Ruxolitinib

Mechanism of Action

Ruxolitinib falls under the drug class known as janus kinase inhibitors (JAK Inhibitors). It is an inhibitor of the JAK1 and JAK2 protein kinases and works by competitively inhibiting the ATP-binding catalytic site on JAK1 and JAK2.[4] The result of this inhibition is disruption of cytokine and growth factor signaling pathways, leading to a decrease in proinflammatory cytokines and chemokines, which are usually elevated in myelofibrosis and other inflammatory conditions. Furthermore, JAK1 is involved in regulating interleukin 2 and 6 and TNF alpha, while JAK2 is involved with many cellular functions that include proliferation and differentiation.

Due to its anti-JAK activity, ruxolitinib has been reported to improve splenomegaly seen in myelofibrosis and other constitutional symptoms such as fevers, pruritus, and night sweats. However, ruxolitinib is not known to alter the actual bone marrow or cause prolonged survival in myelofibrosis.[4] Moreover, in mice models, ruxolitinib has been shown to reduce inflammation as well as decrease T-cell activation and neutrophil activity.[11]

The drug has a half-life of 3 hours for the parent drug and approximately 6 hours for its active metabolites. It is hepatically metabolized via the CYP450 enzymatic pathway, specifically CYP2C9 and CYP3A4. It is mostly excreted in the urine (75%) and to a lesser extent in the feces (approximately 20%.)[12]

Administration

Ruxolitinib is taken orally and is available in 5 mg, 10 mg, 15 mg, 20 mg, and 25 mg tablets. The dosing regimen is based on the patient’s individual situation as well as blood results. For example, when treating myelofibrosis, the dose is dependent on the patient’s baseline platelet counts. Patients with myelofibrosis who have a platelet count between 50 to 100 x 10^9/L can take up to a maximum of 5 mg twice daily, while patients with a platelet count of above 100 x 10^9/L can take a maximum of 15 mg twice daily.

In contrast, patients with polycythemia vera should be started on 10 mg twice daily as a starting dose. In non-responders dose can be increased to 25 mg twice daily if hemoglobin, neutrophil counts, and platelets are normal. It is important to keep in mind that ruxolitinib should not be taken with grapefruit or grapefruit juice due to possible interaction causing increased exposure to ruxolitinib; however, patients can take it with other food or without depending on patient preference.[13]

Dosing for acute graft-versus-host disease is 5 to 10 mg orally twice daily, starting a 5 mg twice daily for 3 days, then increasing to 10 mg twice daily. For chronic graft-versus-host disease, the recommended dosing is 10 mg twice daily. Dose adjustments may be necessary for patients who have failed prior treatment based on their bilirubin, ANC, or platelet responses.[14]

Clinicians need to consult advanced prescribing information in cases of renal or hepatic impairment. In dialysis patients, dosing should be after dialysis on dialysis days.[15]

Ruxolitinib may also be used in pediatric patients with graft-versus-host disease; dosing is similar to adult dosing, and the clinician should consult package inserts for the most precise dosing and adjustments based on hepatic or renal status in pediatric patients.[15]

Adverse Effects

During the COMFORT trials, the most common nonhematologic adverse events included ecchymosis, headache, dizziness, abdominal pain, fatigue, and diarrhea. The most common hematological adverse events seen with ruxolitinib during the trials included anemia and thrombocytopenia due to the inhibition of JAK2, which plays a role in erythropoietin and thrombopoietin signaling.[13] Other potentially serious hematologic adverse events include anemia and neutropenia. 

It has been reported that patients taking ruxolitinib experience higher rates of herpes zoster infection and basal-cell and squamous-cell carcinomas.[16] One study analyzing ruxolitinib in patients with steroid-refractory acute graft-versus-host disease mentioned patients developing anemia, thrombocytopenia, and cytomegalovirus infection while on ruxolitinib.[17]

Contraindications

There are few specific contraindications when it comes to prescribing ruxolitinib; however, there are medications and foods that should be used with caution alongside ruxolitinib. For example, as previously mentioned, grapefruit and grapefruit juice should not be taken alongside ruxolitinib due to possible interaction. Further, when taking potent CYP3A4 inhibitors such as clarithromycin, nelfinavir, and voriconazole alongside ruxolitinib, the ruxolitinib dose should be reduced as all these medications cause increased exposure to ruxolitinib. Careful consideration is necessary when fluconazole is taken alongside ruxolitinib as it inhibits both CYP3A4 and CYP2C9 and causes increased exposure to ruxolitinib. Hence, the dose of fluconazole should not exceed 200 mg daily when taken alongside ruxolitinib.[13]    

Other drug contraindications include concomitant ruxolitinib use with live vaccines.

Ruxolitinib is contraindicated in patients whose creatinine clearance is below 15 and who are not on hemodialysis. Patients should not breastfeed during treatment and for two weeks following discontinuation of treatment.[18]

Clinicians need to exercise caution when prescribing ruxolitinib to patients who smoke or are past smokers, those with a creatinine clearance below 60, patients with hepatic impairment, and those with infection risks, particularly TB-related risk.

Monitoring

Patients starting or continuing ruxolitinib need to be monitored in multiple domains. Due to the increased risk of infection, all patients require monitoring for signs of infection throughout treatment while taking ruxolitinib. Studies have shown increased rates of urinary tract infections, hepatitis, pneumonia, tuberculosis, and herpes zoster infection; therefore, clinicians should keep this in mind, and patients should be screened for signs of infection.[19] Clinicians should perform tuberculosis screening in high-risk patients to investigate for any active or latent tuberculosis infection prior to starting ruxolitinib treatment.

It is also recommended to check the patient's complete blood count in individuals with myelofibrosis before starting ruxolitinib and continue to check this every two to four weeks until the dose of ruxolitinib has stabilized. Once drug levels have stabilized, a complete blood count only needs to be done every eight to twelve weeks or when clinical suspicion warrants it.[13]

Toxicity

Toxicities that may accompany therapy with ruxolitinib include hematological toxicities, which encompass cytopenia and anemia. In one study looking at the efficacy of ruxolitinib in patients with corticosteroid-refractory graft-versus-host disease when cytopenia occurred, it required a dose reduction, interruption in treatment, or permanent cessation of ruxolitinib.[19] Furthermore, when patients’ platelet count drops below 50 x 10^9/L with an original baseline greater than 100 x 10^9/L, ruxolitinib needs to be stopped to avoid further toxicity. The same can be said for patients with a baseline platelet count of 50 x 10^9/L that drops below 25 x 10^9/L. Ruxolitinib can be restarted once counts normalize.

Also, during the COMFORT trials, hemoglobin levels in patients decreased in the first eight to twelve weeks; however, levels improved after twelve weeks. Moreover, patients with renal impairment should reduce their ruxolitinib dose, as should patients with hepatic impairment.[13] Lastly, one study examining the relationship between ruxolitinib and cardiac repolarization found no evidence of ruxolitinib affecting the QT interval.[20]

Enhancing Healthcare Team Outcomes

Ruxolitinib is a medication that is currently being used to treat several different medical conditions and was the first medication for treating patients with steroid-refractory acute graft-versus-host disease. Hence, all healthcare professionals should be aware of its indications and monitoring requirements.

Due to the adverse effects and hematological toxicities associated with ruxolitinib, patients need to be monitored closely by all interprofessional healthcare team members, including clinicians (MDs and DOs), mid-level practitioners (NPs and PAs), nurses, and pharmacists. Due to hematological toxicities, it is crucial to monitor complete blood count in these patients until ruxolitinib doses stabilize. All team members should also ask patients about possible signs of infection due to increased infection rates with ruxolitinib so that ruxolitinib can be stopped if necessary. Nurses should also be able to answer questions about medication administration and serve as a contact point for when patients or other team members need to contact the prescribing clinician. Pharmacists will perform medication reconciliation and reinforce patient counseling points, including proper dosing and watching for potential adverse events. If they encounter any interactions or notice adverse events, they must immediately report these to the nursing staff so the clinician can adjust therapy as necessary.

By working together, the interprofessional healthcare team can allow for optimal treatment and monitoring that will enable patients to carry through with their long-term treatment with ruxolitinib. [Level 5]