What are the differences in premonitoring investigations for initiation of therapy with baricitinib (Janus kinase inhibitor) and ritlecitinib (Janus kinase inhibitor)?

Differences in Premonitoring Investigations for Baricitinib and Ritlecitinib Therapy

For both baricitinib and ritlecitinib, baseline screening includes complete blood count with differential, liver function tests, renal function tests, TB screening, hepatitis B and C testing, and lipid profile, but ritlecitinib additionally requires thyroid function monitoring if used with levothyroxine. 1, 2

Common Baseline Investigations for Both JAK Inhibitors

Infectious Disease Screening

• Tuberculosis (TB) screening
• Hepatitis B virus (HBV) testing (anti-HBs, anti-HBc, HBsAg)
• Hepatitis C virus (HCV) testing
• HIV testing if risk factors are present 1, 2

Laboratory Testing

• Complete blood count (CBC) with differential
• Liver function tests (particularly transaminases)
• Renal function tests
• Lipid profile 1, 2

Clinical Assessment

• History and risk assessment for venous thromboembolism (VTE)
• Cardiovascular risk assessment
• Baseline skin examination for patients at risk of non-melanoma skin cancer
• Chest X-ray (unless recently performed) 1

Vaccination Status

• Assessment of vaccination status
• Consideration of pneumococcal, influenza, and recombinant zoster vaccines
• Completion of live vaccines before initiating therapy 1, 2

Key Differences in Premonitoring Investigations

Specific to Ritlecitinib

1. Thyroid Function Testing:

   • Ritlecitinib requires thyroid function monitoring if used concurrently with levothyroxine 2
   • Not specifically required for baricitinib

2. Platelet Count Requirements:

   • Ritlecitinib is not recommended in patients with platelet count <150 × 10^9 cells/L 2
   • Baricitinib does not have this specific platelet count threshold requirement

Specific to Baricitinib

1. Age-Related Considerations:
   • Baricitinib requires dose reduction to 2 mg daily for patients over 70 years of age due to age-related reductions in renal function 1
   • No specific age-related dose adjustments are mentioned for ritlecitinib

Monitoring Recommendations After Initiation

For Baricitinib

• CBC with differential and comprehensive metabolic panel at 4-8 weeks after starting, and every 3 months thereafter
• Lipid profile at 4-8 weeks after starting, then annually 1

For Ritlecitinib

• CBC with differential, liver enzymes at 4 weeks after initiation
• Lipid profile at 4 weeks after initiation
• Regular monitoring every 3-6 months thereafter 2

Important Considerations for Both Medications

Renal Function

• Both medications have restrictions for severe renal impairment (eGFR <30 mL/min)
• Baricitinib specifically requires dose adjustment for mild-to-moderate renal impairment 1, 2

Hepatic Function

• Neither medication should be used in patients with severe hepatic disease (Child-Pugh C)
• No dosage adjustment needed for mild or moderate (Child-Pugh A/B) hepatic impairment 1, 2

Safety Monitoring

• Both require monitoring for signs of infection, with temporary discontinuation during serious infections
• Treatment interruption is recommended for both medications if laboratory abnormalities occur:
  • Hemoglobin <8 g/dL
  • Absolute lymphocyte count <0.5 × 10^9 cells/L
  • Absolute neutrophil count <1 × 10^9 cells/L
  • Platelet count <50 × 10^9 cells/L 1, 2

Understanding these differences in premonitoring investigations is crucial for safe initiation of therapy with either baricitinib or ritlecitinib, as proper baseline screening helps identify patients at increased risk for adverse events and allows for appropriate monitoring during treatment.