Drug-induced myocarditis is inflammation of the heart muscle caused by a medicine or a reaction to it. It can affect how the heart pumps or how it beats. Medicines linked to this problem include some cancer immunotherapies, clozapine, certain antibiotics, and some diuretics. Warning signs may include chest pain, shortness of breath, a racing or uneven heartbeat, unusual tiredness, swelling, or fainting. Sudden or serious symptoms need emergency medical care.
What is drug-induced myocarditis?
Myocarditis occurs when the heart muscle, known as the myocardium, becomes inflamed. This inflammation can interfere with the heart's ability to pump blood effectively or maintain a normal rhythm. Drug-induced myocarditis refers to inflammation linked to a medicine rather than an infection or another underlying cause.
The reaction may involve an unusual immune response to a drug or another form of medicine-related injury. The heart may be affected alone or as part of a broader reaction involving other organs. The effects range from inflammation detected during medical monitoring to problems that affect heart function or cause dangerous changes in heart rhythm.
According to the Merck Manual, medications are among the recognized noninfectious causes of myocarditis. However, myocarditis can also result from infections, inflammatory diseases, and other exposures. Identifying the likely cause helps clinicians decide which investigations and treatments are appropriate.
Which medicines can cause myocarditis?
Drug-induced myocarditis is an uncommon complication, and the likelihood differs between medicines. A medication being associated with myocarditis does not mean that everyone who takes it will develop heart inflammation. The following groups are recognized potential causes.
- Immune checkpoint inhibitors: These cancer immunotherapy medicines help the immune system recognize and attack cancer cells. Examples include pembrolizumab, nivolumab, ipilimumab, and atezolizumab.
- Clozapine: This medicine is used to treat certain serious mental health conditions and has been associated with myocarditis.
- Some antibiotics: Certain antibiotics, including penicillins, have been linked to medication-related myocarditis.
- Some diuretics: These medicines help the body remove excess salt and water and are also listed among drugs associated with myocarditis.
- Certain chemotherapy medicines: Some medicines used in cancer treatment can be associated with inflammation of the heart muscle.
The MedlinePlus Medical Encyclopedia identifies reactions to certain medicines, including some chemotherapy drugs, as a possible cause of myocarditis. These examples are not a complete list, and the risk should be considered for the specific medicine rather than assumed to apply equally to an entire drug category.
Why can cancer immunotherapy affect the heart?
Immune checkpoint inhibitors work by changing how the immune system responds to cancer. In some people, this increased immune activity can also affect healthy tissues. When inflammation develops in the heart muscle, it is known as immune checkpoint inhibitor-associated myocarditis.
The National Cancer Institute describes myocarditis as a rare immune-related side effect of checkpoint inhibitor treatment. This possibility is important because the complication can interfere with heart function and may require urgent assessment. New chest discomfort, breathing difficulty, or an irregular heartbeat during this treatment should be reported promptly to the treating team.
What are the warning signs of drug-induced myocarditis?
The symptoms can resemble those of other heart, lung, or general medical conditions. Some people notice changes in their usual energy or exercise tolerance, while others develop more obvious symptoms. In some cases, myocarditis causes few noticeable symptoms at first and is identified through medical tests.
The Cleveland Clinic describes several symptoms that can occur with myocarditis, including chest pain, shortness of breath, fatigue, and heart palpitations. Examples of possible warning signs include:
- Chest pain or discomfort: Pain, pressure, or an uncomfortable feeling in the chest may occur when the heart muscle or nearby tissues are inflamed.
- Shortness of breath: Breathing may become difficult during everyday activities or at rest, particularly when heart function is affected.
- A racing or irregular heartbeat: The heart may feel as though it is beating unusually fast, skipping beats, or fluttering.
- Unusual tiredness or weakness: A person may feel more exhausted than expected or notice a reduction in their usual ability to exercise.
- Dizziness or fainting: These symptoms can occur when an abnormal heart rhythm or another problem affects blood flow.
- Swelling in the legs, ankles, or feet: Fluid may collect in these areas when the heart is not pumping effectively.
- Fever or a skin rash: These symptoms may accompany a medicine-related hypersensitivity reaction, although they do not establish that the heart is inflamed.
These symptoms are examples of experiences that can occur with myocarditis, not a checklist for identifying the condition. Their meaning depends on the person's medical history, current medicines, examination, and the pattern in which symptoms develop.
When should you seek emergency medical care?
Seek emergency medical care for new or significant chest pain, severe or sudden shortness of breath, fainting, or a rapid or irregular heartbeat accompanied by dizziness, weakness, or difficulty breathing. Do not delay care while trying to determine whether a medicine is responsible. Myocarditis can affect heart rhythm and pumping function, and other urgent conditions can cause similar symptoms.
Prompt assessment is especially important if these symptoms develop while taking an immune checkpoint inhibitor or another medicine associated with myocarditis. Tell the emergency team which medicines you take and when treatment began or changed. If possible, bring your medication list or the medicine packaging, but do not delay seeking help to collect these details.
New or worsening symptoms that are not immediately severe also deserve timely medical assessment, particularly after a medication has been started. A rash, fever, or swollen lymph nodes occurring alongside other concerning symptoms may provide additional information about a possible drug reaction. Do not wait for every possible symptom to appear before seeking care.
When can symptoms appear after starting a medicine?
There is no single timeline that applies to every drug or every person. The timing depends partly on the medicine involved and the nature of the reaction. Symptoms may begin after treatment starts, but the relationship between a medicine and new symptoms is not always obvious at first.
A review available through the U.S. National Library of Medicine's PubMed Central reports that immune checkpoint inhibitor-associated myocarditis often develops during the first few months of treatment. This is a pattern described for that specific type of treatment, not a universal deadline for all medicine-related myocarditis.
New symptoms should therefore be considered in the context of the complete medication history, rather than ruled out because a medicine was started weeks or months earlier. People receiving cancer treatment should follow the monitoring plan provided by their oncology team and report new symptoms promptly.
How do doctors assess possible drug-induced myocarditis?
There is no single symptom or test that establishes every case. Healthcare professionals consider the type of medicine being taken, when it was started, recent dose or treatment changes, other illnesses, and the nature of the symptoms. They also consider alternative explanations, including infection and other heart conditions.
Depending on the circumstances, an assessment may include:
- Medical history and examination: The clinician reviews medicines, symptoms, recent illnesses, and signs that may suggest a problem with the heart or circulation.
- Blood tests: Tests for cardiac troponin, a substance released when heart muscle cells are injured, may help identify heart damage. Other blood tests may assess inflammation or look for evidence of a drug-related reaction.
- Electrocardiogram (ECG): This records the heart's electrical activity and can help identify abnormal rhythms or other changes.
- Echocardiogram: An ultrasound examination that shows how the heart moves and pumps blood.
- Cardiac magnetic resonance imaging (MRI): This can help identify inflammation or injury in the heart muscle.
- Heart muscle biopsy: In selected cases, a small tissue sample may be needed to help confirm the diagnosis or identify a particular type of myocarditis.
The MedlinePlus Medical Encyclopedia describes ECG testing, blood tests, echocardiography, cardiac MRI, and sometimes a heart muscle biopsy as parts of the evaluation for myocarditis. Not everyone needs every test; the investigation depends on the clinical findings and the suspected cause.
What happens if a medicine is suspected of causing myocarditis?
Management depends on how the heart is affected, the suspected drug reaction, and the reason the medicine was prescribed. The treating team may need to pause or discontinue the suspected medicine and arrange treatment for the inflammation. The decision should be made urgently by an appropriate healthcare professional, particularly when the medicine is part of cancer treatment or is needed to manage a serious health condition.
Treatment may also involve medicines to manage heart failure or abnormal heart rhythms. Certain immune-mediated forms may require corticosteroids or other treatments that reduce inflammation. Hospital monitoring may be necessary when heart function or rhythm is affected.
Do not try to manage suspected drug-induced myocarditis by independently stopping, restarting, or changing prescription medicines. Seek urgent medical advice about the next dose, and do not delay emergency care to contact the prescribing clinician if serious symptoms occur.
Recovery depends on factors such as the cause, the extent of heart muscle injury, and the person's overall health. Some people recover their heart function, while others may need ongoing follow-up for persistent heart muscle damage or rhythm problems. The healthcare team can advise when follow-up tests or changes to usual activities are appropriate.
What information should you share with your healthcare team?
When seeking assessment, provide a complete list of prescription medicines, nonprescription medicines, supplements, and recent treatments. Include when each medicine was started, any recent changes, when the symptoms began, and whether they are getting worse. Mention any recent fever, rash, or other unusual symptoms, even if they seem unrelated.
For people receiving immunotherapy or cancer treatment, it is helpful to contact the treating oncology team promptly about new symptoms. If emergency warning signs occur, emergency assessment takes priority over arranging a routine appointment. Clear information about medication exposure can help clinicians investigate whether a drug reaction may be involved.