Methoxyisobutylisonitrile
Methoxyisobutylisonitrile (MIBI), used clinically as technetium-99m sestamibi (brand name Cardiolite; generic kits are also available), is a radioactive diagnostic agent used in nuclear medicine imaging.
Pronunciation: (meh-THOK-see-eye-soh-BYOO-till-eye-soh-NYE-trile).
- Generic name
- Methoxyisobutylisonitrile
- Brand names
- Cardiolite, MIBI, Sestamibi
- Drug class
- General Medical Info
Availability and supply rules vary by country
Trade names by country:
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What Methoxyisobutylisonitrile is and how it works
Methoxyisobutylisonitrile (MIBI), used clinically as technetium-99m sestamibi (brand name Cardiolite; generic kits are also available), is a radioactive diagnostic agent used in nuclear medicine imaging. It is FDA-approved to help doctors visualize blood flow to the heart (myocardial perfusion imaging) and as a second-line imaging test after an abnormal mammogram to help evaluate breast lesions. This agent works by attaching to a radioactive tracer (technetium-99m), which is injected into your bloodstream. The tracer travels to specific organs or tissues, allowing special cameras to capture detailed images. These images help your healthcare provider assess heart function, detect blockages, or locate abnormal tissue. Key points for patients: According to the US label, about 27% of the injected dose leaves the body in the urine and about 33% in the feces over 48 hours. Your imaging team will tell you how to prepare for the test. Always inform your healthcare team about allergies, pregnancy, or breastfeeding. (1) (3)
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how Methoxyisobutylisonitrile works
Technetium Tc 99m sestamibi is a cationic Tc 99m complex that accumulates in viable myocardial tissue in a manner analogous to that of thallous chloride Tl-201. Studies suggest cellular retention occurs within the mitochondria, but the clinical relevance of this has not been determined (US label, section 12.1). (1)
What is Methoxyisobutylisonitrile used for?
Myocardial perfusion imaging — detecting coronary artery disease by localizing reversible (ischemia) and non-reversible (infarction) defects, and evaluating myocardial function.
Myocardial perfusion imaging — detecting coronary artery disease by localizing reversible (ischemia) and non-reversible (infarction) defects, and evaluating myocardial function. (1) (3)
Breast imaging — a second-line diagnostic test used AFTER an abnormal mammogram or a palpable breast mass, to help evaluate breast lesions. It is not a breast-cancer screening test, it cannot confirm or rule out cancer, and it is not an alternative to biopsy.
Breast imaging — a second-line diagnostic test used AFTER an abnormal mammogram or a palpable breast mass, to help evaluate breast lesions. It is not a breast-cancer screening test, it cannot confirm or rule out cancer, and it is not an alternative to biopsy. (1) (3)
Before taking Methoxyisobutylisonitrile
Do not take / not appropriate for
- The US label lists no contraindications ("None known"). Tell the imaging team if you have had an allergic reaction to sestamibi or another imaging agent before, because rare severe allergic reactions have been reported. (Contraindication) (1)
Tell your clinician about
(1) (3)Methoxyisobutylisonitrile dosage and how to take it
- General Instructions: Methoxyisobutylisonitrile is administered by a healthcare professional in a hospital or imaging center. You do not take this medication at home.. Adult Dosing: A single IV dose of 10-30 mCi (370-1110 MBq) is used for cardiac (myocardial perfusion) imaging, and 20-30 mCi (740-1110 MBq) for breast imaging, depending on the specific imaging protocol.. Pediatric Dosing: Safety and effectiveness have not been established in children, and the label gives no pediatric dose.. Administration: Given as an intravenous injection, followed by imaging at specific time intervals. You may be asked to exercise or receive a medication to simulate exercise during cardiac imaging.. When To Stop: The procedure is a single-use diagnostic test. No ongoing dosing is required.. Storage: Not applicable for patients. Storage is managed by healthcare professionals according to radiation safety protocols.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (3)
Missed dose
If you miss your scheduled imaging appointment, contact your healthcare provider promptly to reschedule. Do not attempt to self-administer this medication.
Overdose
The US label states that the clinical consequences of an overdose of technetium Tc 99m sestamibi are not known. The dose is prepared and given by trained staff. If you have concerns, contact the nuclear medicine team, your doctor, or emergency services. (1) (3)
Methoxyisobutylisonitrile side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Headache
Incidence: About 0.2-1.6% in clinical studies (US label)
Nausea
Incidence: About 0.1-0.6% in clinical studies (US label)
Flushing
Incidence: A few cases reported (US label)
Chest pain
Incidence: Chest pain/angina in about 2.1% of cardiac-study patients (US label)
Dizziness
Incidence: 0.5% or less (US label)
Rash
Incidence: A few cases reported (US label)
Hives, swelling, or difficulty breathing after the injection (possible hypersensitivity/anaphylactic reaction)
Incidence: Rare
Chest pain, palpitations, severe dizziness, or fainting during or after a stress-test portion of the scan
Incidence: Rare, but can reflect a serious cardiac event during stress testing
Serious warnings
When this scan is combined with pharmacologic or exercise cardiac stress testing, serious adverse events can occur, including heart attack, abnormal heart rhythm, low blood pressure, airway tightening, and stroke-type events — serious
Symptoms: When this scan is combined with pharmacologic or exercise cardiac stress testing, serious adverse events can occur, including heart attack, abnormal heart rhythm, low blood pressure, airway tightening, and stroke-type events; deaths have infrequently occurred 4 to 24 hours after administration, usually associated with exercise stress testing. The US label states that in patients with known or suspected heart disease, care should be taken to assure continuous monitoring and treatment in accordance with safe, accepted clinical procedure.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1) (3)
Rare but serious hypersensitivity/anaphylactic reactions (swelling, generalized hives) have occurred, including on a second injection within the same imaging visit — serious
Symptoms: Rare but serious hypersensitivity/anaphylactic reactions (swelling, generalized hives) have occurred, including on a second injection within the same imaging visit. Inform your doctor if you are pregnant, planning pregnancy, or breastfeeding, and report any history of allergic reactions to radioactive imaging agents.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1) (3)
There are no contraindications on the current US label ("None known") — serious
Symptoms: There are no contraindications on the current US label ("None known"). However, serious allergic reactions have occurred, so before the injection you should be asked about any previous allergic reaction to this agent, and emergency equipment should be available. The radiation dose to the ovaries from this agent is high compared with most other diagnostic technetium-labeled agents, which is relevant to pregnancy counseling.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1) (3)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Other medicines | The US label states that specific drug-drug interactions have not been studied. Tell the imaging team about all medicines and supplements you take. | (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
The current CARDIOLITE (US) label states that limited data in pregnant women have not identified a drug-associated risk of major birth defects, miscarriage, or other adverse outcomes, but that all radiopharmaceuticals have the potential to cause fetal harm depending on the stage of pregnancy and the radiation dose. If the scan is considered during pregnancy, you should be told about the possible risks. Tell the imaging team if you are or might be pregnant. (1) (3)
Breastfeeding
The current CARDIOLITE (US) label states that only about 0.01% to 0.03% of the injected activity passes into breast milk, so it is not necessary to interrupt breastfeeding. However, the label advises that a breastfeeding woman should consider restricting close contact with her baby to a maximum of 5 hours in the 24 hours after the injection, to reduce the infant's radiation exposure. (1) (3)
Children
Safety and effectiveness have not been established in pediatric patients. Clinical studies of children and adolescents with Kawasaki disease found no evidence of diagnostic efficacy for that use. (1) (3)
Monitoring
(1) (3)Storage
Not applicable for patients — this agent is prepared and administered entirely by healthcare professionals. For clinical reference: the unlabeled kit is stored at 15-25 degC (59-77 degF) before and after preparation, and the radiolabeled (reconstituted) product is used within 6 hours of preparation.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General (US label)
Indication: Myocardial perfusion imaging / breast imaging
Dose summary: Cardiac: 370-1110 MBq (10-30 mCi) single IV dose. Breast: 740-1110 MBq (20-30 mCi) single IV dose.
Renal context: No renal-impairment-specific dose adjustment is defined on the label reviewed in this pass. (1)
Frequently asked questions
What is methoxyisobutylisonitrile used for?
It is FDA-approved as a radiopharmaceutical agent for imaging the heart (myocardial perfusion scans) and, as a second-line test after an abnormal mammogram, for evaluating breast lesions.
Is methoxyisobutylisonitrile safe?
It is given only by trained staff in a nuclear medicine department. The US label warns that serious events, including heart attack, abnormal heart rhythm, low blood pressure, narrowing of the airways and stroke, can occur when the scan is combined with cardiac stress testing, and that rare severe allergic reactions have occurred. In clinical studies the most common reaction was a temporary change in taste (about 7% in cardiac studies). (1)
Can I have this scan if I am pregnant or breastfeeding?
Tell your doctor if you are pregnant or breastfeeding. The US label says the radiation risk to a fetus depends on the stage of pregnancy and the radiation dose, and you should be told about this before the scan. Breastfeeding does not need to be interrupted, but the label advises considering limiting close contact with your baby to a maximum of 5 hours in the 24 hours after the injection.
How long does the radioactive tracer stay in my body?
According to the US label, about 27% of the injected dose leaves the body in the urine and about 33% through the feces within 48 hours. The radioactive label (technetium-99m) also decays over time. (1)
Will I feel anything during the injection?
The injection is given into a vein. In US clinical studies the most common reaction was a temporary metallic or altered taste (about 7% in cardiac studies). Tell the staff straight away if you notice hives, swelling or trouble breathing.
Are there any long-term risks from the radiation?
The US label states that the radiation dose to the ovaries from this agent (1.5 rads per 30 mCi at rest) is high compared with most other diagnostic technetium-labeled agents, so exposure should be kept as low as reasonably achievable in women who could become pregnant. Ask the nuclear medicine team about the dose you will receive. (1)
What happens if I take too much Methoxyisobutylisonitrile (diagnostic agent)?
The US label states that the clinical consequences of an overdose of technetium Tc 99m sestamibi are not known. The dose is prepared and given by trained staff. If you have concerns after your scan, contact the nuclear medicine team or your doctor. (1)
Is Methoxyisobutylisonitrile (diagnostic agent) safe during pregnancy?
The US label states that the radiation risk to a fetus depends on the stage of pregnancy and the radiation dose, and that the radiation dose to the ovaries from this agent is high compared with most other diagnostic technetium-labeled agents, so exposure should be kept as low as reasonably achievable in women who could become pregnant. Tell your healthcare provider if you are or might be pregnant so the risks can be discussed before the test.
What is the mechanism of action of Methoxyisobutylisonitrile?
Technetium Tc 99m sestamibi is a cationic Tc 99m complex that accumulates in viable myocardial tissue in a manner analogous to that of thallous chloride Tl-201. Studies suggest cellular retention occurs within the mitochondria, but the clinical relevance of this has not been determined (US label, section 12.1). (1)
What is the generic name of Methoxyisobutylisonitrile?
The generic name is Methoxyisobutylisonitrile. It is sold under brand names including Cardiolite, MIBI, Sestamibi.
What class of drug is Methoxyisobutylisonitrile?
Methoxyisobutylisonitrile is classed as: General Medical Info.
References
- CARDIOLITE (Lantheus) Kit for the Preparation of Technetium Tc99m Sestamibi — prescribing informationU.S. Food and Drug Administration via DailyMed · United States · accessed 2026-10-13 · source 1
- Kit for the Preparation of Technetium Tc 99m Sestamibi Injection (Cardinal Health 414, LLC) — prescribing informationU.S. Food and Drug Administration via DailyMed · United States · accessed 2026-10-13 · source 2
- Drugs@FDA: ANDA078809 overviewU.S. Food and Drug Administration · United States · accessed 2026-10-13 · source 3
Brand names by country
Single-ingredient Methoxyisobutylisonitrile names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.