Trastuzumab

Introduction Overview

Generic Name

trastuzumab

Brand Name

Herceptin

Dosage Form

Intravenous infusion (single-dose vial and multi-dose vial)

Drug Class

HER2 inhibitors

Pharmacokinetics

Absorption: Trastuzumab is administered exclusively by intravenous infusion, bypassing the gastrointestinal tract, thus ensuring complete bioavailability. Absorption via other routes has not been studied and is not clinically relevant due to its monoclonal antibody nature and large molecular size. Distribution: After intravenous administration, trastuzumab exhibits a volume of distribution close to plasma volume, reflecting limited extravascular distribution typical of monoclonal antibodies. It binds specifically with high affinity to the extracellular domain IV of the HER2 receptor expressed on tumor cells, leading to selective tumor targeting. Trastuzumab does not extensively penetrate into the cerebrospinal fluid or across the blood-brain barrier. Metabolism: As a recombinant humanized monoclonal antibody, trastuzumab is catabolized proteolytically into small peptides and amino acids via reticuloendothelial and cellular processes and is not metabolized by the cytochrome P450 enzyme system. The metabolism is similar to endogenous IgG antibodies with no formation of active metabolites. Elimination: The systemic clearance of trastuzumab follows a nonlinear pharmacokinetic profile, reflecting target-mediated drug disposition. The terminal elimination half-life is approximately 28.5 days after a loading dose, allowing administration intervals of one to three weeks. Clearance can vary based on tumor burden and patient factors, with antibody clearance increasing when HER2-expressing tumor cells are abundant. Trastuzumab is eliminated primarily by proteolytic catabolism throughout the body and is not renally excreted.

Dosage Forms

Available Dosage Forms: Herceptin is supplied as a sterile, preservative-free lyophilized powder for injection in single-dose and multi-dose vials intended for intravenous infusion. The common vial strengths include:
- Single-Dose Vial: 150 mg trastuzumab
- Multi-Dose Vial: 420 mg trastuzumab
The medication must be reconstituted and further diluted in an appropriate intravenous infusion solution prior to administration.
Dosages for Adults and Adolescents:
- Metastatic Breast Cancer: Initial dose 4 mg/kg IV infusion over 90 minutes; subsequent doses 2 mg/kg IV infusion over 30 minutes weekly until disease progression.
- Adjuvant Breast Cancer:
1) Concurrent with paclitaxel or docetaxel-based chemotherapy: Initial dose 4 mg/kg IV infusion over 90 minutes; subsequent weekly doses 2 mg/kg IV over 30 minutes for 12 or 18 weeks, followed by 6 mg/kg IV every 3 weeks for a total duration of 52 weeks.
2) As a single agent following chemotherapy: Initial dose 8 mg/kg IV over 90 minutes, then 6 mg/kg IV every 3 weeks for 17 doses (52 weeks total).
- Metastatic Gastric or Gastroesophageal Adenocarcinoma: Initial dose 8 mg/kg IV over 90 minutes; maintenance 6 mg/kg IV every 3 weeks until disease progression, in combination with cisplatin and capecitabine or 5-fluorouracil.
Specific Patient Populations:
- Treatment regimens and dosage adjustments may be tailored based on patient clinical condition, cardiac function, and co-administration of chemotherapy agents.
- Because trastuzumab can cause cardiotoxicity, cardiac monitoring is essential before and during treatment.
- Use in pediatric populations has not been established.
- Pregnancy is contraindicated; effective contraception must be employed during treatment and for at least 7 months post-therapy.
- No specific dosing modifications are provided for renal or hepatic impairment due to the antibody degradation pathway.

Mechanism Of Action

Trastuzumab is a recombinant humanized monoclonal antibody directed against the extracellular domain IV of the human epidermal growth factor receptor 2 (HER2/neu), a transmembrane tyrosine kinase receptor overexpressed in certain malignancies, notably HER2-positive breast and gastric cancers. By binding to HER2, trastuzumab inhibits ligand-independent HER2 signaling pathways that promote cellular proliferation and survival. This blockade results in the inhibition of downstream signaling cascades such as the PI3K/AKT and MAPK pathways, leading to reduced tumor cell growth and induction of apoptosis.
In addition to receptor blockade, trastuzumab induces antibody-dependent cellular cytotoxicity (ADCC) by recruiting immune effector cells, such as natural killer cells and macrophages, which identify and lyse HER2-overexpressing tumor cells. This immune-mediated mechanism substantially contributes to its antitumor efficacy. Furthermore, trastuzumab promotes HER2 receptor internalization and degradation, decreasing receptor density on the cell surface, further dampening proliferative signals.
Clinical studies correlate trastuzumab’s mechanism with significant survival benefits in HER2-positive breast cancer patients, especially when combined with chemotherapeutic agents like paclitaxel or docetaxel. Comparative mechanisms with other HER2-targeted therapies, such as pertuzumab, which binds distinct HER2 domains, underscore trastuzumab’s unique contribution in monotherapy and combination regimens.
Ongoing research elucidates resistance mechanisms to trastuzumab, including HER2 receptor mutations and alternative signaling pathway activation, which inform development of next-generation HER2 inhibitors and antibody-drug conjugates to improve clinical outcomes.

Pharmacological Actions

Selective inhibition of HER2 receptor tyrosine kinase signaling in HER2-overexpressing cells
Induction of antibody-dependent cellular cytotoxicity (ADCC) against tumor cells
Promotion of HER2 receptor internalization and degradation, reducing oncogenic signaling
Synergistic antitumor activity when combined with chemotherapeutic agents such as paclitaxel and docetaxel
Modulation of downstream intracellular signaling cascades including PI3K/AKT and MAPK pathways leading to cell cycle arrest and apoptosis
Immunomodulatory effects by enhancing recognition of tumor cells by the immune system
Targets metastatic and primary HER2-positive tumors, impairing tumor growth and progression
Long half-life supporting intermittent dosing schedules to maintain effective plasma concentrations

Therapeutic Or Clinical Uses

Treatment of HER2-positive metastatic breast cancer as monotherapy or combined with chemotherapy
Adjuvant treatment of HER2-positive early breast cancer following surgery and chemotherapy
First-line therapy for metastatic gastric or gastroesophageal junction adenocarcinoma in combination with chemotherapy
Management of HER2-positive breast cancer to reduce recurrence risk and improve overall survival
Used in combination regimens such as with paclitaxel, docetaxel, carboplatin, cisplatin, capecitabine, or 5-fluorouracil
Treatment in patients with HER2-overexpressing tumors identified by immunohistochemistry or fluorescence in situ hybridization
Applicable in patients with both newly diagnosed and relapsed HER2-positive cancers
Potential use in combination with other targeted therapies as part of multimodal cancer treatment strategies

Side Or Adverse Effects

Cardiotoxicity including congestive heart failure and decreased left ventricular ejection fraction
Infusion-related reactions such as fever, chills, nausea, dizziness, headache, and hypotension
Gastrointestinal disturbances including nausea and diarrhea
Hematological abnormalities, notably neutropenia and other low blood cell counts
Fatigue and asthenia
Rash and skin reactions
Mouth sores or stomatitis
Respiratory symptoms including cough and increased risk of infections
Altered taste sensation
Potential for allergic or hypersensitivity reactions including anaphylaxis
Tumor lysis syndrome with symptoms such as muscle cramps, nausea, and arrhythmias
Rare neurological symptoms like headache and visual disturbances
Musculoskeletal pain and increasing discomfort with prolonged therapy
Weight loss and anorexia
Cold-like symptoms such as nasal congestion and sore throat

Precautions

Screen cardiac function prior to initiation and monitor regularly during treatment to detect early signs of cardiotoxicity
Avoid usage in pregnant women due to teratogenicity and fetal risk; mandate effective contraception during and 7 months post-treatment
Inform patients about the potential for infusion reactions and ensure experienced personnel and emergency interventions are available
Delay or discontinue therapy if severe cardiac dysfunction, infusion reactions, or severe adverse effects occur
Screen for hypersensitivity or allergic reaction history before administration
Monitor complete blood counts periodically to detect hematologic toxicities
Use caution when combining with other cardiotoxic chemotherapeutic agents such as anthracyclines
Perform pregnancy testing in women of childbearing potential before initiation
Advise patients against breastfeeding while receiving trastuzumab and for at least 7 months after the final dose
Monitor for signs of infection or immunosuppression due to neutropenia
Adjust or withhold doses based on adverse event severity and patient tolerance
Educate patients on symptoms indicating urgent medical evaluation, such as shortness of breath and chest pain
Utilize only under supervision of oncology professionals experienced in monoclonal antibody therapies
Maintain vigilance for long-term cardiac effects through extended post-treatment follow-up
Instruct patients to report any new symptoms promptly to healthcare providers

Warnings

Contraindicated during pregnancy due to risk of fetal harm or death; use reliable contraception
Can cause severe or fatal cardiotoxicity, particularly in patients with pre-existing cardiac disease or those receiving concurrent cardiotoxic agents
Potential for serious infusion reactions including anaphylaxis and cytokine release syndrome
May cause fetal harm when administered to pregnant women; enrollment in pregnancy registries recommended if exposure occurs
Monitor heart function before, during, and for up to 2 years after treatment completion due to risk of delayed cardiac effects
Premedication or slowing infusion rate may be necessary during initial administrations to reduce infusion-related reactions
Not recommended for use in patients with known hypersensitivity to trastuzumab or its components
Discontinue if severe infusion reactions or life-threatening cardiac adverse effects occur
Risk of immunogenicity and antibody formation exists but clinically significant events are rare
Avoid concomitant use with anthracyclines unless under strict cardiac monitoring
Use caution in patients with pulmonary or respiratory disorders since serious pulmonary toxicity has been reported
Therapy may be delayed or discontinued depending on severity of adverse effects impacting patient safety
Awareness of potential for tumor lysis syndrome necessitates monitoring in high tumor burden situations
Breastfeeding contraindicated due to unknown excretion in human milk and potential adverse effects on infant
Patients should be informed of potential risks prior to initiation

Contraindication

Known hypersensitivity to trastuzumab or any component of the formulation
Pregnancy due to the potential for fetal toxicity and death
Patients with severe cardiac dysfunction or recent myocardial infarction not adequately stabilized
Concurrent use with anthracyclines without appropriate cardiac monitoring
Use in patients with active serious infections or compromised immune status without medical clearance
Patients with uncontrolled severe infusion-related reactions to trastuzumab
Known hypersensitivity to other monoclonal antibodies potentially cross-reactive
Severe hepatic impairment not studied or recommended
Use in pediatric populations not established and thus contraindicated outside clinical trials
Breastfeeding during treatment and for 7 months afterwards due to potential infant exposure
Patients with systemic hypersensitivity reactions previously to monoclonal antibody therapies
Severe pulmonary conditions that would exacerbate potential pulmonary toxicity with trastuzumab
Conditions where immunosuppression would pose unacceptable risks
Uncorrected electrolyte imbalances associated with tumor lysis syndrome risk
Any other contraindications listed by specific institutional protocols based on emerging evidence

Drug Interactions

Concurrent administration with anthracyclines (e.g., doxorubicin, daunorubicin, epirubicin, idarubicin) increases risk of cardiotoxicity
Potential additive cardiac dysfunction when combined with other HER2-targeted agents or cardiotoxic drugs
No significant cytochrome P450 metabolism interactions due to monoclonal antibody nature
Possible interactions with chemotherapeutic agents that impact immune function or affect hematologic parameters
Trastuzumab may potentiate the effects of other immunomodulating therapies increasing risk of immune-related adverse effects
Coadministration with agents causing QT prolongation requires cardiac monitoring
Interaction data limited with some supportive care medications; clinical monitoring recommended
Potential interference with imaging studies that utilize HER2 target or related diagnostics
Live vaccines should be avoided concomitantly due to immune system modulation
Anticancer therapies that impair renal or hepatic function may alter tolerance to trastuzumab
Herbal supplements and over-the-counter drugs should be disclosed to prescriber to evaluate unknown interactions
Prophylactic corticosteroids may be used to mitigate infusion reactions but may influence immune-mediated efficacy
No formal drug interaction with vitamins, though clinical caution advised when polypharmacy is present
Trastuzumab has no known direct interaction with anticoagulants but bleeding risk assessment warranted due to therapy-associated thrombocytopenia
Therapies affecting heart rate and rhythm may compound trastuzumab cardiotoxic potential

Preparations Of The Drug

Herceptin provided as a sterile, preservative-free lyophilized powder in single-dose vials (150 mg trastuzumab)
Available in multi-dose vials containing 420 mg trastuzumab for intravenous infusion preparation
Requires reconstitution with sterile water and subsequent dilution in an appropriate intravenous infusion solution such as 0.9% sodium chloride
Administered as an intravenous infusion over variable durations: initial dose typically infused over 90 minutes, subsequent doses over 30 to 90 minutes depending on regimen and tolerance
Stored refrigerated and protected from light prior to reconstitution
Preparation requires aseptic technique due to lack of preservative and biological nature
Biosimilar preparations available with similar formulations including Trazimera, Hercessi, Herzuma, Kanjinti, Ogivri, and Ontruzant
Each biosimilar available in matching 150 mg single-dose and 420 mg multi-dose vial presentations
Biosimilars can be substituted based on prescriber specification and pharmacy law
No oral formulations available, reflecting characteristics of monoclonal antibodies
Intravenous infusion necessitates administration by qualified healthcare professionals in a clinical setting
Dosing vials designed to minimize waste and support flexible dosing based on patient weight and regimen
Instructions provide for dilution stability timeframes post-preparation to avoid microbial contamination
Not recommended for intramuscular, subcutaneous, or other non-intravenous routes
Each preparation must be matched to patient-specific dosing with careful calculation