Inrebic is an antineoplastic (used to treat cancer) prescription medicine and is also known by the generic name “Fedratinib.” Inrebic belongs to a class of medications known as JAK2 (Janus Associated Kinase 2) inhibitors and was first approved by the FDA in August 2019. In clinical settings, Inrebic is indicated for the treatment of intermediate-2 or high-risk primary or secondary myelofibrosis in adults, as well as related symptoms such as splenomegaly (spleen enlargement).
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Myelofibrosis is a chronic and rare form of blood cancer in which bone marrow (the soft and spongy tissues inside the large bones) becomes dense and fibrous by a process called fibrosis.
Since the bone marrow is responsible for producing various components of blood (e.g., red blood cells, white blood cells, and platelets), fibrosis interferes with the normal production of blood cells. As a result, immature blood cells are produced abnormally in excess. Because bone marrow can’t make adequate blood cells, the spleen partially takes over producing blood cells, and this results in a condition called splenomegaly (where the spleen gets bigger).
Inrebic comes in oral capsule form.
What Is Inrebic Used To Treat?
Inrebic is used as a targeted therapy to treat three types of myelofibrosis which include:
- Primary myelofibrosis (where the underlying cause is unknown).
- Post-polycythemia vera myelofibrosis (a disease linked to the overproduction of abnormal red blood cells by the bone marrow).
- Post-essential thrombocythemia myelofibrosis (a disease linked to the overproduction of platelets by the bone marrow).
As these diseases are less common, Inrebic is designated as an “orphan drug.”
How Does Inrebic Work?
In a healthy individual, the production of blood cells is tightly regulated by JAK2, which is a kinase enzyme that promotes the production, division, and growth of cells, among which are blood cells in the bone marrow.
In the case of patients with myelofibrosis, the JAK2 enzyme becomes overactivated and causes abnormal production of immature blood cells, and as a result, the spleen becomes significantly enlarged.
Inrebic works by inhibiting the JAK2 enzyme to slow down the abnormal growth of blood cells and relieve symptoms associated with myelofibrosis. Inrebic reduces spleen size, bone or muscle pain, itching, night sweats, pain under left-side ribs, and gastrointestinal discomfort.
Mode of Action
Inrebic contains an active substance, fedratinib, which acts as a kinase inhibitor and blocks the activity of the JAK2 enzyme.
Dosage Form and Strength
Inrebic is only available in 100 mg hard capsule form. This medication can only be obtained through a doctor’s prescription.
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Inrebic Dosing Information
The recommended dose of Inrebic for adults is 400 mg (four 100 mg capsules) once a day in patients with a baseline platelet count of more than or equal to 50,000/mm3.
However, the Inrebic dose might need to be reduced if patients have renal impairment or are taking other medications, such as strong CYP3A4 inhibitors. These dose adjustments must be done by the treating doctor.
What To Do if You Miss a Dose
Avoid taking a double dose of Inrebic to compensate for a missed dose. If you have forgotten your dose, skip the missed dose and take the next scheduled dose as prescribed by your doctor.
How Is Inrebic Used?
Inrebic capsules are taken orally, and they can be taken with or without food. However, if you experience stomach discomfort or get nausea or vomiting from the medication, taking Inrebic with a high-fat meal may help to lessen the chances of these side effects.
Your doctor may recommend other medications along with Inrebic to prevent vomiting, diarrhea, or nausea.
Inrebic capsules should be swallowed as is without chewing or crushing.
Possible Side Effects of Inrebic
Common Side Effects
Common Side Effects- Vomiting and nausea
- Diarrhea
- Anemia
- Low blood count (red and white blood cells), which temporarily decreases when you start Inrebic therapy. This decrease may put you at risk of infection, anemia, or bleeding.
- Low blood platelet level
- Low blood sodium
- Increase in liver enzymes (ALT and AST)
- Muscle spasms
- Weakness
- Increase in serum creatinine
- Indigestion
- Headache
- Loss of appetite
These are very common side effects that are temporary and quite manageable. For instance, vomiting and nausea can be relieved by taking OTC medications. Always consult with your doctor before taking any new medications.
Less Common Side Effects
Some less common side effects that are reported in patients receiving Inrebic include:
- Fatigue
- Bone pain
- Increased amylase enzyme
- Pain in the arms and legs
- Urinary tract infection
- Pain in extremities
- Weight gain
Rare But Severe Side Effects
The rare but potentially severe adverse reactions (reported in less than 1% of patients receiving Inrebic) include:
- Encephalopathy, including Wernicke’s encephalopathy, which is a neurologic condition caused by low levels of vitamin B1 (thiamine). Patients experience vision problems, confusion, memory impairment, and muscle movement and coordination difficulty.
- Thrombosis (deep venous thrombosis, pulmonary embolism, and arterial thrombosis), which occurs in patients receiving other JAK inhibitors for treating rheumatoid arthritis.
To avoid such complications, monitoring the vitamin B1 level in the patient’s body (before or during the Inrebic treatment) is highly recommended.
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Precaution & Recommendation
The following are some recommendations that patients should follow before or during Inrebic treatment:
- Do not take Inrebic if you are pregnant or planning to become pregnant. Inrebic can harm the unborn baby since this drug is absorbed through the skin and lungs.
- Do not take Inrebic if you are breastfeeding or planning to breastfeed. Since it is unknown whether this drug secretes into breast milk or not, it is recommended to avoid breastfeeding while taking Inrebic.
- Avoid Inrebic if you are allergic to fedratinib (an active component of Inrebic) or any other non-active element in this medication.
Be sure to tell your healthcare provider if you:
- Have renal impairment or rheumatoid arthritis.
- Have liver disease.
- Have thiamine (vitamin B1) deficiency.
- Are taking supplements, vitamins, or other JAK inhibitors.
US Boxed Warning: Encephalopathy, Including Wernicke
Serious and fatal encephalopathy, including Wernicke, has occurred in patients treated with fedratinib. Wernicke encephalopathy is a neurologic emergency. Assess thiamine levels in all patients prior to starting fedratinib, periodically during treatment, and as clinically indicated. Do not start fedratinib in patients with thiamine deficiency; replete thiamine prior to treatment initiation. If encephalopathy is suspected, immediately discontinue fedratinib and initiate parenteral thiamine. Monitor until symptoms resolve or improve and thiamine levels normalize.
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REFERENCES
- US Food and Drug Administration. Inrebic prescribing information https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/212327s004lbl.pdf
- European Medical Agency. Inrebic prescribing information https://www.ema.europa.eu/en/documents/product-information/inrebic-epar-product-information_en.pdf
- Bristol Myers Squibb Access Support. (n.d.). INREBIC® (fedratinib) | For Healthcare Professionals. https://www.inrebicpro.com/
- JAK2 gene: MedlinePlus Genetics. (n.d.). https://medlineplus.gov/genetics/gene/jak2
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Rafik Boctor, RPh was born and raised in Cairo, Egypt. He received his degree from the Faculty of Pharmacy, Helwan University in 2011. The most rewarding part of his job is making positive changes in patients’ health and well-being on a daily basis. His areas of expertise include immunoglobulins, chemotherapy and biologics. In his free time, he enjoys playing guitar, singing, and Latin dancing.