The Apixaban Dosage Calculator determines the appropriate apixaban dosage based on specific patient information. This involves considering the patient's age, weight, creatinine clearance, and the reason for using apixaban. Here’s how the process works:

- **Inputs**:
  - Age is captured in years, with a range of 18 to 120.
  - Weight can be entered either in kilograms (30 to 300 kg) or pounds (66 to 660 lb). If in pounds, it's converted to kilograms using a conversion rate (1 kg = 2.20462 lb).
  - Creatinine clearance is measured in mL/min, ranging from 0 to 150.
  - The indication for use includes four options: Atrial Fibrillation (AF), Deep Vein Thrombosis (DVT), Pulmonary Embolism (PE), or Postoperative Thromboprophylaxis.

- **Computation**:
  - For **Atrial Fibrillation (AF)**:
    - The dosage is tailored based on three criteria:
      - Age of 80 years or older.
      - Weight of 60 kg or less.
      - Creatinine clearance of 30 mL/min or less.
    - If a patient meets two or more of these criteria, the dosage is reduced to 2.5 mg twice daily. A note explains the reason for dosage reduction.
    - If fewer than two criteria are met, the standard dosage is 5 mg twice daily.

  - For **Deep Vein Thrombosis (DVT)** and **Pulmonary Embolism (PE)**:
    - An initial higher dose of 10 mg twice daily for the first 7 days is recommended, followed by 5 mg twice daily. This regimen is aimed at acute treatment. A note provides context on the dosing strategy.

  - For **Postoperative Thromboprophylaxis**:
    - The suggested dose is 2.5 mg twice daily, with a note indicating its purpose in preventing thrombosis after surgery.

- **Output**:
  - The calculator returns the determined apixaban dosage accompanied by relevant notes if applicable. These notes provide critical context for clinical decision-making, clarifying the reasoning behind dosage adjustments based on patient characteristics and treatment indications. 

The structured assessment assures the apixaban dosage is well-suited to the patient's needs, adhering to clinical guidelines and ensuring safety and efficacy aligning with their health condition.

The Apixaban Dosage Calculator is a clinical tool to determine the appropriate dosage of apixaban, a direct oral anticoagulant (DOAC) used for thromboprophylaxis and treatment of thromboembolic conditions such as atrial fibrillation (AF), deep vein thrombosis (DVT), and pulmonary embolism (PE). The dosage depends on three factors: age, weight, and renal function (creatinine clearance). The recommended dose in atrial fibrillation is 2.5 mg twice daily in patients with at least two of the following three characteristics: age >= 80 years, body weight <= 60 kg, and serum creatinine >= 1.5 mg/dL.