Idelalisib (Zydelig)

Idelalisib at a glance

Idelalisib, also called Zydelig, is a targeted medicine taken as tablets, usually twice a day. It blocks a signal that helps certain abnormal blood cells survive. A haematologist, a doctor specialising in blood disorders, decides whether it is appropriate for your treatment plan. It may be prescribed with another medicine such as rituximab.

Taking treatment at home does not mean that monitoring is optional. Idelalisib can cause serious infection and inflammation affecting the bowel, liver, lungs or skin. Blood tests and preventive medicines are an essential part of treatment, even when you feel well.

This guide explains practical care and warning signs. Your prescription and the instructions for your complete regimen take priority. Never change the dose, stop preventive treatment or restart a paused course without advice.

How idelalisib works

B lymphocytes are white blood cells that normally help defend against infection. In some blood cancers, abnormal B cells receive signals that help them multiply, survive and remain within supportive tissues. Idelalisib blocks an enzyme called PI3K-delta involved in these signals. This can reduce the survival and growth of abnormal cells.

PI3K-delta also has functions in normal immune cells. This helps explain why treatment can interfere with protection against infection and sometimes trigger unwanted inflammation. The word targeted describes its action; it does not mean the medicine affects only cancer cells.

Early in treatment, lymphocyte numbers in the blood may temporarily rise as cells move out of tissues. This rise alone does not necessarily mean that treatment has failed. Your team interprets it alongside symptoms, examination and other results rather than changing treatment because of one number.

How the team decides whether it is suitable

The decision includes your exact diagnosis, previous treatments, blood results, other illnesses, existing infections and personal priorities. Genetic tests may inform the wider treatment decision, but idelalisib is not simply selected by finding a PI3K mutation in a tumour. Do not assume that information about another PI3K inhibitor applies to this medicine.

Tell the team about liver disease, hepatitis, persistent diarrhoea, inflammatory bowel problems, lung disease, repeated infections and previous serious medicine reactions. Treatment should not start while a significant active infection remains untreated. European prescribing information specifically advises against starting during an ongoing systemic bacterial, fungal or viral infection.

A previous severe allergy to idelalisib must be disclosed. The US label also prohibits treatment in someone who has had toxic epidermal necrolysis, a severe skin reaction, from any medicine. The orange 100 mg tablet contains the colouring sunset yellow, which can cause allergic reactions.

Children are not covered by an established safe and effective dosing recommendation. Liver impairment needs individual assessment and closer observation; evidence in severe impairment is limited. Kidney problems do not automatically require a reduced starting dose, but dehydration and illness can still affect kidney function.

Before treatment starts

Expect blood tests for blood counts and liver function. Kidney function and other blood chemistry may also be checked. Tell the team about current or previous infections, including cytomegalovirus, usually shortened to CMV. People with evidence of previous CMV infection need a specific monitoring plan. Additional viral screening depends on your history and any partner medicine.

Everyone receiving idelalisib should have preventive treatment against Pneumocystis jirovecii pneumonia, or PJP. This is an infection that can become serious when immunity is weakened. Ask which preventive medicine you need, when to take it and whom to call if it causes a reaction. It may be an antibiotic such as co-trimoxazole, or an alternative chosen by the team.

Bring all prescribed and non-prescribed medicines, vitamins, herbal remedies and supplements to the pharmacy review. Mention pregnancy plans, breastfeeding and any difficulty swallowing tablets. A pregnancy test is recommended when relevant. Before the first dose, obtain your treatment calendar, blood-test dates and a 24-hour contact number.

How to take idelalisib

The daily routine

The usual adult dose is 150 mg twice daily, taken at approximately the same times each morning and evening. Tablets are available in 100 mg and 150 mg strengths. A lower dose, often 100 mg twice daily, may be prescribed after a treatment-related problem. These are reference doses, not instructions to adjust your own treatment.

Take the tablets with or without food and swallow them whole with water. Do not chew or crush them. No routine home method for making a liquid or administering through a feeding tube is provided in the sources used here; ask the pharmacist if swallowing is difficult.

Treatment does not normally have a weekly tablet-free break, but the intended duration depends on benefit, tolerability and the whole regimen. Another treatment given by infusion will have its own calendar. Keep the tablet and infusion instructions together so a change to one medicine is not mistaken for a change to both.

Missed tablets, vomiting and overdose

If less than six hours have passed since your usual dose time, take the missed dose and then continue your usual schedule. If more than six hours have passed, skip it. Never double the dose. The European professional information says within six hours, whereas US information and the European patient leaflet use less than six hours. At exactly that boundary, follow your pack instructions or ask your pharmacist rather than guessing.

If you vomit after a dose, do not take an extra tablet; take your next scheduled dose at the usual time unless the team advises otherwise. Contact the team for advice, particularly if vomiting continues or you cannot keep fluids down. If you take too much, contact the hospital urgently and bring the medicine pack.

Keep tablets in their labelled packaging, safely away from children, moisture and heat, following the storage instructions supplied. Do not share them. Ask the pharmacy how to return unused tablets safely.

Monitoring during treatment

Blood counts are checked at least every two weeks during the first six months under US and European guidance. If neutrophils, the infection-fighting white blood cells, fall substantially, checks may become weekly and treatment may be paused. A low count can be present before you notice symptoms.

Liver monitoring is especially important early on. US guidance specifies liver enzymes every two weeks for three months, every four weeks for the following three months, then every one to three months. European guidance specifies liver enzymes and bilirubin every two weeks for three months and thereafter as clinically needed. Abnormal results require more frequent checks, sometimes weekly. Your team chooses the schedule that fits your product and condition.

CMV monitoring is arranged when there is a previous infection or positive baseline testing. Blood tests can detect virus before obvious symptoms develop. US guidance calls for a treatment hold when viral testing becomes positive, until virus in the blood resolves; if treatment resumes, testing is at least monthly. European instructions distinguish symptom-free virus detection from detection accompanied by illness. These decisions belong to the treating specialist.

At appointments, report bowel frequency, cough, breathlessness, fever, rash and difficulty taking preventive medicines. Response is assessed through your symptoms, examination, blood tests and scans where appropriate. A treatment pause is a safety measure and does not, by itself, mean that the medicine has stopped working.

Common side effects and practical care

People experience different combinations of side effects. Studies often included other medicines, so a list or percentage from a combination study cannot predict what idelalisib alone will cause for you.

Loose stools and nausea

Report new diarrhoea promptly, even if you have taken idelalisib for months without trouble. Record how often you go, whether there is blood or mucus and whether you have pain or fever. Sip fluids; an oral rehydration solution may help if your team recommends it. Fluid restrictions for another illness still apply. Do not rely on repeated over-the-counter diarrhoea treatment to delay assessment.

For nausea, small meals and prescribed anti-sickness treatment may help. Repeated vomiting, reduced urine, dizziness or inability to drink need prompt advice because dehydration can develop.

Tiredness, appetite and skin discomfort

Balance rest with gentle activity that feels manageable. Tell the team if tiredness suddenly worsens or comes with breathlessness, fever or faintness; these can have a treatable cause. Small regular meals and dietitian support may help when appetite is poor.

For a mild itchy rash, use gentle washing products and ask about a suitable moisturiser or treatment. Report a new rash rather than assuming it is harmless. Painful skin, blisters, peeling, mouth sores or fever with a rash require urgent assessment.

Blood tests may reveal low white cells or raised liver enzymes without symptoms. Idelalisib can also raise triglycerides, a type of fat in the blood; the team may include lipid tests in monitoring. This is why feeling well should not be used as a reason to miss blood tests.

Important side effects to recognise

Infection and weakened immunity

Serious infections can occur, including pneumonia and bloodstream infection. They may happen with or without a very low white-cell count. Report fever, shaking chills, a new cough, painful urination or feeling suddenly unwell. Take PJP prevention consistently; it reduces risk but does not rule out infection.

Suspected PJP requires interruption and urgent investigation. Confirmed PJP requires permanent discontinuation under US instructions. CMV may reactivate, which means a previously controlled virus becomes active again. Symptoms are not specific enough to diagnose this yourself.

European information also describes reports of progressive multifocal leukoencephalopathy, or PML, a rare serious brain infection, in people with previous or concurrent immunosuppressive treatment. New changes in thinking, speech, vision, strength or coordination need urgent assessment; do not dismiss them as ordinary tiredness. If PML is suspected, treatment must be suspended while tests are arranged and must not resume unless PML has been excluded.

Bowel inflammation and perforation

Idelalisib can cause colitis, inflammation of the bowel. It can begin after several months and may worsen quickly. Standard medicines that slow diarrhoea may not control it. The team may test for infection, pause idelalisib and prescribe treatment such as a corticosteroid when appropriate. Do not start steroids yourself.

A hole in the bowel, called perforation, is another serious risk. Severe or worsening abdominal pain, especially with fever, chills or vomiting, requires emergency assessment. Do not wait until the number of loose stools reaches a particular threshold.

Liver and lung problems

Liver injury may first appear on blood tests. Yellow eyes or skin, dark urine, unusual upper abdominal pain, loss of appetite or marked tiredness need prompt advice. A pause, dose reduction or permanent stop may be necessary; US guidance requires stopping for recurrent liver toxicity.

New or worsening cough, breathlessness or low oxygen can reflect infection or treatment-related lung inflammation, called pneumonitis. The team must distinguish these urgently. Idelalisib is held while the cause is investigated. US instructions require permanent discontinuation for symptomatic pneumonitis or organising pneumonia; European guidance allows different decisions in selected milder cases, but requires permanent stopping for moderate or severe symptomatic disease or organising pneumonia. Never restart after a lung problem without specialist approval.

Severe skin reaction or allergy

Serious skin reactions include Stevens–Johnson syndrome, toxic epidermal necrolysis and DRESS, a reaction that can also affect internal organs. Painful widespread rash, blistering, peeling, mouth or eye sores, fever or facial swelling need urgent care. Suspected Stevens–Johnson syndrome, toxic epidermal necrolysis or DRESS requires interruption; a confirmed diagnosis requires permanent stopping. Other severe rashes also need an urgent specialist decision about treatment.

Sudden swelling of the lips, tongue or throat, wheezing, collapse or difficulty breathing may indicate a severe allergy. Seek emergency help and do not take further tablets while awaiting assessment.

Other medicines and vaccinations

Idelalisib interacts with many medicines because it and its breakdown products affect drug-processing enzymes. Simply separating tablets by a few hours will not reliably prevent these interactions. Ask the oncology pharmacist to check every new medicine, including short antibiotic courses, supplements and medicines given for a procedure.

Important examples include rifampicin and certain anti-seizure medicines, which can reduce idelalisib exposure; strong enzyme-inhibiting antibiotics or antifungals may increase it. St John's wort should be avoided. Idelalisib can raise concentrations of some sleeping tablets, opioids, heart medicines, psychiatric medicines and cholesterol medicines, including simvastatin. These examples are not a complete list. Do not stop an essential medicine on your own; the team may substitute, adjust or monitor it.

Warfarin may need closer clotting-test monitoring, including after idelalisib stops. Inhaled, nasal and oral steroids also need checking. Tell an anaesthetist about idelalisib before sedation or surgery. Inform your dentist before treatment too, so infection risk, blood counts and any prescribed medicines can be considered.

Vaccination should be planned with your team. Avoid live vaccines unless a specialist has confirmed they are appropriate; this can remain relevant after treatment ends. Non-live vaccines may be offered, although protection can be reduced. Timing depends on immune recovery and partner medicines such as rituximab, rather than a single universal waiting period.

Everyday life during treatment

A simple routine can make twice-daily treatment easier: use reminders, keep a dose record and arrange refills early. Ask before transferring tablets into another container. If you need help, a caregiver can maintain the calendar while leaving dose decisions to the clinical team.

Wash hands regularly, avoid close contact with people who are clearly unwell and follow food-safety advice. These precautions complement preventive medicines; they do not replace them. If someone at home receives a live oral or nasal vaccine, ask whether temporary precautions are needed.

Work, travel and exercise depend on how you feel and access to monitoring. Plan travel around blood tests and carry your medicines and emergency contact information. Avoid driving when weak, dizzy or unwell. Discuss alcohol with the team, particularly if liver tests are abnormal. Ask for support with sleep, anxiety, finances or the practical burden of repeated appointments.

Fertility, pregnancy and breastfeeding

Idelalisib may harm a developing baby. If you can become pregnant, use effective contraception during treatment and for one month after the last dose under US guidance. European guidance specifies highly effective contraception for that period and adding a barrier method if you use hormonal contraception, because its effectiveness with idelalisib is uncertain.

US instructions advise men with partners who can become pregnant to use effective contraception during treatment and for three months afterwards. European information does not provide the same fixed male interval. Ask for a written plan that covers both partners and every medicine in your regimen. A partner treatment can require substantially longer precautions.

Do not breastfeed during treatment. US instructions specify continuing this restriction for one month afterwards; European information does not give a fixed post-treatment interval. Do not restart breastfeeding without checking the whole treatment plan.

Human fertility effects are not established, but animal findings raise concern. Discuss sperm, egg or embryo preservation before treatment if relevant. If pregnancy occurs or is suspected, contact the team promptly for individual advice; do not assume a particular outcome.

After a pause or the end of treatment

Continue follow-up and report new symptoms even after tablets stop. Some inflammatory and infection-related problems need ongoing treatment or monitoring. A pause is not permission to restart when you feel better; the team may need blood results, imaging or evidence that an infection has resolved.

PJP prevention must not be stopped simply because idelalisib has ended. European guidance recommends continuing it for two to six months afterwards, with duration chosen according to factors such as steroid treatment and persistent low neutrophils. US prescribing information requires prevention during treatment without specifying that same post-treatment interval. Follow your specialist's written stop date.

Keep contraception and breastfeeding precautions in place for the required period, including any longer period for partner medicines. Before discharge from regular treatment visits, confirm who will arrange blood tests, infection follow-up and assessment of your blood disorder.

Frequently asked questions