Medical Oncologist
Alectinib side effects
Muscle Pain and High CPK — on Alectinib: When to Worry
Muscle pain on alectinib is common and usually manageable at home. The question is whether it is ordinary aching or the first sign of serious muscle breakdown. One symptom — dark or brown-coloured urine — means go to hospital today, not tomorrow.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed August 2026
- Usually not dangerous — Most muscle aching on alectinib is mild and does not mean the treatment is harming you.
- CPK is your early warning — Your CPK blood test shows how much muscle strain is happening, often before symptoms become severe.
- Dark urine is the red flag — Brown or red-coloured urine alongside muscle pain can indicate rhabdomyolysis — a serious condition needing emergency care.
- Do not stop without asking — If muscle pain appears, call your team before deciding to skip or stop a dose.
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Muscle pain on alectinib is common and usually mild. The concern rises when it reflects serious muscle breakdown — a condition called rhabdomyolysis — which your CPK blood test can detect early. Dark or brown-coloured urine alongside muscle pain means go to hospital now, not wait for your next appointment.
What can you do at home while you wait to hear from your team?
- Rest the muscles that are sore. Avoid strenuous exercise until you have spoken to your team.
- Drink enough fluids to keep your urine pale yellow — good hydration helps protect your kidneys.
- Note which muscles are affected, when the pain started, and whether it is getting better or worse.
- Write down any other medicines, supplements, or herbal remedies you are taking — some can raise CPK on their own.
- Keep your scheduled blood test appointments. CPK monitoring is part of your routine care on alectinib.
- Ask your team before taking any painkiller. Some common pain medicines can affect the kidneys when CPK is elevated.
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How serious are your muscle symptoms right now?
| Feature | Mild — mention at next visit | Act today — call your team | Go to hospital now |
|---|---|---|---|
| Muscle pain | Dull ache that does not limit daily activity | Worse day on day, or limiting what you can do | So severe you cannot walk or use the limb |
| Urine colour | Normal pale yellow | Darker than usual | Brown, red, or cola-coloured |
| Muscle weakness | None | Some weakness in an arm or leg, getting worse | Cannot walk, lift, or function normally |
| CPK result (from blood test) | Mildly above your lab's normal range | Clearly above normal — your team will advise next steps | Very high — your team will tell you if this applies to you |
| Typically starts | Weeks into alectinib treatment | Can appear at any point during treatment | Can occur at any point — does not become more likely over time |
Did you know?
CPK can rise on alectinib without causing noticeable muscle pain. This is why your team monitors it through scheduled blood tests — the aim is to catch a rising level before it causes a problem, not only after symptoms appear.
Tell your team at every blood test if you have noticed any new aching, even if it seems minor.
Source: Alecensa (alectinib) Prescribing Information, Roche/Genentech
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Common questions
Frequently asked questions
Is muscle pain on alectinib always a sign of serious damage?
No. Mild muscle aching is one of the more common side effects of alectinib and most people who experience it do not develop a serious problem. What your team is watching for is a pattern of worsening pain, a rising CPK level, or the appearance of dark urine. A dull ache that stays the same and does not limit your daily activity is worth mentioning at your next visit, but is not a reason to stop the medicine without asking first.
What does a raised CPK result actually mean?
CPK is an enzyme that leaks from muscle fibres when they are under strain or breaking down. A mildly raised result on alectinib is common and may not cause any symptoms. A significantly raised level means your team will want to see you sooner, check whether you have symptoms, and may adjust your dose. A very high level — especially alongside muscle pain or dark urine — can indicate serious muscle breakdown that can affect the kidneys and needs urgent treatment.
Should I stop taking alectinib if I have muscle pain?
Not without speaking to your oncology team first. Stopping or missing doses on your own can affect how well the treatment controls your cancer. Your team may decide to pause alectinib, reduce the dose, or continue with closer monitoring — that decision depends on how severe the symptoms are and what your CPK level shows. Call your team to describe the pain and they will advise you on what to do with your next dose if needed.
Can I take paracetamol or ibuprofen for the muscle pain?
Paracetamol is generally considered safer in this situation, but ask your team before taking anything. Ibuprofen and other anti-inflammatory medicines can affect kidney function, and if your CPK is already elevated, protecting the kidneys matters. Do not assume a medicine that is safe in other situations is safe now — the threshold changes when muscle breakdown is a possibility. Your team can advise which painkiller is appropriate for your specific situation.
Will my alectinib dose have to change because of a high CPK?
It depends on how high the level is and whether you have symptoms. Many people with mildly elevated CPK continue at the same dose with closer monitoring. For clearly elevated levels alongside symptoms, the prescribing guidance recommends pausing treatment and restarting at a lower dose once the level has settled. Your oncologist will make this decision based on your results and how well the treatment is controlling your cancer — it is not automatic, and many people do not need a dose change at all.