Understanding the Drug:

• Kadcyla (ado-trastuzumab emtansine) is a monoclonal antibody-drug conjugate used primarily in the treatment of HER2-positive metastatic breast cancer. It combines trastuzumab, a HER2-targeted antitumor antibody, with DM1, a cytotoxic agent, enhancing the delivery of the cytotoxic agent directly to the cancer cells.

Indications:

• Kadcyla is approved for patients who have previously received trastuzumab and taxane, either separately or in combination. Patients should have either received prior therapy for metastatic disease or developed disease recurrence during or within six months of completing adjuvant therapy.

Dosing Strategy:

• Kadcyla is administered via intravenous infusion. The typical dosage is 3.6 mg/kg every 21 days. It is crucial to not substitute Kadcyla for or with trastuzumab.

Administration Tips:

• Infusion reactions can occur; premedication with an antipyretic and antihistamine can mitigate these. The initial infusion should be delivered over 90 minutes and if tolerated without reaction, subsequent infusions can be accelerated to 30 minutes.

Monitoring Requirements:

• Regular monitoring of left ventricular function is required due to potential cardiotoxicity. Liver function tests should also be conducted before each dose since hepatotoxicity is a risk.

Handling and Storage:

• Kadcyla should be handled with care as it is a cytotoxic agent. Pharmacy staff should follow guidelines for handling hazardous drugs. The drug should be stored in a refrigerator and protected from light.

Side Effects Management:

• Common side effects include fatigue, nausea, musculoskeletal pain, and thrombocytopenia. Management involves supportive care and dose adjustments as necessary. Severe side effects necessitate discontinuation or dose modifications.

Use in Special Populations:

• There is limited data on the use of Kadcyla in pregnant or breastfeeding women, and it may cause fetal harm. Women of reproductive potential should be advised to use effective contraception during and for several months after the completion of treatment.

Drug Interactions:

• Careful consideration is needed when combining Kadcyla with other medications. Concomitant use of P-gp inhibitors or strong CYP3A4 inhibitors can increase exposure to DM1, potentially increasing toxicity.

Patient Education:

• Educate patients about the importance of adhering to the treatment schedule and the need to report any side effects. Also, discuss the potential for serious reactions and the importance of regular follow-up appointments for monitoring.