General

Genetic Implications:

Pronunciation:
fam tras-tu-zoo-mab de-rux-te-can

Trade Name(s)

• Enhertu

Ther. Class.
antineoplastics

Pharm. Class.
monoclonal antibodies
enzyme inhibitors

Indications

•  Unresectable or metastatic human epidermal growth factor receptor 2 (HER2)-positive breast cancer in patients who have previously received ≥2 anti-HER2-based regimens in the metastatic setting.
• Locally advanced or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma in patients who have previously received a trastuzumab-based regimen.

Action

Acts as a HER2-directed antibody-drug conjugate composed of a humanized IgG1 monoclonal antibody (which has the same amino acid sequence as trastuzumab [and targets HER2]), a cleavable linker, and a topoisomerase I inhibitor (DXd) (the cytotoxic component which causes DNA damage and apoptosis).

Therapeutic Effect(s):

• Regression of breast cancer and metastases.
• Improved survival in gastric or gastroesophageal junction adenocarcinoma.

Pharmacokinetics

Absorption: IV administration results in complete bioavailability.

Distribution: Minimally distributed to extravascular tissues.

Protein Binding: 97%.

Metabolism and Excretion: Monoclonal antibody component is degraded into smaller peptides via catabolism. DxD primarily metabolized by the liver via CYP3A4 isoenzyme. Excretion pathway unknown.

Half-life: Fam-trastuzumab deruxtecan– 5.7 days;  DXd– 5.8 days.

TIME/ACTION PROFILE (plasma concentrations)

Contraindication/Precautions

Contraindicated in:

• OB:  Pregnancy (may cause fetal harm);
• Lactation: Lactation.

Use Cautiously in:

• Severe renal impairment (CCr <30 mL/min)
• Severe hepatic impairment (total bilirubin >3–10x ULN or AST > ULN)
• Rep:  Women of reproductive potential and men with female partners of reproductive potential;
• Pedi:  Safety and effectiveness not established in children;
• Geri:  Older adults may have ↑ risk of adverse reactions.

Exercise Extreme Caution in:

Pre-existing cardiac dysfunction.

Adverse Reactions/Side Effects

CV: HF

Derm: alopecia, rash

EENT: dry eye, epistaxis

F and E: hypokalemia

GU: ↓ fertility (males)

GI: abdominal pain, constipation, diarrhea, dyspepsia, ↑ liver enzymes, nausea, stomatitis, vomiting

Hemat: NEUTROPENIA, anemia, leukopenia, thrombocytopenia

Metabolic: ↓ appetite

Neuro: dizziness, headache

Resp: INTERSTITIAL LUNG DISEASE/PNEUMONITIS, cough, dyspnea, upper respiratory tract infection

Misc: fatigue

* CAPITALS indicate life-threatening.
Underline indicate most frequent.

Interactions

Drug-Drug

None reported.

Route/Dosage

Do NOT substitute fam-trastuzumab deruxtecan with trastuzumab or ado-trastuzumab emtansine.

Metastatic Breast Cancer

IV (Adults): 5.4 mg/kg every 3 wk. Continue until disease progression or unacceptable toxicity.

Locally Advanced or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

IV (Adults): 6.4 mg/kg every 3 wk. Continue until disease progression or unacceptable toxicity.

Availability

Lyophilized powder for injection: 100 mg/vial

Assessment

• Assess for signs and symptoms of interstitial lung disease (ILD)/pneumonitis (cough, dyspnea, fever, and/or any new or worsening respiratory symptoms) periodically during therapy. If asymptomatic (Grade 1), hold medication until resolved to Grade 0, then: if resolved in <28 days from date of onset, maintain dose. If resolved in >28 days from date of onset, reduce dose one level. Consider corticosteroid therapy as soon as ILD/pneumonitis is suspected. If symptomatic ILD/pneumonitis occurs (≥Grade 2), discontinue therapy permanently and start corticosteroid therapy.
• Assess for signs and symptoms of left ventricular dysfunction (LVEF) before starting and at regular intervals during therapy as clinically indicated. If LVEF >45% and absolute decrease from baseline is 10–20%, continue with therapy. If LVEF is 40–45% and absolute decrease from baseline is <10%, continue with therapy. Repeat LVEF assessment within 3 wk. If LVEF is 40–45% and absolute decrease from baseline is 10–20%, hold therapy and repeat LVEF assessment within 3 wk. If LVEF has not recovered to within 10% from baseline, permanently discontinue therapy. If LVEF recovers to within 10% from baseline, resume therapy at the same dose. If LVEF <40% or absolute decrease from baseline >20%, hold therapy and repeat LVEF assessment within 3 wk. If LVEF <40% or absolute decrease from baseline of >20% is confirmed, permanently discontinue therapy. If symptomatic HF occurs, discontinue therapy permanently.

Lab Test Considerations:

Verify negative pregnancy test before starting therapy.

•  Patient selection for patients with locally advanced or metastatic gastric cancer is based on HER2 protein overexpression or HER2 gene amplification. Reassess HER2 status if it is feasible to obtain a new tumor specimen after prior trastuzumab-based therapy and before treatment with  Enhertu. Information on FDA-approved tests available at: http://www.fda.gov/CompanionDiagnostics.
• Monitor CBC prior to start of therapy and before each dose, and as clinically indicated.  If neutropenia of Grade 3 (less than 1.0–0.5 × 10⁹ /L) occurs,  hold therapy until resolved to ≤Grade 2, then resume at same dose.  If Grade 4 neutropenia (less than 0.5 × 10⁹ /L) occurs,  hold therapy until resolved to ≤Grade 2, then reduce dose by 1 level. If febrile neutropenia (absolute neutrophil count of <1.0 × 10⁹ /L and temperature >38.3°C or a sustained temperature of ≥38°C for >1 hr), hold therapy until resolved. Reduce dose by 1 level.

Potential Diagnoses

• Deficient knowledge, related to medication regimen (Patient/Family/Teaching) 

Implementation

• Do not substitute fam-traztuzumab deruxtecan for or with trastuzumab or ado-trastuzumab.
• Dose reduction schedule:

  Breast cancer:  Starting dose 5.4 mg/kg. First dose reduction to 4.4 mg/kg. Second reduction to 3.2 mg/kg. If further dose reduction is needed, discontinue therapy. Do not re-escalate dose after dose reduction is made.

  • Gastric Cancer: Starting dose 6.4 mg/kg. First dose reduction to 5.4 mg/kg. Second reduction to 4.4 mg/kg. If further dose reduction is needed, discontinue therapy. Do not re-escalate dose after dose reduction is made.

Patient/Family Teaching

• Explain purpose of therapy to patient. Advise patient to read  Medication Guide  before starting therapy.
• Advise patient to notify health care professional immediately if signs and symptoms of lung problems (cough, trouble breathing or shortness of breath, fever, other new or worsening breathing symptoms [chest tightness, wheezing], infection (fever, chills), or heart problems (new or worsening shortness of breath, coughing, feeling tired, swelling of ankles or legs, irregular heartbeat, sudden weight gain, dizziness or feeling lightheaded, loss of consciousness) occur.
• Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
• Rep:  May cause fetal harm. Advise females of reproductive potential to use effective contraception and avoid breastfeeding during and for at least 7 mo after last dose. Advise males with female partners of reproductive potential to use effective contraception during and for at least 4 mo after last dose. May impair male fertility.

Evaluation/Desired Outcomes

• Regression of breast cancer and metastases.
• Improved survival in gastric or gastroesophageal junction adenocarcinoma.