Ruxolitinib

MECHANISM OF ACTION

It works by blocking the JAK-STAT signaling pathway, which is involved in the regulation of blood cell production and immune function. By inhibiting this pathway, ruxolitinib reduces abnormal proliferation of blood cells, decreases inflammation, and alleviates disease-related symptoms such as splenomegaly and systemic manifestations in myeloproliferative disorders.

PHARMACOKINETICS

Absorption

Ruxolitinib is rapidly absorbed after oral administration, with a bioavailability of about 95% and peak plasma levels reached in roughly one hour. Food may slightly delay absorption but does not affect overall bioavailability. The drug is highly protein-bound (~97%) and its immediate-release tablets ensure quick and predictable absorption.

Distribution 

Ruxolitinib has a volume of distribution of about 72 L, indicating moderate distribution into body tissues. Its high protein binding (~97%) limits free drug in plasma but allows sufficient tissue penetration for therapeutic effect.

Metabolism

Ruxolitinib is primarily metabolized in the liver by the cytochrome P450 enzyme CYP3A4, with a minor contribution from CYP2C9. The metabolism produces inactive metabolites, which are mainly eliminated via the urine. Drug interactions with strong CYP3A4 inhibitors or inducers can significantly alter ruxolitinib exposure.

Elimination

Ruxolitinib is eliminated mainly through hepatic metabolism, with metabolites excreted in urine (about 74%) and feces (about 22%). Its elimination half-life is roughly 3 hours, supporting twice-daily dosing.

PHARMACODYNAMICS

Ruxolitinib selectively inhibits JAK1 and JAK2, blocking the JAK-STAT signaling pathway that regulates cytokine and growth factor activity. This reduces abnormal cell proliferation and inflammation, helping to improve symptoms, decrease splenomegaly, and modulate inflammatory cytokines in conditions like myelofibrosis and polycythemia vera.

ADMINISTRATION

Ruxolitinib is given orally as immediate-release tablets, usually twice daily. The dose is adjusted based on disease type, patient blood counts, and kidney or liver function. It can be taken with or without food, and tablets should not be crushed or split unless advised by a healthcare professional.

DOSAGE AND STRENGTH

Ruxolitinib tablets come in 5, 10, 15, and 20 mg strengths. Typical dosing is 5–20 mg twice daily for myelofibrosis and 10 mg twice daily for polycythemia vera, with adjustments for blood counts, kidney, or liver function.

DRUG INTERACTIONS

Ruxolitinib is metabolized by CYP3A4, so inhibitors (e.g., ketoconazole) can increase its levels, and inducers (e.g., rifampin) can reduce its effectiveness. Combining with other myelosuppressive drugs may increase the risk of low blood counts.

FOOD INTERACTIONS

Food may slightly delay the time to peak plasma levels but does not affect overall absorption or effectiveness.

CONTRAINDICATIONS

Ruxolitinib is contraindicated in patients with allergy to the drug or severe active infections. Caution is needed in severe liver or kidney impairment.

SIDE EFFECTS

• Anemia (low red blood cells) 

• Thrombocytopenia (low platelets) 

• Neutropenia (low white blood cells) 

• Dizziness and headache 

• Bruising or bleeding 

• Increased cholesterol levels 

• Weight gain 

• Infections (due to immune suppression) 

• Elevated liver enzymes

OVER DOSE

Overdose of ruxolitinib may lead to severe myelosuppression, including anemia, thrombocytopenia, and neutropenia, as well as increased risk of infections. Other symptoms can include dizziness, headache, and hypotension.

TOXICITY

Ruxolitinib toxicity mainly causes anemia, low platelets, and low white cells, increasing the risk of bleeding and infections. Liver enzyme elevation, headache, and dizziness may also occur.