Dazublys (Trastuzumab)

What Is Dazublys and What Is It Used For?

Dazublys contains the active substance trastuzumab, a humanised monoclonal antibody produced by recombinant DNA technology. It received European Union marketing authorisation on 30 June 2025 as a biosimilar to the reference medicine Herceptin, which has been used for over two decades in the treatment of HER2-positive cancers. As a biosimilar, Dazublys has undergone comprehensive comparability studies demonstrating that it is highly similar to Herceptin in quality, biological activity, efficacy, and safety.

The HER2 protein (human epidermal growth factor receptor 2) is found on the surface of some cancer cells. When HER2 is overexpressed — a phenomenon observed in approximately 20–30% of primary breast cancers and up to 42.6% of gastric cancers depending on the testing method — it sends signals that drive uncontrolled cell growth and tumour progression. Trastuzumab works by binding with high affinity and specificity to subdomain IV of the extracellular domain of HER2.

By attaching to HER2, Dazublys exerts its anti-tumour effects through several mechanisms. It inhibits ligand-independent HER2 signalling, which prevents cancer cells from receiving growth signals. It also blocks the proteolytic cleavage of HER2's extracellular domain, maintaining the receptor in an inactive state. Perhaps most importantly, trastuzumab is a potent mediator of antibody-dependent cell-mediated cytotoxicity (ADCC), meaning it activates the body's own immune cells to recognise and destroy HER2-overexpressing tumour cells.

Approved Indications

Dazublys is approved for the following clinical uses, consistent with the reference medicine Herceptin:

Early Breast Cancer (HER2-positive): Dazublys is used after surgery and standard chemotherapy (adjuvant setting) for early-stage breast cancer that overexpresses HER2. It can also be used in combination with chemotherapy regimens containing paclitaxel, docetaxel, or carboplatin. The standard treatment duration in early breast cancer is one year or until disease recurrence, whichever occurs first.

Metastatic Breast Cancer (HER2-positive): For patients with advanced or metastatic breast cancer, Dazublys may be used as monotherapy (alone) in patients who have already received at least two prior chemotherapy regimens. It is also used in combination with paclitaxel or docetaxel for patients who have not previously received chemotherapy for metastatic disease, and in combination with aromatase inhibitors for postmenopausal patients with hormone receptor-positive disease.

Metastatic Gastric Cancer (HER2-positive): Dazublys is indicated in combination with cisplatin and either capecitabine or 5-fluorouracil for the treatment of HER2-positive metastatic adenocarcinoma of the stomach or gastro-oesophageal junction in patients who have not received prior anti-cancer treatment for their metastatic disease.

What Should You Know Before Taking Dazublys?

Contraindications

Dazublys must not be used in patients who have a known hypersensitivity to trastuzumab, to murine (mouse-derived) proteins, or to any of the excipients in the formulation. Since trastuzumab is a humanised monoclonal antibody originally derived from a murine antibody, patients with documented allergies to murine proteins are at higher risk of severe hypersensitivity reactions.

Dazublys is also contraindicated in patients who have severe dyspnoea (difficulty breathing) at rest due to complications of advanced malignancy, or who require supplementary oxygen therapy. These patients are at significantly increased risk of fatal infusion-related pulmonary events.

Warnings and Precautions

Cardiotoxicity: The most clinically significant risk associated with trastuzumab therapy is cardiotoxicity. Trastuzumab can cause left ventricular dysfunction, manifesting as decreased left ventricular ejection fraction (LVEF) and, in some cases, symptomatic congestive heart failure. The risk is particularly elevated in patients who have previously received or are concurrently receiving anthracycline-containing chemotherapy (such as doxorubicin or epirubicin), as these agents are independently cardiotoxic.

Before starting Dazublys, all patients must undergo a thorough cardiac assessment including a medical history review, physical examination, electrocardiogram (ECG), and echocardiogram or MUGA scan to determine baseline LVEF. During treatment, cardiac function should be monitored every three months, and after treatment completion, monitoring should continue every six months for at least 24 months from the last dose.

If LVEF drops by 10 percentage points or more from baseline and falls below 50%, treatment should be suspended and a repeat assessment performed within approximately three weeks. If LVEF does not recover, or if symptomatic heart failure develops, serious consideration should be given to discontinuing Dazublys unless the benefits clearly outweigh the risks for the individual patient.

Infusion-Related Reactions: Infusion-related reactions are common with trastuzumab therapy and may include fever, chills, nausea, wheezing, bronchospasm, tachycardia, hypotension, dyspnoea, rash, and fatigue. More serious reactions including anaphylaxis, angioedema, and respiratory distress have been reported, though they are uncommon. Most reactions occur during or within 2.5 hours of the first infusion. Pre-medication with analgesics and antihistamines may reduce the risk.

Patients should be observed for at least 6 hours after the first infusion and for at least 2 hours after subsequent infusions to monitor for delayed reactions. Healthcare facilities administering Dazublys must have resuscitation equipment readily available.

Pulmonary Events: Serious pulmonary adverse events have been reported with trastuzumab, including interstitial lung disease, acute respiratory distress syndrome, pneumonia, pneumonitis, pleural effusion, and pulmonary oedema. The risk of severe pulmonary events is increased in patients who are concurrently receiving taxanes, gemcitabine, vinorelbine, or radiation therapy. Patients who develop dyspnoea at rest should be evaluated promptly.

Pregnancy and Breastfeeding

Pregnancy: Dazublys should be avoided during pregnancy unless the potential benefit for the mother clearly outweighs the potential risk to the foetus. Post-marketing surveillance with the reference medicine trastuzumab has documented cases of foetal renal growth and function impairment associated with oligohydramnios (reduced amniotic fluid), some of which were associated with fatal pulmonary hypoplasia of the newborn. While animal reproductive studies at doses significantly exceeding the human therapeutic dose did not reveal evidence of impaired fertility or direct foetal harm, the clinical experience raises significant concern.

Women of childbearing potential must use effective contraception during treatment with Dazublys and for at least 7 months after the last dose. If a patient becomes pregnant during treatment, close monitoring of the pregnancy is essential, particularly regarding amniotic fluid volume and foetal kidney development.

Breastfeeding: It is not known whether trastuzumab is excreted in human milk. However, as human immunoglobulin G (IgG) is secreted into breast milk, and animal studies have demonstrated transfer of trastuzumab into milk, women should not breastfeed during treatment with Dazublys and for at least 7 months after the last dose.

Fertility: No specific studies have evaluated the effect of trastuzumab on human fertility. No adverse fertility effects were observed in animal studies.

How Does Dazublys Interact with Other Drugs?

No formal drug interaction studies have been performed with trastuzumab. In clinical trials, clinically significant pharmacokinetic interactions between trastuzumab and concurrently administered chemotherapy agents were not observed. However, the clinical significance of potential pharmacodynamic interactions, particularly regarding cardiac risk, should not be underestimated.

Trastuzumab does not appear to alter the pharmacokinetics of paclitaxel, doxorubicin, docetaxel, carboplatin, or capecitabine when used in combination regimens. Similarly, the pharmacokinetics of trastuzumab are not significantly altered by concurrent administration of docetaxel, paclitaxel, or anastrozole. One finding of potential interest is that exposure to a doxorubicin metabolite (doxorubicinol, D7D) may be elevated when doxorubicin is administered alongside trastuzumab, though the clinical significance of this observation remains unclear.

Major Interactions

Other Interactions of Note

What Is the Correct Dosage of Dazublys?

Dazublys must be initiated by a physician experienced in the administration of cytotoxic chemotherapy and should only be administered in a healthcare setting equipped to manage potential infusion-related reactions, including anaphylaxis. The drug must never be administered as an intravenous push or bolus injection.

Adults

Children

There is no relevant paediatric use of Dazublys. Trastuzumab is not indicated for use in children or adolescents under 18 years of age, as HER2-positive breast cancer and gastric cancer are almost exclusively adult diseases. No paediatric clinical studies have been conducted.

Elderly

Population pharmacokinetic analyses have shown that age does not significantly affect the disposition of trastuzumab. No specific dose adjustments are required for elderly patients. However, as the risk of cardiac dysfunction increases with age, careful cardiac monitoring is particularly important in older patients, especially those with pre-existing cardiovascular conditions or prior anthracycline exposure.

Missed Dose

If a scheduled dose of Dazublys is missed by one week or less, the usual maintenance dose should be administered as soon as possible without waiting for the next scheduled cycle. Subsequent maintenance doses should then resume at the originally planned intervals (7 or 21 days from the make-up dose).

If a dose is missed by more than one week, a re-loading dose should be administered over approximately 90 minutes, followed by the usual maintenance schedule. Patients should be monitored for infusion-related reactions as with the initial loading dose.

Overdose

There is no experience with overdose in human clinical trials. Single doses exceeding 10 mg/kg have not been tested in clinical studies. In the event of an overdose, patients should be closely monitored for signs and symptoms of adverse reactions, particularly infusion-related events and cardiac effects. Treatment is supportive, as there is no specific antidote for trastuzumab.

What Are the Side Effects of Dazublys?

As a biosimilar medicine, the safety profile of Dazublys is comparable to that of the reference medicine Herceptin. The following side effects have been documented in clinical trials and post-marketing experience with trastuzumab. The frequency categories follow the standard convention: very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), and rare (≥1/10,000 to <1/1,000).

It is important to recognise that many patients receiving trastuzumab are also receiving concurrent chemotherapy, which contributes to the overall adverse event profile. The attribution of individual side effects to trastuzumab versus chemotherapy is not always straightforward, and the frequencies reported below reflect the combination experience in clinical trials.

How Should You Store Dazublys?

Proper storage of Dazublys is essential to maintain the integrity and potency of this biological medicine. As a protein-based product, trastuzumab is sensitive to temperature extremes and physical stress.

Unopened vials: Dazublys vials must be stored in a refrigerator at 2–8°C (36–46°F). The shelf life of unopened vials is 4 years when stored under these conditions. Vials should be kept in their original packaging to protect from light. Do not freeze.

Reconstituted solution: After reconstitution with 7.2 mL of sterile water for injection (producing a solution containing approximately 21 mg/mL trastuzumab), the reconstituted solution has demonstrated chemical and physical stability for up to 48 hours when stored at 2–8°C. Do not freeze the reconstituted solution. From a microbiological safety perspective, the product should be used immediately after reconstitution unless prepared under validated aseptic conditions.

Diluted infusion solution: After dilution in 0.9% sodium chloride infusion bags, the solution is physically and chemically stable for up to 30 days at 2–8°C and for up to 24 hours at temperatures not exceeding 30°C (86°F). From a microbiological standpoint, the diluted solution should be used immediately or, if not used immediately, stored at 2–8°C for no more than 24 hours unless reconstituted and diluted under controlled and validated aseptic conditions.

Dazublys must not be mixed with or diluted using glucose (dextrose) solutions, as these are incompatible and may cause protein aggregation. Only 0.9% sodium chloride solution should be used as the infusion diluent. Do not use polyethylene bags for the infusion unless compatibility has been confirmed. Keep out of the sight and reach of children.

What Does Dazublys Contain?

Active substance: Each vial contains 150 mg of trastuzumab, a humanised IgG1 monoclonal antibody produced by recombinant DNA technology in Chinese hamster ovary (CHO) cells. Trastuzumab specifically targets the extracellular domain of the human epidermal growth factor receptor 2 (HER2). After reconstitution with 7.2 mL of sterile water for injection, the resulting solution contains approximately 21 mg/mL of trastuzumab.

Excipients: The powder for concentrate for solution for infusion also contains the following inactive ingredients:

• Histidine hydrochloride monohydrate — buffer component that maintains the pH of the solution within the optimal range for trastuzumab stability
• Histidine — buffer component working alongside histidine hydrochloride to maintain solution pH
• α,α-Trehalose dihydrate — a disaccharide sugar used as a lyoprotectant (stabiliser during the freeze-drying process) and cryoprotectant that helps preserve the protein structure
• Polysorbate 20 (E432) — a non-ionic surfactant (0.6 mg per vial) that prevents protein aggregation and helps maintain solution clarity. This excipient is well-established in parenteral formulations

The formulation does not contain preservatives, and each vial is intended for single use only. Any unused solution remaining after preparation of the infusion should be discarded in accordance with local requirements for the disposal of cytotoxic medicines.

Dazublys is presented as a white to pale yellow lyophilised (freeze-dried) powder. After reconstitution, the solution should be clear to slightly opalescent and colourless to pale yellow. Do not use the solution if it contains visible particulate matter or if it is discoloured.