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Introduction

Antineoplastic agent; a highly selective, reversible tyrosine kinase inhibitor of human epidermal growth factor receptor type 2 (HER2).

Uses for Tucatinib (Systemic)

Breast Cancer

Used in combination with trastuzumab and capecitabine for the treatment of HER2-positive advanced unresectable or metastatic breast cancer in adults, including those with brain metastases, previously treated with ≥1 anti-HER2-based regimen in the metastatic setting (designated an orphan drug by FDA for this cancer).

Colorectal Cancer

Used in combination with trastuzumab for treatment of adults with RAS wild-type, HER2-positive unresectable or metastatic colorectal cancer that has progressed following treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy.

Accelerated approval based on tumor response rate and durability of response; continued approval may be contingent on verification and description of clinical benefit in confirmatory studies.

Designated an orphan drug by FDA for treatment of HER2-positive colorectal cancer.

Tucatinib (Systemic) Dosage and Administration

General

Pretreatment Screening

• Serum ALT, AST, and bilirubin concentrations.

• Verify pregnancy status in females of reproductive potential.

• In patients with unresectable or metastatic colorectal cancer, confirm presence of specific RAS mutations mutations with an FDA-approved test.

• In patients with unresectable or metastatic colorectal cancer, confirm presence of HER2 overexpression or gene amplification with a laboratory assessment of tumor tissue.

Patient Monitoring

• Serum ALT, AST, and bilirubin concentrations every 3 weeks during therapy, and as clinically indicated.

Premedication and Prophylaxis

• Prophylactic use of antidiarrheal agents not required in principal efficacy study (HER2CLIMB study).

Dispensing and Administration Precautions

• Based on the Institute for Safe Medication Practices (ISMP), tucatinib is a high-alert medication that has a heightened risk of causing significant patient harm when used in error.

Administration

Oral Administration

Administer twice daily, approximately 12 hours apart at the same time each day, without regard to meals.

Swallow tablets intact; do not chew, crush, crack, break, or split.

If a dose of tucatinib is missed or vomited, take the next dose at the regularly scheduled time.

Dosage

Adults

Breast Cancer

Oral

300 mg twice daily in combination with trastuzumab and capecitabine. Continue until disease progression or unacceptable toxicity.

Consult respective manufacturers' labelings or published protocols for information on dosage and method and sequence of administration of other antineoplastic agents used in combination with tucatinib.

May administer capecitabine and tucatinib at the same time. In the HER2CLIMB study, capecitabine 1 g/m² twice daily within 30 minutes after a meal was administered on days 1–14 and trastuzumab 8 mg/kg IV initially, followed by either 6 mg/kg IV or 600 mg by sub-Q injection was administered on day 1 of each 21-day cycle.

Colorectal Cancer

Oral

300 mg twice daily in combination with trastuzumab. Continue until disease progression or unacceptable toxicity.

Consult respective manufacturers' labelings or published protocols for information on dosage and method and sequence of administration of other antineoplastic agents used in combination with tucatinib.

Dosage Modification for Toxicity

Oral

Temporary interruption of therapy, dosage reduction, and/or permanent discontinuance of drug may be necessary. When dosage reduction is necessary, reduce dosage as described in Table 1.

If an adverse reaction occurs, modify dosage accordingly (see Table 2).

Concomitant Use of Drugs Affecting Hepatic Microsomal Enzymes

Avoid concomitant use of tucatinib with potent inhibitors of cytochrome P-450 (CYP) isoenzyme 2C8. If concomitant use cannot be avoided, reduce tucatinib to 100 mg twice daily. If concomitant use of the potent CYP2C8 inhibitor is discontinued, return tucatinib dosage (after 3 elimination half-lives of the CYP2C8 inhibitor) to the dosage used prior to initiation of the CYP2C8 inhibitor.

Special Populations

Hepatic Impairment

Oral

Severe hepatic impairment (Child-Pugh class C): Reduce dosage to 200 mg twice daily.

Mild or moderate hepatic impairment (Child-Pugh class A or B): No dosage adjustment required.

Renal Impairment

Oral

Mild or moderate renal impairment (Cl_cr 30–89 mL/minute using Cockcroft-Gault formula): No dosage adjustment required.

Severe renal impairment (Cl_cr <30 mL/minute using Cockcroft-Gault formula): Combination therapy with tucatinib, capecitabine, and trastuzumab not recommended.

Geriatric Use

No specific dosage recommendations for patients ≥65 years of age.

Contraindications

• None.

Warnings/Precautions

Diarrhea

Severe diarrhea associated with dehydration, hypotension, acute kidney injury, and death reported. Median time to initial onset of diarrhea was 12 days. Median time to resolution of diarrhea was 8 days.

Administer antidiarrheal therapy as clinically indicated if diarrhea occurs during therapy. Perform diagnostic tests to exclude other causes of diarrhea. If diarrhea occurs, temporary interruption, dosage reduction, or permanent discontinuance of therapy may be necessary.

Hepatic Toxicity

Severe hepatotoxicity (i.e., elevations in ALT and/or AST concentrations >5 times the ULN, elevations in serum bilirubin concentrations >3 times the ULN) reported.

Monitor liver function tests (i.e., ALT, AST, bilirubin concentrations) prior to initiation of therapy, every 3 weeks thereafter, and as clinically indicated. If hepatotoxicity occurs, temporary interruption, dosage reduction, or permanent discontinuance of therapy may be necessary.

Fetal/Neonatal Morbidity and Mortality

Based on its mechanism of action and animal findings, tucatinib may cause fetal harm. Embryofetal toxicity and teratogenicity demonstrated in animals.

Avoid pregnancy during therapy. Perform pregnancy test prior to initiating tucatinib therapy in females of reproductive potential. Advise females of reproductive potential and men who are partners of such women to use effective contraception while receiving the drug and for ≥1 week after the last dose of the drug. If used during pregnancy or if patient becomes pregnant, apprise patient of potential fetal hazard.

Impairment of Fertility

Results of animal studies suggest tucatinib may impair male and female fertility.

Specific Populations

Pregnancy

May cause fetal harm.

Avoid pregnancy during therapy. Perform pregnancy test prior to initiating tucatinib therapy in females of reproductive potential.

Advise females of reproductive potential and men who are partners of such women to use effective contraception while receiving the drug and for ≥1 week after the last dose of the drug. If used during pregnancy or if patient becomes pregnant, apprise patient of potential fetal hazard.

Lactation

Not known whether tucatinib or its metabolites distribute into milk, affect milk production, or affect breast-fed infants.

Women should not breast-feed during therapy and for ≥7 days after the last dose of the drug.

Pediatric Use

Safety and efficacy not established in pediatric patients.

Geriatric Use

In the HER2CLIMB study, 26% of tucatinib-treated patients were ≥65 years of age and 2.5% were ≥75 years of age. No overall difference in efficacy relative to younger adults. Serious adverse reactions (e.g., diarrhea, vomiting, nausea) reported more frequently in geriatric patients.

In the MOUNTAINEER study, 12 patients were ≥65 years of age; however, there were too few patients to assess differences in effectiveness or safety.

Hepatic Impairment

Mild or moderate hepatic impairment: Systemic exposure not substantially altered. No dosage adjustment required.

Severe hepatic impairment: Systemic exposure increased by 1.6-fold. Reduce tucatinib dosage to 200 mg twice daily.

Renal Impairment

Mild or moderate renal impairment: Pharmacokinetics not substantially affected. No dosage adjustment required.

Severe renal impairment: Pharmacokinetics not studied.

Common Adverse Effects

Adverse effects (≥20%) of patients with metastatic breast cancer: Diarrhea, palmar-plantar erythrodysesthesia, nausea, hepatotoxicity, vomiting, stomatitis, decreased appetite, anemia, rash.

Adverse effects (≥20%) of patients with unresectable or metastatic colorectal cancer: Diarrhea, fatigue, rash, nausea, abdominal pain, infusion related reactions, pyrexia.

Tucatinib increases S_cr by inhibiting tubular secretion of creatinine. Elevated S_cr concentrations are reversible in most patients following discontinuance of therapy. Use of alternative markers for renal function may be necessary if elevated S_cr concentrations persist.

General

Pretreatment Screening

• Serum ALT, AST, and bilirubin concentrations.

• Verify pregnancy status in females of reproductive potential.

• In patients with unresectable or metastatic colorectal cancer, confirm presence of specific RAS mutations mutations with an FDA-approved test.

• In patients with unresectable or metastatic colorectal cancer, confirm presence of HER2 overexpression or gene amplification with a laboratory assessment of tumor tissue.

Patient Monitoring

• Serum ALT, AST, and bilirubin concentrations every 3 weeks during therapy, and as clinically indicated.

Premedication and Prophylaxis

• Prophylactic use of antidiarrheal agents not required in principal efficacy study (HER2CLIMB study).

Dispensing and Administration Precautions

• Based on the Institute for Safe Medication Practices (ISMP), tucatinib is a high-alert medication that has a heightened risk of causing significant patient harm when used in error.

Administration

Oral Administration

Administer twice daily, approximately 12 hours apart at the same time each day, without regard to meals.

Swallow tablets intact; do not chew, crush, crack, break, or split.

If a dose of tucatinib is missed or vomited, take the next dose at the regularly scheduled time.

Dosage

Adults

Breast Cancer

Oral

300 mg twice daily in combination with trastuzumab and capecitabine. Continue until disease progression or unacceptable toxicity.

Consult respective manufacturers' labelings or published protocols for information on dosage and method and sequence of administration of other antineoplastic agents used in combination with tucatinib.

May administer capecitabine and tucatinib at the same time. In the HER2CLIMB study, capecitabine 1 g/m² twice daily within 30 minutes after a meal was administered on days 1–14 and trastuzumab 8 mg/kg IV initially, followed by either 6 mg/kg IV or 600 mg by sub-Q injection was administered on day 1 of each 21-day cycle.

Colorectal Cancer

Oral

300 mg twice daily in combination with trastuzumab. Continue until disease progression or unacceptable toxicity.

Consult respective manufacturers' labelings or published protocols for information on dosage and method and sequence of administration of other antineoplastic agents used in combination with tucatinib.

Dosage Modification for Toxicity

Oral

Temporary interruption of therapy, dosage reduction, and/or permanent discontinuance of drug may be necessary. When dosage reduction is necessary, reduce dosage as described in Table 1.

If an adverse reaction occurs, modify dosage accordingly (see Table 2).

Concomitant Use of Drugs Affecting Hepatic Microsomal Enzymes

Avoid concomitant use of tucatinib with potent inhibitors of cytochrome P-450 (CYP) isoenzyme 2C8. If concomitant use cannot be avoided, reduce tucatinib to 100 mg twice daily. If concomitant use of the potent CYP2C8 inhibitor is discontinued, return tucatinib dosage (after 3 elimination half-lives of the CYP2C8 inhibitor) to the dosage used prior to initiation of the CYP2C8 inhibitor.

Special Populations

Hepatic Impairment

Oral

Severe hepatic impairment (Child-Pugh class C): Reduce dosage to 200 mg twice daily.

Mild or moderate hepatic impairment (Child-Pugh class A or B): No dosage adjustment required.

Renal Impairment

Oral

Mild or moderate renal impairment (Cl_cr 30–89 mL/minute using Cockcroft-Gault formula): No dosage adjustment required.

Severe renal impairment (Cl_cr <30 mL/minute using Cockcroft-Gault formula): Combination therapy with tucatinib, capecitabine, and trastuzumab not recommended.

Geriatric Use

No specific dosage recommendations for patients ≥65 years of age.

Metabolized principally by CYP2C8 and, to a lesser extent, by CYP3A.

In vitro, reversible inhibitor of CYP isoenzymes 2C8 and 3A. Time-dependent inhibitor of CYP3A, but does not inhibit CYP isoenzymes 1A2, 2B6, 2C9, 2C19, and 2D6, or uridine diphosphate-glucuronosyltransferase (UGT) 1A1.

Substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), but not a substrate of organic anion transporter (OAT) 1, OAT3, organic cation transporter (OCT) 1, OCT3, organic anion transporting polypeptide (OATP) 1B1, OATP1B3, multidrug and toxin extrusion (MATE) 1, MATE2K, or bile salt export pump (BSEP).

Drugs Affecting Hepatic Microsomal Enzymes

Potent CYP2C8 inhibitors: Possible increased systemic exposure to tucatinib and increased risk of adverse effects. Avoid concomitant use. If concomitant use cannot be avoided, reduce tucatinib dosage to 100 mg twice daily. If concomitant use of potent CYP2C8 inhibitor is discontinued, return tucatinib dosage (after 3 elimination half-lives of the CYP2C8 inhibitor) to dosage used prior to initiation of CYP2C8 inhibitor.

Moderate CYP2C8 inhibitors: Possible increased systemic exposure to tucatinib and increased risk of adverse effects. If used concomitantly, monitor for signs of tucatinib toxicity.

Potent CYP3A or moderate CYP2C8 inducers: Possible decreased systemic exposure to tucatinib and reduced efficacy of tucatinib. Avoid concomitant use.

Drugs Metabolized by Hepatic Microsomal Enzymes

Substrates of CYP3A: Possible increased systemic exposure to the CYP3A substrate and increased risk of adverse effects of the substrate drug. Avoid concomitant use with CYP3A substrates that have a narrow therapeutic index. If concomitant use cannot be avoided, reduce dosage of the CYP3A substrate as appropriate.

Drugs Affected by Transport Systems

P-gp substrates: Possible increased systemic exposure of the P-gp substrate and increased risk of adverse effects of the substrate drug. If used concomitantly with a P-gp substrate that has a narrow therapeutic index, reduce dosage of the P-gp substrate as appropriate.

Specific Drugs