Ivosidenib (Tibsovo)

Ivosidenib at a glance

Ivosidenib, also called Tibsovo, blocks an abnormal form of the IDH1 enzyme. It comes as 250 mg film-coated tablets and is usually taken once daily. The prescribed number of tablets can change because of interactions or side effects.

Tiredness, nausea, diarrhoea, reduced appetite, abdominal discomfort and changes in blood tests can occur. Important risks include changes to the heart's electrical rhythm and, in particular blood-cancer settings, differentiation syndrome. The latter is an inflammatory reaction that needs immediate treatment.

This guide is about ivosidenib itself. Where another medicine such as azacitidine accompanies it, your team will provide a separate calendar and explain the additional precautions. Side effects observed with a combination should not all be attributed to one component.

What ivosidenib is and how it works

IDH1 stands for isocitrate dehydrogenase 1, an enzyme involved in cell chemistry. Certain changes, or mutations, make IDH1 produce excess amounts of a substance called 2-hydroxyglutarate. This can interfere with normal cell development and help a cancer survive.

Ivosidenib inhibits susceptible mutated IDH1. By reducing the abnormal chemical signal, it can slow cancer growth and, in some blood cancers, help immature cells develop into more mature cells. This process is called differentiation. This cell-changing process can also cause differentiation syndrome. Having this syndrome is not, by itself, a reliable measure of how well treatment is working.

Ivosidenib is not conventional chemotherapy or a checkpoint immunotherapy. It is not interchangeable with medicines that target IDH2 or with other IDH inhibitors. A similar-sounding target does not mean the same medicine is suitable. Targeted treatment can still affect healthy tissues and cause serious adverse effects.

How the team decides whether it is suitable

A laboratory must confirm a susceptible IDH1 mutation in the cancer. European instructions specify an IDH1 R132 mutation. The sample and test depend on the diagnosis: the team may use blood, bone marrow or tumour tissue. Finding a mutation helps select treatment, but does not guarantee benefit.

Your specialist considers the diagnosis, previous treatment, overall health, organ function and applicable prescribing information together. Ask what your result means and how it influences the proposed treatment. Safety and effectiveness in children have not been established in the reviewed product information.

Heart-rhythm history is particularly important. Tell the team about fainting, congenital long-QT syndrome, unexplained sudden deaths in close relatives, heart failure or previous abnormal ECGs. European information excludes certain serious rhythm conditions and a markedly prolonged QT interval. An alternative treatment may be safer for some people.

Severe kidney disease, dialysis, liver impairment, very low body weight or low albumin need careful assessment. Albumin is a blood protein that can reflect nutrition and other aspects of health. These circumstances may change monitoring or the benefit–risk discussion; do not adjust your own dose.

Before treatment starts

You will have blood counts and chemistry tests, including kidney and liver function and important blood salts called electrolytes. Potassium and magnesium are especially relevant to heart rhythm. The team will correct significant abnormalities and arrange an ECG, a painless recording of the heart's electrical activity.

Bring an up-to-date list of all prescribed and non-prescribed medicines, supplements and herbal products. Include occasional anti-sickness tablets, antibiotics, antifungals, pain medicines, heart medicines and contraception. An interaction check is essential even if you have taken a medicine safely for years.

Discuss any current infection, previous hepatitis or other important viral infection, swallowing problem, pregnancy possibility and breastfeeding. Viral screening or infection-prevention medicine may be appropriate for the complete treatment plan, especially with other cancer drugs. This is not a universal antiviral prescription for everyone taking ivosidenib.

Tibsovo contains lactose. European information says people with rare hereditary galactose intolerance, total lactase deficiency or glucose–galactose malabsorption should avoid it. These conditions are different from ordinary dietary lactose intolerance; tell your pharmacist about any diagnosed sugar-intolerance disorder.

Before leaving the clinic, know how to reach your treating hospital's urgent advice service. If differentiation syndrome is relevant to your treatment, obtain and carry the patient alert card where provided, and make sure a caregiver understands the warning symptoms.

How treatment is taken

Daily dose and calendar

The usual adult starting dose is 500 mg once daily, taken as two 250 mg tablets. A specialist may prescribe 250 mg daily because of an interaction or adverse effect. Take the current prescribed amount at approximately the same time each day; never alternate doses or increase tablets yourself.

When used with azacitidine, ivosidenib is generally taken throughout the 28-day cycle, including days when azacitidine is not given. Do not assume that an injection-free day is a tablet-free day. Your written calendar takes priority if the team has deliberately paused treatment.

Treatment often continues while it is helping and side effects remain manageable. In relevant blood-cancer settings, several months may be needed to assess response: US information recommends allowing at least six months if there is no progression or unacceptable toxicity. This does not mean unsafe treatment should continue to meet a time target.

Food and swallowing

Food instructions differ between regions. European and UK instructions require an empty stomach: no food for two hours before taking the tablets and one hour afterwards. US information permits taking them with or without food but specifically prohibits taking the dose with a high-fat meal.

Food can change how much medicine enters the bloodstream and increase the risk of rhythm problems. Follow the instructions issued for your supply; do not switch between meal routines because an overseas website gives different advice. Avoid grapefruit and grapefruit juice.

Swallow tablets whole with water. Do not split, crush, chew or dissolve them. If swallowing is difficult or you use a feeding tube, contact the specialist pharmacist before the next dose for an individual plan. The reviewed labels do not provide a routine home dispersion or tube-administration method.

Missed doses, vomiting and accidental extra tablets

If you forget a dose, take it when remembered only if the next scheduled dose is at least 12 hours away. Otherwise skip it and resume the normal schedule. Never take two doses less than 12 hours apart or double a dose to catch up. If the timing is uncertain, ask the pharmacist.

If you vomit after taking it, do not take replacement tablets. Take the next scheduled dose at the usual time. Repeated vomiting needs prompt advice because dehydration and lost electrolytes can also increase heart-rhythm risk. If you accidentally take extra tablets, seek urgent medical advice and take the medicine packaging with you.

Storage and handling

Keep tablets in their original, tightly closed bottle, away from children. Keep the moisture-absorbing canister in the bottle and never swallow it. US storage instructions specify 20–25°C (68–77°F), with permitted brief excursions to 15–30°C (59–86°F); European information requires no special temperature conditions but protection from moisture. Follow your pack and ask about safe storage in hot weather. Return unused tablets to the pharmacy for disposal.

Monitoring and checking whether treatment is working

ECGs are required before treatment and at least weekly for the first three weeks. They then continue monthly when results permit, with extra checks for symptoms, an abnormal result or an interacting medicine. A normal first ECG does not remove the need for later monitoring.

Blood tests check counts, kidney and liver function and electrolytes. European information recommends checks at least weekly in month one, every other week in month two, and at each subsequent medical visit. US information specifies this initial schedule for acute myeloid leukaemia (AML) or myelodysplastic syndromes (MDS), followed by monthly testing, and weekly creatine phosphokinase during the first month. This enzyme can rise with muscle injury. Your diagnosis and results determine the actual schedule.

The team assesses benefit using symptoms, examinations and the tests appropriate to your disease, such as scans or blood and bone-marrow assessments. There is no single scan interval or blood result that suits every patient. Report changes between visits rather than waiting for the next planned test.

Treatment may be interrupted, reduced or stopped for abnormal ECGs, severe toxicity or other safety concerns. After a rhythm change, repeat ECGs and correction of electrolytes or interacting medicines help guide restarting. A pause can be a planned safety measure; restart only when instructed.

Common side effects and practical management

Tiredness and anaemia

Fatigue can affect concentration and everyday tasks. Plan important activities for times when energy is better, take short rests and include gentle movement when safe. Anaemia means too few oxygen-carrying red blood cells and can contribute to tiredness, dizziness or breathlessness. Tell the team about new or worsening symptoms; blood tests may show a treatable cause.

Nausea, vomiting and reduced appetite

Eat small, manageable meals and sip fluids regularly, fitting meals around your prescribed tablet window. Take anti-sickness medicine exactly as supplied, because some alternatives can affect the QT interval. Ask for review if nausea prevents eating or drinking. A dietitian can help with ongoing weight loss or poor intake.

Diarrhoea and dehydration

Report diarrhoea early, particularly if it persists or occurs with cramps, dizziness or poor drinking. Use only the anti-diarrhoea plan approved by your team. Replace fluids within any heart or kidney restriction. Very little urine, inability to keep fluids down, blood in stools or marked weakness needs urgent assessment. Losing potassium or magnesium through diarrhoea adds to rhythm risk.

Abdominal discomfort and swelling

Abdominal pain and fluid accumulation in the abdomen, called ascites, may occur, particularly in the solid-tumour setting. Clothing may feel tighter and eating or breathing may become uncomfortable. Tell the team promptly rather than assuming this is ordinary weight gain. New severe pain, rapidly increasing swelling or breathlessness needs urgent assessment.

Mouth, skin, muscle and nerve symptoms

Some patients develop mouth soreness, rash, itching, or muscle and joint aches. Gentle mouth care, a soft toothbrush and an unperfumed moisturiser may help; ask before adding medicated products. Report symptoms that affect eating, walking or sleep. New tingling or numbness should also be assessed, particularly if it progresses or is accompanied by weakness.

Different treatment settings have different side-effect patterns. Blood-count suppression is especially relevant with blood cancers and accompanying azacitidine; swelling or abdominal symptoms may have several causes. The team should assess the cause rather than automatically blaming the tablet.

Less common but important side effects

Differentiation syndrome

This risk is particularly relevant to people treated for acute myeloid leukaemia, or AML, and is also included in US warnings for myelodysplastic syndromes, or MDS. It is not presented as the same expected risk for every solid-tumour patient. Rapid changes in developing blood cells can trigger inflammation, fluid build-up and organ dysfunction.

Warning signs include unexplained fever, breathlessness, cough, rapidly increasing weight, swollen limbs, dizziness or faintness, and reduced urine. Fluid can collect around the lungs or heart. Symptoms may appear very early; US studies reported onset from one day to three months after starting treatment. It can happen with or without a raised white blood cell count.

Contact the treating team immediately for suspected symptoms. Severe breathing difficulty or collapse needs emergency care. Tell the assessing clinician you take ivosidenib and may have differentiation syndrome. Infection and other serious problems can look similar; you should not try to decide the cause at home.

Hospital treatment includes prompt corticosteroids and close monitoring, with other measures as needed. High white-cell counts may need a separate medicine or procedure. Do not stop prescribed steroids early: the syndrome can recur. The specialist decides whether ivosidenib must be paused; simply missing a tablet is not a substitute for urgent treatment.

Heart-rhythm changes

Ivosidenib can prolong the QT interval, meaning the heart takes longer than usual to reset electrically between beats. This may cause a dangerous rhythm. It can be silent on symptoms, which is why ECGs matter, or cause palpitations, dizziness or fainting.

Report palpitations or new dizziness immediately. Fainting, collapse, chest pain or severe breathlessness requires emergency assessment. Avoid driving yourself. Treatment may need holding or reducing; QT prolongation accompanied by a life-threatening rhythm requires permanent discontinuation under the labels.

Infection, low platelets and biochemical changes

Low infection-fighting white cells increase infection risk; low platelets increase bruising and bleeding. Fever, shaking chills, unusual bruising, nosebleeds or blood in urine or stools needs prompt assessment. A serious infection is possible even without a high temperature. Your team may arrange transfusions, infection treatment or changes to the overall regimen.

Liver tests, bilirubin, kidney function or blood salts can become abnormal. Report yellow skin or eyes, dark urine, substantially reduced urine, severe muscle pain or weakness. In blood-cancer care, rapidly changing cell numbers can also contribute to tumour lysis syndrome, a potentially serious disturbance of blood chemistry. Monitoring and any preventive measures depend on individual risk.

Guillain–Barré syndrome

The US label warns about this serious nerve disorder. New or worsening weakness, tingling, difficulty walking, facial weakness or altered sensation needs urgent medical assessment. Weakness affecting breathing or swallowing is an emergency. If Guillain–Barré syndrome is diagnosed, the US label requires ivosidenib to be permanently stopped.

Other medicines, supplements and vaccinations

Ivosidenib is affected by enzymes that process medicines, especially CYP3A4, and can itself change the breakdown of other drugs. Interactions can make it less effective or increase toxicity, including QT prolongation. Have every new or stopped medicine checked by the oncology pharmacist.

Important examples include certain antibiotics and antifungals, epilepsy medicines, rifampicin, heart-rhythm medicines, some anti-sickness medicines and St John's wort. Strong enzyme-inducing medicines should be avoided. Strong or moderate inhibitors may require a substitute, extra ECGs or a specialist dose change; US and European dose-adjustment rules are not identical.

Antifungal selection needs particular care: ivosidenib can lower the effectiveness of some antifungals while an antifungal can also increase ivosidenib exposure. Do not stop infection prevention without arranging an alternative with the team.

European information prohibits combining it with dabigatran. Warfarin, some statins, fentanyl and diuretics also need individual checking. Tell the pharmacist about reflux treatment such as omeprazole; its effectiveness may change. Taking these medicines a few hours apart does not reliably prevent an interaction; your pharmacist should advise on alternatives or monitoring.

Discuss vaccines with the team. Live vaccines may be unsuitable during immune suppression; the timing depends on your full treatment and immune recovery. Non-live vaccines may be offered, although protection can be reduced. There is no single post-treatment vaccine interval that applies to everyone taking this medicine.

Everyday life during treatment

Use reminders or a written record to support your daily routine, and note symptoms and any missed dose. Continue varied meals and safe activity as tolerated. Ask for help with fatigue, sleep or anxiety rather than struggling alone. Caregivers can help notice changes in swelling, walking or alertness.

Do not drive or operate machinery if dizzy, faint, unusually tired or weak. Discuss work adjustments and travel before booking: early ECG and blood-test appointments are important, and access to urgent care must be practical. Keep medicines in original packaging and plan storage and time-zone changes with the pharmacist.

Tell dentists and surgeons about treatment and recent blood results. Procedures may require coordination because of infection risk, low platelets or interacting medicines; do not create your own treatment break. Hand hygiene, safe food handling and avoiding close contact with people who are unwell are sensible when immunity is reduced.

Fertility, contraception, pregnancy and breastfeeding

Ivosidenib may harm a developing baby. If you could become pregnant, European guidance recommends a pregnancy test before treatment. Contact the team immediately if you or your partner becomes pregnant. European information advises effective contraception for patients who could become pregnant and male patients with partners who could become pregnant, during treatment and for at least one month afterwards.

Hormonal methods such as pills, patches or implants may become less reliable. A suitable additional barrier method or alternative contraception is needed; ask for a specific plan. US information also warns about reduced hormonal contraceptive effectiveness but does not specify the same fixed post-treatment contraception interval. Do not interpret that absence as permission to conceive immediately.

Do not breastfeed during treatment or for at least one month after the final dose. The effect on human fertility is unknown; animal findings suggest possible reproductive effects. Discuss sperm or egg preservation before starting if future parenthood matters to you. Accompanying medicines may require longer precautions, which the shorter ivosidenib interval must not override. For example, European azacitidine information requires contraception during treatment and for at least six months afterwards for women, and at least three months afterwards for men. Obtain a written plan covering every medicine.

After treatment finishes

Ask for a written plan covering the last dose, follow-up tests, symptom monitoring and continuing medicines. Some adverse effects take time to settle. Continue seeking urgent help for concerning symptoms rather than assuming the risk ended with the final tablet.

Interactions may persist beyond stopping, and the team must review medicines that were previously changed. Continue contraception and breastfeeding precautions for the agreed duration. Return unused tablets; never restart from an old supply without a new instruction. Follow-up focuses on both the cancer and recovery from treatment.

Frequently asked questions