About This Tool

The Xeljanz (tofacitinib) Dose Calculator is a clinical support tool designed to assist healthcare professionals in determining the appropriate dosage regimen for patients. It processes key inputs such as the specific indication, patient weight (for pediatric use), renal and hepatic function, and potential drug-drug interactions to provide dosing recommendations aligned with prescribing guidelines.

Outputs

After calculating, the tool provides a clear output summary that includes:

• Recommended Dose: The specific milligram strength and frequency (e.g., 5 mg twice daily).
• Formulation: Specifies the appropriate formulation (e.g., Immediate-Release, Extended-Release, or Oral Solution).
• Dosing Adjustments: If a dose modification is required, the tool will state the adjusted dose and list the reasons, such as "Renal Impairment" or "Drug Interaction."
• Important Notes: Provides critical context, such as recommendations to switch formulations if an adjustment is needed for an extended-release product.

How to Use

Follow these steps to determine the correct tofacitinib dose:

1. Select Indication: Choose the patient's condition (e.g., Rheumatoid Arthritis, Ulcerative Colitis).
2. Choose Formulation: Select the intended drug formulation (IR, XR, or Oral Solution). Note that available options change based on the indication.
3. Enter Patient Factors: Input patient weight for pediatric (pcJIA) indications. Select the appropriate levels of renal (CrCl) and hepatic (Child-Pugh) function.
4. Indicate Drug Interactions: Check the box if the patient is taking a potent CYP3A4 inhibitor or a combination of a moderate CYP3A4 and potent CYP2C19 inhibitor.
5. Calculate: Click the "Calculate Dose" button to view the recommendation.

Dosing Overview

Standard dosing for tofacitinib varies significantly by indication and patient factors. Key examples include:

• Rheumatoid Arthritis, Psoriatic Arthritis, Ankylosing Spondylitis: The typical dose is 5 mg IR twice daily or 11 mg XR once daily. This is reduced to 5 mg IR once daily in patients with certain risk factors.
• Ulcerative Colitis (Induction): 10 mg IR twice daily for at least 8 weeks. This is reduced to 5 mg IR twice daily for patients requiring adjustment.
• Ulcerative Colitis (Maintenance): 5 mg IR twice daily or 11 mg XR once daily. This is reduced to 5 mg IR once daily for patients requiring adjustment.
• Polyarticular JIA (pcJIA): Dosing is weight-based, administered as an oral solution or 5 mg IR tablet, typically twice daily. The dose is reduced to once daily if adjustments are needed.

Switching Formulations

Dose adjustments are often not possible with the extended-release (XR) formulation. If a patient on Xeljanz XR 11 mg requires a dose reduction due to renal impairment, hepatic impairment, or a drug-drug interaction, they should be switched to Xeljanz 5 mg (Immediate-Release) once daily. The calculator automatically provides this recommendation.

Missed Dose

If a patient misses a dose of Xeljanz or Xeljanz XR, they should take it as soon as they remember. If it is nearly time for their next scheduled dose, they should skip the missed dose and resume their regular dosing schedule. The patient should not take two doses at the same time to make up for a missed one.

Safety Alerts

This information is not a substitute for clinical judgment. Always consult the full prescribing information for complete details on warnings and precautions.

Frequently Asked Questions

Why is the weight field only visible for pcJIA?
Dosing for polyarticular juvenile idiopathic arthritis (pcJIA) is weight-based, while dosing for adult indications is standardized. The tool requires weight only when it is a factor in the calculation.

What happens if I select "Severe Hepatic Impairment"?
The calculator will display an error message stating that Xeljanz is contraindicated, as its use is not recommended in patients with Child-Pugh C liver impairment.

Why is Xeljanz XR unavailable for UC Induction?
The approved induction dose for Ulcerative Colitis is 10 mg twice daily, which can only be achieved with the immediate-release (IR) formulation. Xeljanz XR is only indicated for UC maintenance therapy.

Does the calculator account for interactions with medications like fluconazole?
Yes. Fluconazole is a moderate CYP3A4 inhibitor and a potent CYP2C19 inhibitor. This interaction is covered by selecting the "Moderate CYP3A4 + Potent CYP2C19 inhibitor" checkbox, which will trigger a dose adjustment.

What CrCl value is considered "moderate" renal impairment?
The calculator defines moderate renal impairment as a Creatinine Clearance (CrCl) between 30 and less than 60 mL/min, as per the prescribing information.

Can I use the 5 mg tablet for a 45 kg child with pcJIA?
Yes. For patients with pcJIA weighing 40 kg or more, the recommended dose is 5 mg, which can be administered as the immediate-release tablet instead of the oral solution.

Why does the calculator recommend switching from XR to IR for dose adjustments?
The 11 mg extended-release tablet cannot be split or crushed, and a lower-strength XR version is not available. Therefore, the only way to achieve the required reduced dose (e.g., 5 mg once daily) is by switching to the immediate-release formulation.

What is the lowest weight for which the pcJIA calculation is valid?
The tool calculates doses for patients with pcJIA weighing 10 kg or more. It will show an error for weights below this threshold.

References

• XELJANZ (tofacitinib) Prescribing Information. U.S. Food and Drug Administration.
• Xeljanz Dosing and Administration. Pfizer HCP Portal.
• Xeljanz (tofacitinib) Summary of Product Characteristics (SmPC). European Medicines Agency.
• American College of Rheumatology (ACR) Guideline for the Treatment of Rheumatoid Arthritis.