Pacritinib is a novel kinase inhibitor used to treat bone marrow fibrosis with severe thrombocytopenia. Its clinical application should focus on adverse reactions such as bleeding risk, cardiac toxicity, and gastrointestinal reactions. The following provides a detailed explanation of the mechanism of action, indications, and medication precautions.

1. Mechanism of action and indications

(1) Mechanism of action: Selective inhibition of the JAK2/IRAK1 pathway improves symptoms of bone marrow fibrosis and splenomegaly.

(2) Indications: Adult patients with medium to high risk primary or secondary myelofibrosis accompanied by thrombocytopenia (<50 × 10 ⁹/L).

(3) Therapeutic characteristics: It can be used without relying on platelet count, significantly improving anemia and transfusion needs.

2 Medication precautions

(1) Bleeding risk: Patients with active bleeding should not use it. During treatment, platelet monitoring should be conducted weekly. If bleeding symptoms such as bruising occur, seek medical attention immediately.

(2) Cardiotoxicity: Baseline electrocardiogram examination of QT interval, avoiding the use of QT prolonging drugs, and maintaining blood potassium levels above 4mEq/L.

(3) Gastrointestinal reactions: Loperamide should be used for grade 1-2 diarrhea, and medication should be temporarily suspended for grade 3 diarrhea; Nausea can be controlled with ondansetron.

3 doses and administration plan

(1) Standard dose: 200mg orally twice daily, taken on an empty stomach (1 hour before or 2 hours after meals).

(2) Dose adjustment: Suspend administration of grade 3 adverse reactions and reduce dosage to 100mg/dose after recovery; Level 4 permanent discontinuation of medication.

(3) Special population: Moderate to severe liver function impairment requires a 50% reduction in dosage, and end-stage renal disease patients do not need to adjust the dosage.

4 Adverse Reaction Management

(1) Hematological toxicity: Regularly monitor whole blood cell count, consider transfusion support for severe anemia.

(2) Infection risk: Patients with neutropenia need to prevent infection and seek medical attention immediately if they experience fever.

(3) Abnormal liver function: ALT/AST should be monitored monthly, and treatment should be interrupted if the liver toxicity is grade 3 or above.

5 Drug Interactions

(1) Strong CYP3A4 inhibitors: Avoid combination or reduce dosage by 50%, such as clarithromycin, itraconazole, etc.

(2) Anticoagulants: increase the risk of bleeding, closely monitor INR, and adjust warfarin dosage if necessary.

(3) Proton pump inhibitors: may reduce the absorption of pakinib, it is recommended to take them every 2 hours.