What side effects can Tukysa (tucatinib) cause?
Tukysa’s side effects depend on your dosing schedule and what other cancer medicines you’re taking, but the drug is most associated with gastrointestinal issues, fatigue, and lab abnormalities. Commonly reported effects include diarrhea, nausea, vomiting, decreased appetite, and tiredness/fatigue. It can also cause liver enzyme elevations, so monitoring with blood tests is important.
Because Tukysa is used with trastuzumab (and often with capecitabine), some symptoms may overlap with side effects from those medicines as well.
What are the most common GI side effects?
Patients commonly report stomach and bowel effects such as:
- Diarrhea
- Nausea
- Vomiting
- Decreased appetite
Managing diarrhea early is especially important, since it can lead to dehydration and electrolyte problems if it becomes severe.
What serious side effects should patients watch for?
Tukysa can require prompt attention if you develop signs of serious complications, particularly related to the liver and severe GI toxicity. Seek urgent care if you have symptoms such as:
- Severe or persistent diarrhea (especially if you cannot keep fluids down)
- Signs of dehydration (dizziness, fainting, very low urination)
- Symptoms of liver problems, such as yellowing of the skin/eyes (jaundice), dark urine, severe right-upper-abdominal pain, or marked fatigue
Your oncology team may adjust the dose or pause treatment if these occur.
Why do liver tests matter with Tukysa?
Tukysa can raise liver enzymes, so clinicians typically monitor blood work during treatment. If liver levels rise, your team may reduce the dose, interrupt therapy, or stop it depending on severity.
How do side effects differ when Tukysa is taken with trastuzumab and capecitabine?
When Tukysa is combined with trastuzumab and capecitabine, side effects can come from any of the three drugs. In practice:
- GI side effects like diarrhea can overlap with the other medicines.
- Capecitabine can also contribute to hand-foot (palmar-plantar) skin reactions, which patients may notice alongside Tukysa-related effects.
- Blood-count and fatigue symptoms may also overlap depending on your overall regimen and schedule.
If you’re on a specific combination, your prescriber can tell you which side effects are most likely from each drug in your regimen.
When should you call your doctor during Tukysa treatment?
Contact your oncology team right away if you have:
- Diarrhea that is severe, rapidly worsening, or not controlled with your prescribed anti-diarrheal plan
- Vomiting that prevents you from drinking fluids
- Signs of dehydration
- Yellowing of the skin or eyes, or other symptoms of liver trouble
- Any fever or signs of infection, especially if your blood counts are low from treatment
Are there any drug interactions that affect side effects?
Yes. Tukysa’s metabolism involves liver enzymes, so certain medications can change its levels, which can increase side effects or reduce effectiveness. Tell your team about all medicines and supplements you take, including:
- Seizure medications
- Antibiotics/antifungals
- HIV medicines
- St. John’s wort and other herbal products
What’s the safest way to manage common side effects?
Your oncology team typically gives a plan for:
- Early anti-diarrheal treatment if diarrhea starts
- Hydration guidance
- When to hold or adjust the dose for certain toxicities
- Regular lab monitoring (especially liver enzymes)
Using the treatment plan promptly can prevent mild side effects from becoming severe.
Sources
I don’t have the specific Tukysa prescribing information or clinical-safety table in the materials available to me here, so I can’t cite exact side-effect rates or the full labeled list.
If you paste the Tukysa package insert text (or tell me whether you’re taking it with trastuzumab alone or with capecitabine), I can tailor the side-effect list to your regimen and summarize it accurately.