 3 or greater (see section 4.4).
Other toxicities
Discontinuation or interruption of dosing with Tyverb may be considered when a patient develops toxicity greater than or equal to grade 2 on the NCI CTCAE. Dosing can be restarted, when the toxicity improves to grade 1 or less, at either 1250 mg/day when administered with capecitabine or 1500 mg/day when administered with an aromatase inhibitor. If the toxicity recurs, then Tyverb should be restarted at a lower dose (1000 mg/day when administered with capecitabine or 1250 mg/day when administered with an aromatase inhibitor).
Renal impairment
No dose adjustment is necessary in patients with mild to moderate renal impairment. Caution is advised in patients with severe renal impairment as there is no experience of Tyverb in this population (see section 5.2).
Hepatic impairment
Tyverb should be discontinued if changes in liver function are severe and patients should not be retreated (see section 4.4).
Administration of Tyverb to patients with moderate to severe hepatic impairment should be undertaken with caution due to increased exposure to the medicinal product. Insufficient data are available in patients with hepatic impairment to provide a dose adjustment recommendation (see section 5.2).
Paediatric Population
Tyverb is not recommended for use in the paediatric population due to insufficient data on safety and efficacy.
Elderly
There are limited data of the use of Tyverb and capecitabine in patients aged
In the phase III clinical study of Tyverb in combination with letrozole, of the total number of hormone receptor positive metastatic breast cancer patients (Intent to treat population N=642), 44 % were
4.3 Contraindications
Hypersensitivity to the active substance or to any of the excipients.
4.4 Special Warnings And Precautions For Use
Lapatinib has been associated with reports of decreases in left ventricular ejection fraction (LVEF) (see section 4.8). Lapatinib has not been evaluated in patients with symptomatic cardiac failure. Caution should be taken if Tyverb is to be administered to patients with conditions that could impair left ventricular function (including coadministration with potentially cardiotoxic agents). Evaluation of cardiac function, including LVEF determination, should be conducted for all patients prior to initiation of treatment with Tyverb to ensure that the patient has a baseline LVEF that is within the institutions normal limits. LVEF should continue to be evaluated during treatment with Tyverb to ensure that LVEF does not decline to an unacceptable level (see section 4.2). In some cases, LVEF decrease may be severe and lead to cardiac failure. Fatal cases have been reported, causality of the deaths is uncertain.
There has been no dedicated study to assess the potential for lapatinib to prolong the QT interval. A small, concentration dependent increase in QTc interval was observed in an uncontrolled, open-label dose-escalation study of lapatinib in advanced cancer patients, such that an effect on QT interval cannot be ruled out. Caution should be taken if Tyverb is administered to patients with conditions that could result in prolongation of QTc (including hypokalemia, hypomagnesemia, congenital long QT syndrome, or coadministration of other medicines known to cause QT prolongation). Hypokalemia or hypomagnesemia should be corrected prior to treatment. Electrocardiograms with QT measurement should be considered prior to administration of Tyverb and throughout treatment.
Lapatinib has been associated with reports of pulmonary toxicity including interstitial lung disease and pneumonitis (see section 4.8). Patients should be monitored for symptoms of pulmonary toxicity (dyspnoea, cough, fever) and treatment discontinued in patients who experience symptoms which are NCI CTCAE grade 3 or greater. Pulmonary toxicity may be severe and lead to respiratory failure. Fatal cases have been reported, causality of the deaths is uncertain.
Hepatotoxicity has occurred with Tyverb use and may in rare cases be fatal. At the initiation of treatment patients should be advised of the potential for hepatotoxicity. Liver function (transaminases, bilirubin and alkaline phosphatase) should be monitored before the initiation of treatment and monthly thereafter, or as clinically indicated. Tyverb dosing should be discontinued if changes in liver function are severe and patients should not be retreated.
Caution is warranted if Tyverb is prescribed to patients with moderate or severe hepatic impairment (see sections 4.2 and 5.2).
Caution is advised if Tyverb is prescribed to patients with severe renal impairment (see sections 4.2 and 5.2).
Diarrhoea, including severe diarrhoea, has been reported with Tyverb treatment (see section 4.8). At the start of therapy, the patients bowel pattern and any other symptoms (e.g. fever, cramping pain, nausea, vomiting, dizziness and thirst) should be determined, to allow identification of changes during treatment and to help identify patients at greater risk of diarrhoea. Patients should be instructed to promptly report any change in bowel patterns. Proactive management of diarrhoea with anti-diarrhoeal agents is important. Severe cases of diarrhoea may require administration of oral or intravenous electrolytes and fluids, and interruption or discontinuation of Tyverb therapy (see section 4.2 – dose delay and dose reduction – other toxicities).
Concomitant treatment with inducers of CYP3A4 should be avoided due to risk of decreased exposure to lapatinib (see section 4.5).
Concomitant treatment with strong inhibitors of CYP3A4 should be avoided due to risk of increased exposure to lapatinib (see section 4.5).
Grapefruit juice should be avoided during treatment with Tyverb (see section 4.5).
Coadministration of Tyverb with orally administered medicinal products with narrow therapeutic windows that are substrates of CYP3A4 should be avoided (see section 4.5).
Coadministration of Tyverb with medicinal products with narrow therapeutic windows that are substrates of CYP2C8 should be avoided (see section 4.5).
Concomitant treatment with substances that increase gastric pH should be avoided, as lapatinib solubility and absorption may decrease (see section 4.5).
4.5 Interaction With Other Medicinal Products And Other Forms Of Interaction
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 3.6–fold, and half-life increased 1.7–fold. Coadministration of Tyverb with strong inhibitors of CYP3A4 (e.g. ritonavir, saquinavir, telithromycin, ketoconazole, itraconazole, voriconazole, posaconazole, nefazodone) should be avoided. Coadministration of Tyverb 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 Tyverb 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 (rifampicin, 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. Pre-treatment with a proton pump inhibitor (esomeprazole) decreased lapatinib exposure by an average of 27% (range: 6% to 49%). This effect decreases with increasing age from approximately 40 to 60 years.
Effects of lapatinib on other medicinal products
Lapatinib inhibits CYP3A4 in vitro at clinically relevant concentrations. Coadministration of Tyverb with orally administered midazolam resulted in an approximate 45% increase in the AUC of midazolam. There was no clinically meaningful increase in AUC when midazolam was dosed intravenously. Coadministration of Tyverb with orally administered medicines with narrow therapeutic windows that are substrates of CYP3A4 (e.g. cisapride, pimozide and quinidine) should be avoided (see sections 4.4 and 5.2).
Lapatinib inhibits CYP2C8 in vitro at clinically relevant concentrations. Coadministration of Tyverb with medicines with narrow therapeutic windows that are substrates of CYP2C8 (e.g. repaglinide) should be avoided (see sections 4.4 and 5.2).
Coadministration of lapatinib with intravenous paclitaxel increased the exposure of paclitaxel by 23%, due to lapatinib inhibition of CYP2C8 and/or Pgp. An increase in the incidence and severity of diarrhoea and neutropenia has been observed with this combination in clinical trials. Caution is advised if lapatinib is coadministered with paclitaxel.
Coadministration of lapatinib with intravenously administered docetaxel did not significantly affect the AUC or Cmax of either active substance. However, the occurrence of docetaxel-induced neutropenia was increased.
Coadministration of Tyverb with irinotecan (when administered as part of the FOLFIRI regimen) resulted in an approximate 40% increase in the AUC of SN-38, the active metabolite of irinotecan. The precise mechanism of this interaction is unknown, but it is assumed to be due to inhibition of one or more transport proteins by lapatinib. Adverse reactions should be carefully monitored if Tyverb is coadministered with irinotecan, and a reduction in the dose of irinotecan should be considered.
Lapatinib inhibits the transport protein Pgp in vitro at clinically relevant concentrations. Coadministration of lapatinib with orally administered digoxin resulted in an approximate 80% increase in the AUC of digoxin. Caution should be exercised when dosing lapatinib concurrently with medications with narrow therapeutic windows that are substrates of Pgp, and a reduction in the dose of the Pgp substrate should be considered.
Lapatinib inhibits the transport proteins 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 BCRP (e.g. topotecan) and OATP1B1 (e.g. rosuvastatin) (see section 5.2).
Concomitant administration of Tyverb with capecitabine, letrozole 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 Tyverb.
4.6 Pregnancy And Lactation
There are no adequate data from the use of Tyverb in pregnant women. Studies in animals have shown reproductive toxicity (see section 5.3). The potential risk for humans is not known.
Tyverb should not be used during pregnancy unless clearly necessary. Women of childbearing potential should be advised to use adequate contraception and avoid becoming pregnant while receiving treatment with Tyverb.
The safe use of Tyverb during breast-feeding has not been established. It is not known whether lapatinib is excreted in human milk. In rats, growth retardation was observed in pups which were exposed to lapatinib via breast milk. Breast-feeding must be discontinued in women who are receiving therapy with Tyverb.
4.7 Effects On Ability To Drive And Use Machines
No studies on the effects of lapatinib on the ability to drive and use machines have been performed. A detrimental effect on such activities cannot be predicted from the pharmacology of lapatinib. The clinical status of the patient and the adverse event profile of lapatinib should be borne in mind when considering the patient's ability to perform tasks that require judgement, motor or cognitive skills.
4.8 Undesirable Effects
The safety of lapatinib has been evaluated as monotherapy or in combination with other chemotherapies for various cancers in more than 11,000 patients, including 198 patients who received lapatinib in combination with capecitabine and 654 patients who received lapatinib in combination with letrozole (see section 5.1).
The most common adverse reactions (>25%) during therapy with lapatinib were gastrointestinal events (such as diarrhoea, nausea, and vomiting) and rash. Palmar-plantar erythrodysesthesia [PPE] was also common (>25%) when lapatinib was administered in combination with capecitabine. The incidence of PPE was similar in the lapatinib plus capecitabine and capecitabine alone treatment arms. Diarrhoea was the most common adverse reaction resulting in discontinuation of treatment when lapatinib was administered in combination with capecitabine, or with letrozole.
The following convention has been utilised for the classification of frequency: Very common ((
Within each frequency grouping, undesirable effects are presented in order of decreasing seriousness.
The following adverse reactions have been reported to have a causal association with lapatinib alone or lapatinib in combination with capecitabine or letrozole.
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*These adverse reactions were observed when lapatinib was administered in combination with capecitabine.
†These adverse reactions were observed when lapatinib was administered in combination with letrozole.
Decreased left ventricular ejection fraction and QT interval prolongation
Left ventricular ejection fraction (LVEF) decreases have been reported in approximately 1% of patients receiving lapatinib and were asymptomatic in more than 90% of cases. LVEF decreases resolved or improved in more than 70 % of cases, in 60 % of these on discontinuation of treatment with lapatinib, and in 40 % of cases lapatinib was continued. Symptomatic LVEF decreases were observed in approximately 0.2% of patients who received lapatinib monotherapy or in combination with other anti-cancer agents. Observed symptoms included dyspnoea, cardiac failure and palpitations. Overall 58 % of these symptomatic subjects recovered. LVEF decreases were reported in 2.5 % of patients who received lapatinib in combination with capecitabine, as compared to 1.0 % with capecitabine alone. LVEF decreases were reported in 3.1 % of patients who received lapatinib in combination with letrozole as compared to 1.3 % of patients receiving letrozole plus placebo.
A small, concentration dependent increase in QTc interval was observed in a phase I uncontrolled study. The potential for lapatinib to prolong the QTc interval has not been ruled out (see section 4.4).
Diarrhoea
Diarrhoea occurred in approximately 65 % of patients who received lapatinib in combination with capecitabine and in 64 % of patients who received lapatinib in combination with letrozole. Most cases of diarrhoea were grade 1 or 2 and did not result in discontinuation of treatment with lapatinib. Diarrhoea responds well to proactive management (see section 4.4). However, a few cases of acute renal failure have been reported secondary to severe dehydration due to diarrhoea.
Rash
Rash occurred in approximately 28 % of patients who received lapatinib in combination with capecitabine and in 45 % of patients who received lapatinib in combination with letrozole. Rash was generally low grade and did not result in discontinuation of treatment with lapatinib. Prescribing physicians are advised to perform a skin examination prior to treatment and regularly during treatment. Patients experiencing skin reactions should be encouraged to avoid exposure to sunlight and apply broad spectrum sunscreens with a Sun Protection Factor (SPF)
4.9 Overdose
There is no specific antidote for the inhibition of EGFR (ErbB1) and/or HER2 (ErbB2) tyrosine phosphorylation. The maximum oral dose of lapatinib that has been administered in clinical trials is 1800 mg once daily.
Asymptomatic and symptomatic cases of overdose have been reported in patients being treated with Tyverb. In patients who took up to 5000 mg of lapatinib, symptoms observed include known lapatinib associated events (see Section 4.8) and in some cases sore scalp and/or mucosal inflammation. In a single case of a patient who took 9000 mg of Tyverb, sinus tachycardia (with otherwise normal ECG) was also observed.
Lapatinib is not significantly renally excreted and is highly bound to plasma proteins, therefore haemodialysis would not be expected to be an effective method to enhance the elimination of lapatinib.
Further management should be as clinically indicated or as recommended by the national poisons centre, where available.
5. Pharmacological Properties
5.1 Pharmacodynamic Properties
Pharmacotherapeutic group: Protein kinase inhibitor, ATC code: L01XE07
This medicinal product has been authorised under a so-called “conditional approval” scheme.
This means that further evidence on this medicinal product is awaited.
The European Medicines Agency (EMA) will review new information on the product every year and this SPC will be updated as necessary.
The European Medicines Agency has waived the obligation to submit the results of studies with Tyverb in all subsets of the paediatric population in the treatment of breast carcinoma (see section 4.2 for information on paediatric use).
Mechanism of action
Lapatinib, a 4-anilinoquinazoline, is an inhibitor of the intracellular tyrosine kinase domains of both EGFR (ErbB1) and of HER2 (ErbB2) receptors (estimated Kiapp values of 3nM and 13nM, respectively) with a slow off-rate from these receptors (half-life greater than or equal to 300 minutes). Lapatinib inhibits ErbB-driven tumour cell growth in vitro and in various animal models.
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.
Clinical studies
Combination treatment with Tyverb and capecitabine
The efficacy and safety of Tyverb in combination with capecitabine in breast cancer patients with good performance status was evaluated in a randomised, phase III trial. Patients eligible for enrolment had HER2-overexpressing, locally advanced or metastatic breast cancer, progressing after prior treatment that included taxanes, anthracyclines and trastuzumab. LVEF was evaluated in all patients (using echocardiogram or MUGA) prior to initiation of treatment with Tyverb to ensure baseline LVEF was within the institutions normal limits. In the clinical trial LVEF was monitored at approximately eight week intervals during treatment with Tyverb to ensure it did not decline to below the institutions lower limit of normal. The majority of LVEF decreases (greater than 60 %) were observed during the first nine weeks of treatment, however limited data was available for long term exposure.
Patients were randomised to receive either Tyverb 1250 mg once daily (continuously) plus capecitabine (2000 mg/m2/day on days 1-14 every 21 days), or to receive capecitabine alone (2500 mg/m2/day on days 1-14 every 21 days). The primary endpoint was time to progression (TTP). Assessments were undertaken by the study investigators and by an independent review panel, blinded to treatment. The study was halted based on the results of a pre-specified interim analysis that showed an improvement in TTP for patients receiving Tyverb plus capecitabine. An additional 75 patients were enrolled in the study between the time of the interim analysis and the end of the enrolment. Investigator analysis on data at the end of enrolment is presented in Table 1.
Table 1 Time to Progression data from Study EGF100151 (Tyverb / capecitabine)
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The independent assessment of the data also demonstrated that Tyverb when given in combination with capecitabine significantly increased time to progression (Hazard Ratio 0.57 [95 % Cl 0.43, 0.77] p=0.0001) compared to capecitabine alone.
Results of an updated analysis of the overall survival data to 28 September 2007 are presented in Table 2.
Table 2 Overall survival data from Study EGF100151 (Tyverb / capecitabine)
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On the combination arm, there were 4 (2%) progressions in the central nervous system as compared with the 13 (6%) progressions on the capecitabine alone arm.
Combination treatment with Tyverb and letrozole
Tyverb has been studied in combination with letrozole for the treatment of postmenopausal women with hormone receptor-positive (oestrogen receptor [ER] positive and / or progesterone receptor [PgR] positive) advanced or metastatic breast cancer.
The Phase III study (EGF30008) was randomised, double-blind, and placebo controlled. The study enrolled patients who had not received prior therapy for their metastatic disease. The period of enrolment to the trial (December 2003 – December 2006) preceded the adoption of trastuzumab in combination with an aromatase inhibitor. A comparative study between lapatinib and trastuzumab in this patient population has not been conducted.
In the HER2-overexpressing population, only 2 patients were enrolled who had received prior trastuzumab, 2 patients had received prior aromatase inhibitor therapy, and approximately half had received tamoxifen.
Patients were randomised to letrozole 2.5 mg once daily plus Tyverb 1500 mg once daily or letrozole with placebo. Randomisation was stratified by sites of disease and by time from discontinuation of prior adjuvant anti-oestrogen therapy. HER2 receptor status was retrospectively determined by central laboratory testing. Of all patients randomised to treatment, 219 patients had tumours overexpressing the HER2 receptor, and this was the pre-specified primary population for the analysis of efficacy. There were 952 patients with HER2-negative tumours, and a total of 115 patients whose tumour HER2 status was unconfirmed (no tumour sample, no assay result, or other reason).
In patients with HER2-overexpressing MBC, investigator-determined progression-free survival (PFS) was significantly greater with letrozole plus Tyverb compared with letrozole plus placebo. In the HER2-negative population, there was no benefit in PFS when letrozole plus Tyverb was compared with letrozole plus placebo (see Table 3).
Table 3 Progression Free Survival data from Study EGF30008 (Tyverb / letrozole)
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CI= confidence interval
HER2 overexpression = IHC 3+ and/or FISH positive; HER2 negative = IHC 0, 1+ or 2+ and/or FISH negative
Clinical Benefit Rate was defined as complete plus partial response plus stable disease for
At the time of analysis, the overall survival data were not mature and there was no significant difference between treatment groups (Tyverb + letrozole combination HR= 0.77 [95 %CI 0.52-1.14] p=0.185). However, no negative effect on overall survival was apparent.
5.2 Pharmacokinetic Properties
The absolute bioavailability following oral administration of lapatinib is unknown, but it is incomplete and variable (approximately 70% coefficient of variation in AUC). Serum concentrations appear after a median lag time of 0.25 hours (range 0 to 1.5 hours). Peak plasma concentrations (Cmax) of lapatinib are achieved approximately 4 hours after administration. Daily dosing of 1250 mg produces steady state geometric mean (coefficient of variation) Cmax values of 2.43 (76%) µg/ml and AUC values of 36.2 (79%) µg*hr/ml.
Systemic exposure to lapatinib is increased when administered with food. Lapatinib AUC values were approximately 3- and 4-fold higher (Cmax approximately 2.5 and 3–fold higher) when administered with a low fat (5% fat [500 calories]) or with a high fat (50% fat [1,000 calories]) meal, respectively.
Lapatinib is highly bound (greater than 99%) to albumin and alpha-1 acid glycoprotein. In vitro studies indicate that lapatinib is a substrate for the transporters BCRP (ABCG1) and p-glycoprotein (ABCB1). Lapatinib has also been shown in vitro to inhibit these efflux transporters, as well as the hepatic uptake transporter OATP 1B1, at clinically relevant concentrations (IC50 values were equal to 2.3 µg/ml). The clinical significance of these effects on the pharmacokinetics of other medicinal products or the pharmacological activity of other anti-cancer agents is not known.
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 account for more than 14% of the dose recovered in the faeces or 10% of lapatinib concentration in plasma.
Lapatinib inhibits CYP3A (Ki 0.6 to 2.3 µg/ml) and CYP2C8 (0.3 µg/ml) in vitro at clinically relevant concentrations. Lapatinib did not significantly inhibit the following enzymes in human liver microsomes: CYP1A2, CYP2C9, CYP2C19, and CYP2D6 or UGT enzymes (in vitro IC50 values were greater than or equal to 6.9 µg/ml).
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