About This Calculator

The Andexanet Alfa Dose Calculator helps healthcare professionals determine the appropriate dosing regimen for Andexxa® (andexanet alfa) when urgent reversal of anticoagulation from apixaban or rivaroxaban is required due to life-threatening or uncontrolled bleeding.

Outputs

Based on the inputs provided, the calculator determines one of two possible dosing regimens. The results include:

• Recommended Regimen: Either "Low Dose" or "High Dose".
• IV Bolus Details: The total dose in mg and the target administration rate (mg/min).
• IV Infusion Details: The total dose in mg to be administered over 120 minutes and the corresponding infusion rate (mg/min).
• Vial Requirement: The total number of 200 mg vials needed to prepare both the bolus and the infusion.

How to Use

To use the calculator, provide the following clinical information:

1. Factor Xa Inhibitor: Select whether the patient is taking apixaban or rivaroxaban.
2. Last Known Dose: Enter the patient's last dose in milligrams (mg). If this information is not available, check the "Dose is Unknown" box.
3. Time Since Last Dose: Enter the time in hours since the patient's last dose was administered. If the timing is uncertain, check the "Timing is Unknown" box.

After entering the data, click "Calculate Dose" to see the recommended regimen. Select "Other" for agents like edoxaban, though dosing is not established and requires clinical judgment.

Dosing Overview

Andexanet alfa dosing is based on the specific Factor Xa inhibitor, its dose, and the time since the last administration. The goal is to match the andexanet alfa dose to the amount of Factor Xa inhibitor likely present in the patient's circulation.

Low-Dose Regimen

The low-dose regimen (400 mg IV bolus followed by a 480 mg IV infusion) is recommended for patients with lower expected inhibitor levels. This applies if the patient was taking:

• Apixaban: Last dose of ≤ 5 mg taken ≥ 8 hours ago.
• Rivaroxaban: Last dose of ≤ 10 mg taken ≥ 8 hours ago.

High-Dose Regimen

The high-dose regimen (800 mg IV bolus followed by a 960 mg IV infusion) is used for all other scenarios, including:

• Higher doses of apixaban (> 5 mg) or rivaroxaban (> 10 mg).
• Doses taken more recently (< 8 hours ago).
• Cases where the dose or timing of the last administration is unknown.

Switching

Andexanet alfa is an acute, one-time treatment for the reversal of anticoagulation during a major bleed. It is not part of a scheduled therapy that involves switching. The decision to restart any anticoagulant therapy after the bleeding event is resolved must be based on the patient's clinical status, thrombotic risk, and bleeding risk.

Missed Dose

This section is not applicable. Andexanet alfa is administered as a single course (bolus followed by infusion) in an emergency setting for a specific indication. It is not a medication that is taken on a recurring schedule.

Safety Alerts

FAQ

Why is the high dose recommended if the dose or timing is unknown?

When the dose or time since last administration is unknown, it is impossible to confirm the patient meets the criteria for the low-dose regimen. To ensure adequate reversal in a potentially life-threatening situation, the high-dose regimen is recommended as a conservative approach.

What is the recommended dose for reversing edoxaban?

The dosing for reversing edoxaban has not been established in the official prescribing information. However, clinical studies like ANNEXA-4 have explored its use. The calculator notes that the high-dose regimen was used in these studies, but this constitutes an off-label use and requires careful clinical consideration.

How many vials are needed for each regimen?

The low-dose regimen requires 44 vials (20 for the bolus, 24 for the infusion). The high-dose regimen requires 88 vials (40 for the bolus, 48 for the infusion). Each vial contains 200 mg of andexanet alfa.

What is the final concentration after reconstitution?

Each 200 mg vial should be reconstituted with 20 mL of Sterile Water for Injection (SWFI), resulting in a final concentration of 10 mg/mL.

What is the administration rate for the IV bolus?

For both the low-dose and high-dose regimens, the initial IV bolus is administered at a target rate of 30 mg/min.

Can this calculator be used for reversing enoxaparin (Lovenox®)?

No, this calculator is specifically designed for apixaban and rivaroxaban per the FDA-approved indication. While andexanet alfa has been studied for enoxaparin reversal, dosing is not established, and it is considered an off-label use.

What is the correct dose if the last apixaban dose was 10 mg taken 12 hours ago?

The high-dose regimen would be recommended. Even though the dose was taken more than 8 hours ago, the dose amount (10 mg) is greater than the 5 mg threshold for the low-dose regimen.

Is there a dose adjustment for body weight?

No, the approved dosing for andexanet alfa is not adjusted for patient body weight.