What are the side effects of tucatinib?

Side Effects of Tucatinib

Tucatinib commonly causes diarrhea, nausea, hepatotoxicity (elevated liver enzymes), palmar-plantar erythrodysesthesia syndrome, and fatigue, with diarrhea and elevated aminotransferases being the most frequent grade ≥3 adverse events requiring close monitoring and potential dose modification. 1, 2

Most Common Adverse Events

Gastrointestinal Effects

• Diarrhea: The most prevalent side effect, occurring frequently and can be severe (grade ≥3)
• Nausea and vomiting: Common but typically manageable
• Stomatitis: Reported in clinical practice 3

Hepatotoxicity

• Elevated liver enzymes are particularly important:
  • Alanine aminotransferase (ALT) elevation: 16.5% grade ≥3 4
  • Aspartate aminotransferase (AST) elevation: 16.5% grade ≥3 4
  • These elevations are significantly more common than with control treatments and require regular monitoring 1, 2

Dermatologic Manifestations

• Palmar-plantar erythrodysesthesia syndrome (hand-foot syndrome): Common and can be dose-limiting 2
• Rash: Frequently reported 3
• Nail disorders: Including paronychia, ingrowing nail, onychalgia, onychomadesis, and fingerprint loss 3
• Skin changes: Discoloration, hyperpigmentation, exfoliation, hypertrophy, and blister formation 3
• Telangiectasias: Reported when combined with trastuzumab emtansine, potentially reversible with treatment cessation 5

Hematologic Effects

• Anemia: Reported in clinical use 3
• Platelet count abnormalities: Observed but not explicitly mentioned in original labeling 3

Serious and Less Common Adverse Events

Cardiovascular

• Ejection fraction decreased 3
• Aortic valve incompetence 3

Metabolic/Electrolyte Disturbances

• Dehydration 3
• Hypokalemia 3

Neurological/Neuropsychiatric

• Peripheral neuropathy 3
• Memory impairment 3
• Brain edema 3
• Central nervous system lesions 3
• Hyperesthesia and taste disorders 3
• Emotional disorders 3

Constitutional Symptoms

• Fatigue: Common across studies 2

Age-Related Considerations

In patients ≥65 years, serious adverse reactions occur more frequently (34% vs 24% in younger patients), with diarrhea (9%), vomiting (6%), and nausea (5%) being the most common serious events in this age group 1.

Treatment Discontinuation

• 22.1% of patients discontinued tucatinib due to treatment-emergent adverse events (compared to 11.6% with control) 4
• Grade ≥3 adverse events occurred in 68.8% of tucatinib-treated patients versus 41.2% in controls 4

Critical Monitoring Parameters

Hepatic Function

Monitor liver function tests regularly due to significant risk of transaminase elevation, which represents the most common grade ≥3 laboratory abnormality 1, 4.

Gastrointestinal Toxicity

Implement early intervention strategies for diarrhea management, as this is the most frequent adverse event leading to dose modifications or discontinuation 2.

Dermatologic Assessment

Regular skin and nail examinations are essential, particularly in patients developing hand-foot syndrome or other cutaneous manifestations 3.

Drug Interactions Affecting Toxicity

Tucatinib is both a substrate and inhibitor of multiple drug-metabolizing enzymes:

• Avoid strong CYP2C8 inhibitors (increases tucatinib exposure and toxicity risk) 1
• Avoid strong CYP3A inducers (reduces tucatinib efficacy) 1
• Tucatinib increases exposure to CYP3A and P-glycoprotein substrates, potentially increasing their toxicity 1

Pregnancy and Reproductive Considerations

Tucatinib can cause fetal harm based on animal studies showing embryo-fetal mortality, reduced fetal weight, and fetal abnormalities at clinically relevant exposures 1. Effective contraception is required during treatment and for 1 week after the last dose for both females and males with reproductive partners 1.