Selpercatinib (Retevmo and Retsevmo)

Medicine at a glance

Selpercatinib is a targeted cancer medicine taken by mouth. Verified brands include Retevmo and Retsevmo. It blocks a growth signal called RET in cancers with a suitable RET gene change. A laboratory result, your diagnosis and your overall health help the oncologist decide whether it is appropriate. A positive test does not guarantee that treatment will work.

Capsules and tablets exist, with important differences in what can be prepared for someone who cannot swallow. Most patients take two doses daily; some younger children take three. Treatment is usually continuous, with no routine week off, until the cancer progresses or side effects make further treatment unsuitable. Only your team should change this plan.

This guide explains the medicine and practical safety measures. Read it alongside your own prescription, product leaflet and hospital instructions. Brand recognition does not establish local availability. Regional instructions differ, particularly for missed doses, some interactions and tablet dispersion.

What selpercatinib is and how it works

RET is a protein involved in messages that tell cells when to grow. A mutation changes the instructions for that protein; a fusion joins part of the RET gene to another gene. Certain changes leave RET sending inappropriate growth signals. Selpercatinib is a tyrosine kinase inhibitor, a medicine that interferes with this signalling activity. Blocking the signal can slow or control a cancer that depends on it.

It is not conventional chemotherapy or a checkpoint immunotherapy. However, targeting a particular signal does not spare every healthy tissue. Blood pressure, liver function, heart rhythm and other body systems can be affected. Treatment therefore needs monitoring even when you feel well. The amount of benefit and its duration differ between people.

How the team decides whether it is suitable

The oncologist checks the exact RET result using an appropriately validated test and interprets whether the mutation or fusion fits your cancer and treatment setting. The diagnosis, previous treatment, other available options, symptoms and applicable prescribing information also matter. Not every reported gene change is a reason to use selpercatinib.

Some children from age two can receive it in selected circumstances under a specialist team. Younger children need a dose calculated from body surface area, which uses height and weight; the smallest supported size differs between US and European guidance. Do not calculate a child's dose from an adult prescription or another child's schedule. Treatment below age two is not established.

Severe liver impairment can require a lower starting dose. End-stage kidney disease and dialysis have limited dosing evidence. A previous reaction to selpercatinib or an ingredient must be disclosed; European information lists ingredient hypersensitivity as a contraindication. Uncontrolled blood pressure must be addressed before treatment starts.

Before treatment starts

Tell the team about liver or kidney disease, lung problems, bleeding, fainting, abnormal heart rhythms, heart failure, thyroid disease and planned surgery. Mention previous immunotherapy, because hypersensitivity reactions have been reported particularly in some patients previously exposed to checkpoint treatment. Bring every medicine and supplement, including heartburn remedies and medicines used only occasionally.

Baseline checks include liver tests, blood pressure, blood counts, kidney function, electrolytes and thyroid function. Electrolytes are salts such as potassium, magnesium and calcium that help nerves, muscles and the heart work normally. An ECG records the heart's electrical activity and helps assess a rhythm risk called QT prolongation. Abnormal salts or thyroid function may need correction. A pregnancy test is required when relevant.

For a child, the team also considers growth and bone development. Before the first dose, obtain a clear schedule, instructions for missed or vomited doses, a plan for side effects and the hospital's urgent advice details. Ask the pharmacist to check the exact formulation if swallowing is difficult.

How treatment is taken

Dose and daily routine

For adults and adolescents aged twelve or over, usual starting doses are 120 mg twice daily below 50 kg body weight and 160 mg twice daily at 50 kg or above. These are examples from prescribing information, not instructions to alter your dose. Side effects, liver impairment or interactions can require a different prescription. Children aged two to under twelve follow their own size-based plan.

Take doses at approximately the same times each day. Capsules contain 40 or 80 mg; tablets contain 40, 80, 120 or 160 mg. Check both the strength and number of units whenever the prescription changes. Swallow capsules whole without opening them. Swallow tablets whole without crushing, chewing or splitting, except when a specifically supported dispersion has been prescribed.

Food and heartburn medicines

Food is normally optional. If a proton pump inhibitor such as omeprazole is essential, take selpercatinib with food. For an H2 blocker such as famotidine, take selpercatinib at least two hours before or ten hours after that medicine. US guidance also separates a local antacid by at least two hours before or after selpercatinib. These remedies can affect absorption; ask the pharmacist to write the actual daily timetable. US information advises avoiding them where possible rather than adding them without review.

Missed doses and vomiting

US Retevmo instructions allow a missed dose only when more than six hours remain before the next scheduled dose. If six hours or less remain, skip it. European Retsevmo instructions say to skip a forgotten dose and take the next one at its usual time. Follow the instructions for your supplied product and prescribed schedule, especially for a child taking three doses daily. Never double a dose.

If you vomit after a dose, do not repeat it. Take the next prescribed dose at the normal time. Contact the team if vomiting continues or you cannot keep fluids down.

If swallowing is difficult

Current US instructions permit a dispersion made only from Retevmo 40 mg tablets. Neither opened capsules nor crushed higher-strength tablets substitute for this method. Have the pharmacist demonstrate the method first. For swallowing, the prescribed one to four 40 mg tablets are dispersed in 15 mL of room-temperature or chilled water or 100% carrot puree, with intermittent stirring for about seven to ten minutes. Take the entire mixture immediately, then add 15 mL water to the same container, swirl or stir, and drink all of this rinse immediately to collect the remaining medicine. Discard any unused dispersion after two hours.

Feeding tubes require a different water-only preparation, specified tube materials and sizes, an enteral syringe and rinses. Have the pharmacist demonstrate the complete method for the actual tube. The current European tablet information instructs whole-tablet swallowing, including use of several smaller tablets where appropriate; it does not provide this US dispersion method. Arrange a product-specific plan rather than improvising.

Storage and handling

Keep medicine securely away from children in its labelled packaging. US storage is 20–25°C (68–77°F), with specified brief temperature excursions; European products require no special storage conditions. Follow the supplied leaflet and avoid leaving medicine in a hot car. Do not swallow a bottle's moisture-absorbing insert. Return unwanted medicine through the pharmacy. If too much is taken, seek medical advice immediately, even without symptoms.

Monitoring and checking whether treatment is working

Liver enzymes are checked before treatment and every two weeks for the first three months. US guidance then continues monthly checks; European guidance specifies monthly checks for the next three months and subsequently as clinically indicated. Abnormal results require closer assessment and sometimes interruption or dose reduction.

Blood pressure needs regular checks. US guidance specifies a check after one week and at least monthly thereafter. European ECG and electrolyte monitoring is specified after one week and at least monthly for the first six months, then according to clinical need. US ECG monitoring is adjusted to risk, interacting medicines and symptoms. Your team may increase testing during diarrhoea or vomiting.

Blood counts, kidney function and thyroid tests are reviewed during treatment. Selpercatinib can raise measured creatinine by affecting its handling in the kidney; the team may use another marker to clarify kidney function. This does not mean that every abnormal result is harmless—dehydration or genuine kidney injury still needs assessment.

Scans and clinical examinations assess cancer control. A treatment hold for toxicity is a safety measure, not proof that the medicine has failed. Keep a record of doses, blood-pressure readings if requested, symptoms and any changes to other medicines.

Common side effects and practical management

Bowel changes and nausea

Diarrhoea, constipation, abdominal discomfort, nausea and vomiting can occur. Take prescribed symptom medicines as directed and replace lost fluids within any fluid limit your team has set. Report persistent diarrhoea early, particularly with dizziness, reduced urine, fever or difficulty drinking. Blood in the stool or severe abdominal pain requires urgent assessment. Do not repeatedly increase antidiarrhoeal or laxative doses without a plan.

Small portions may be easier when you feel sick. If eating becomes difficult, discuss dietetic support rather than relying on supplements that could interact. Constipation with vomiting, swelling of the abdomen or inability to pass wind needs prompt advice.

Dry mouth and skin symptoms

A dry mouth can make eating and speaking uncomfortable. Take small sips, choose moist foods and maintain gentle dental care; ask about saliva substitutes if needed. Report sores that prevent drinking or possible infection. Mild rash may respond to prescribed skin care, but a rash accompanied by fever, pain, blistering or mucosal sores belongs in the urgent category below.

Tiredness and pain with swelling

Fatigue, headache and muscle or joint discomfort are reported. Balance activity with rest, and check painkillers before taking them because bleeding, liver function and interactions affect the choice. New or worsening fatigue may reflect anaemia or thyroid changes and should not simply be endured.

Fluid retention can swell the limbs or face. Report new swelling, rapid weight gain, abdominal enlargement or worsening breathlessness. Fluid can occasionally collect around the lungs or in the abdomen, including milky lymphatic fluid called chyle. These symptoms need assessment rather than automatic attribution to ordinary ankle swelling.

Blood counts and infection

Blood-cell counts can fall. Low white-cell counts increase infection risk, low red cells cause anaemia, and low platelets can contribute to bruising or bleeding. Report infection symptoms promptly. Bleeding can also occur for reasons other than a low platelet count, so a recent normal result is not a reason to ignore it.

Important side effects

Liver injury

Liver-test changes are common and sometimes become serious. Contact the team immediately for yellow eyes or skin, dark urine, upper abdominal pain, marked loss of appetite, unusual sleepiness or unexplained bruising. Blood tests may detect injury before symptoms. Significant abnormalities require a treatment hold and monitoring; any restart and gradual dose adjustment are specialist decisions.

Lung inflammation

Selpercatinib can cause interstitial lung disease or pneumonitis, an inflammation within the lungs that can be life-threatening. New or worsening cough, breathlessness or fever needs urgent assessment before another dose. Treatment is withheld while suspected drug-related inflammation is investigated. Severe confirmed disease or recurrent pneumonitis requires permanent discontinuation; selected less severe cases may restart at a lower dose after recovery under specialist supervision.

Blood pressure and heart rhythm

High blood pressure may cause no symptoms. Take prescribed blood-pressure treatment and report readings outside your agreed limits. Severe headache, confusion, chest pain or severe breathlessness needs emergency assessment.

QT prolongation changes the time the heart takes to electrically reset between beats and can lead to dangerous rhythms. Palpitations, dizziness or fainting need urgent help; collapse is an emergency. Diarrhoea-related salt loss and some anti-sickness, antibiotic or heart medicines can increase this risk. Dose interruption, reduction or permanent stopping may be required.

Bleeding

Report repeated nosebleeds, unusual bruises, blood in urine or unusually heavy vaginal bleeding. Vomiting blood, coughing blood, black tarry stools, uncontrolled bleeding or sudden neurological symptoms need emergency assessment. US guidance permanently stops treatment for severe or life-threatening haemorrhage; European guidance also permits a carefully supervised reduced-dose restart after some severe events, but permanently stops life-threatening or recurrent severe bleeding. Do not restart yourself.

Hypersensitivity and severe skin reactions

Fever with rash and muscle or joint pain can indicate a systemic hypersensitivity reaction. Blood tests may show liver or platelet changes. Seek immediate advice and do not take another dose until assessed. Treatment is held and steroids may be used; any supervised restart follows a reduced-dose escalation plan. Recurrent hypersensitivity requires permanent stopping according to label warnings.

A painful spreading rash, blisters, peeling skin, or sores involving the mouth, eyes or genitals may indicate a severe reaction such as Stevens–Johnson syndrome. Stop taking selpercatinib and obtain emergency assessment. Confirmed severe skin reactions require permanent discontinuation; do not attempt the ordinary hypersensitivity restart plan.

Thyroid changes and other important risks

Low thyroid hormone can cause feeling cold, constipation, weight gain and increasing tiredness. Replacement treatment may need adjustment; sometimes levothyroxine alone is insufficient because selpercatinib affects conversion to another active thyroid hormone. Do not adjust thyroid tablets yourself.

Tumour lysis syndrome occurs when rapid cancer-cell breakdown disturbs salts and kidney function. Higher-risk patients may need extra monitoring, hydration and preventive medicines. Reduced urine, marked weakness, muscle cramps, vomiting, confusion or palpitations need urgent assessment; seizures or collapse are emergencies.

Children need growth-plate monitoring. A new limp, even without pain, or hip or knee pain can signal displacement at the top of the thigh bone. Contact the paediatric team promptly; do not assume it is normal growing pain.

Other medicines supplements and vaccinations

Selpercatinib interacts with medicines affecting a liver enzyme called CYP3A. Examples include some antifungals, antibiotics, antiviral treatments, seizure medicines and St John's wort. US guidance avoids strong and moderate inhibitors and inducers where possible; essential inhibitors require a prescribed dose reduction and closer ECG checks. European instructions explicitly require reduction with strong inhibitors and avoidance of strong inducers. The pharmacist must check the actual combination.

Selpercatinib can also increase exposure to other medicines, including certain cholesterol medicines, sedatives, diabetes medicines, anticoagulants and digoxin. Interactions involving transport proteins matter as well as liver enzymes. Separating these medicines by a few hours does not necessarily prevent the interaction. Remember the distinct acid-reducing medicine timetable described above.

Review vaccines with the team. Non-live vaccines may be appropriate; live vaccines need assessment of immune function and other treatments. Do not assume a fixed twelve-month restriction applies to every person taking selpercatinib. Seek travel-vaccine advice early.

Everyday life during treatment

Plan work and travel around blood tests and medicine supplies. Carry a current treatment list and an agreed dosing timetable for time-zone changes. Avoid driving or machinery when dizzy, unusually tired or unwell. Gentle activity can be adapted to energy levels; a child's limp needs assessment before continuing sport.

Tell surgeons and dentists that you take selpercatinib. US information requires a hold of at least seven days before elective surgery and no dosing for at least two weeks after major surgery and until adequate healing. The team must set the stop and restart dates; simply reaching two weeks does not establish that a wound is healed.

Ask about nutrition, intimacy, sleep and emotional support as needed. Keep fluid intake appropriate to your heart and kidney health. Report side effects that interfere with ordinary life early, because practical support or dose adjustment may make ongoing treatment more manageable.

Fertility contraception pregnancy and breastfeeding

Selpercatinib can harm an unborn baby. Pregnancy status is checked before treatment when relevant. Patients who can become pregnant need effective contraception throughout treatment and for one week after the last dose; European guidance specifies highly effective contraception for at least that interval. Male patients with a partner who could become pregnant also need effective contraception during treatment and for at least one week afterwards. Report a possible pregnancy promptly.

Do not breastfeed during treatment or for at least one week after the last dose. Other medicines may require longer precautions; the shortest interval does not override the rest of your treatment. Animal findings suggest possible effects on male and female fertility, but human effects are uncertain. Discuss fertility preservation before treatment when feasible, including age-appropriate counselling for younger patients.

After treatment finishes

Obtain a written follow-up plan, including blood tests, symptom review and the dates when reproductive precautions end. Continue to report persistent or new breathing problems, bleeding, rash or liver symptoms after stopping. A prior severe skin reaction must remain in your medical record.

Do not restart remaining tablets or capsules after a hospital admission, procedure or side-effect hold without instructions. Return unused supplies safely. If cancer control changes, the oncologist can explain what further assessment and treatment choices are appropriate.

Frequently asked questions