About This Calculator

The Omnitrope® (somatropin) Dose Calculator is a clinical tool designed for healthcare professionals to aid in determining the appropriate dosing regimen for patients. It performs calculations based on patient weight, height, the specific indication for use, and the selected formulation. This tool helps streamline the process of dose administration planning for both pediatric and adult patients according to approved guidelines.

Calculator Outputs

After entering the required patient and dosing information, the calculator provides the following key outputs:

• Total Weekly Dose: The total amount of somatropin in milligrams (mg) to be administered over one week.
• Total Daily Dose: The calculated dose in milligrams (mg) for each injection day, based on the total weekly dose and administration frequency.
• Required Injection Volume: The volume in milliliters (mL) required for each injection to deliver the calculated daily dose, specific to the chosen formulation's concentration.
• Supply Estimation: An estimate of the number of cartridges or vials needed per month and the approximate number of days each unit will last, aiding in prescription and supply management.

How to Use the Calculator

Follow these steps to calculate a patient's dose:

1. Select Unit System: Choose between Metric (kg, cm) or Imperial (lbs, in) units.
2. Enter Patient Data: Input the patient's current weight and height. The tool will automatically calculate the Body Surface Area (BSA) using the Mosteller formula.
3. Choose Indication: Select the appropriate FDA-approved indication from the dropdown menu (e.g., Pediatric GHD, Turner Syndrome, Adult Onset GHD).
4. Specify Dosing Approach: For adult indications, select either the recommended non-weight-based or the alternative weight-based starting dose approach.
5. Input Prescribed Dose: Enter the prescribed dose based on the selected approach (either mg/kg/week or mg/day). Guideline ranges are provided for reference.
6. Set Injection Frequency: Select the number of injection days per week (e.g., 6 or 7 days/week).
7. Select Formulation: Choose the specific Omnitrope® formulation being prescribed (SurePal™ Cartridge or Vial). If using the vial, confirm the diluent volume.
8. Calculate: Click the "Calculate Dose" button to view the results.

Dosing Overview

Omnitrope® dosing is highly individualized and depends on the patient's condition, weight, and response to treatment. For pediatric indications like Growth Hormone Deficiency (GHD), dosing is typically weight-based, often in the range of 0.16 to 0.24 mg/kg/week. For conditions like Prader-Willi Syndrome (PWS) or Idiopathic Short Stature (ISS), different weight-based guidelines apply. For adults, treatment may be initiated with a lower, non-weight-based dose (e.g., 0.15-0.3 mg/day) and titrated based on clinical response and IGF-I concentrations to minimize side effects. All dosing decisions must be based on clinical judgment and the full prescribing information.

Switching Between Somatropin Products

Omnitrope® is a biosimilar to Genotropin®. When switching a patient from another recombinant human growth hormone product, a milligram-for-milligram (1:1) dose conversion is generally appropriate. However, it is crucial to monitor the patient's clinical response and serum IGF-I levels after the switch to ensure therapeutic efficacy and safety, adjusting the dose as necessary.

Handling a Missed Dose

If a patient misses a dose of Omnitrope®, they should be instructed to take it as soon as they remember. However, if it is almost time for the next scheduled dose, they should skip the missed dose and resume their regular administration schedule. Patients must be advised not to take a double dose to make up for the one they missed. Consistent administration is key to achieving the best therapeutic outcomes.

Safety Alerts

Healthcare professionals should be aware of key safety considerations when prescribing Omnitrope®. It is contraindicated in patients with acute critical illness, active malignancy, or known hypersensitivity. Important safety points based on indication include:

• General: Injection sites should be rotated regularly to prevent lipoatrophy.
• Prader-Willi Syndrome: Monitor for signs of upper airway obstruction or sleep apnea. Discontinue treatment if these occur.
• Turner Syndrome: Monitor patients for glucose intolerance and otitis media.
• Adults: Use caution and lower starting doses in elderly patients or those with risk factors for fluid retention or glucose intolerance.

This is not a complete list of risks. Always consult the most current Full Prescribing Information before making any clinical decisions.

Frequently Asked Questions (FAQ)

How does the calculator determine Body Surface Area (BSA)?
The calculator uses the Mosteller formula, a widely accepted method, which calculates BSA (m²) as the square root of [(Height(cm) × Weight(kg)) / 3600].

What is the difference between weight-based and non-weight-based dosing for adults?
Non-weight-based dosing is the recommended starting approach for adults, beginning with a low fixed dose (e.g., 0.2 mg/day) that is gradually increased. Weight-based dosing calculates the daily dose based on the patient's body weight, which may be an option for some patients but can increase the risk of side effects.

Why is the default injection frequency 6 days a week?
A 6-day-per-week schedule is common in clinical practice to provide a "rest day," which can improve patient adherence and reduce injection site fatigue. However, the dosing schedule should be determined by the prescribing physician.

Can I use this calculator for other brands of somatropin?
No. This calculator is specifically designed for the concentrations and formulations of Omnitrope® (SurePal™ cartridges and 5.8 mg vial). Using it for other products could lead to incorrect injection volumes and dosing errors.

What happens if I use a different diluent volume for the vial?
The tool defaults to the standard 1.14 mL diluent volume. If you use a different volume to reconstitute the 5.8 mg vial, you must enter that exact volume into the "Diluent Volume" field to ensure the final injection volume is calculated correctly based on the new concentration.

Does the calculator account for dose titration over time?
No, the tool calculates the administration volume for a single, specific dose prescribed at one point in time. It does not provide a titration schedule. Dosage adjustments should be made by the clinician based on ongoing patient monitoring.

Is the monthly supply estimate an exact figure?
The supply estimate is an approximation based on 4.333 weeks per month. It is intended for guidance in prescription planning, but actual usage may vary slightly.

Why is Omnitrope® prescribed for Small for Gestational Age (SGA)?
It is prescribed for children born SGA who fail to demonstrate catch-up growth by age 2 to 4 years. Treatment helps improve growth velocity and final adult height.

References

1. Omnitrope (somatropin) injection, for subcutaneous use. Full Prescribing Information. Sandoz Inc. Silver Spring, MD: U.S. Food and Drug Administration.
2. Omnitrope® for Healthcare Professionals. Sandoz Inc.
3. Omnitrope (somatropin) European public assessment report (EPAR). European Medicines Agency.
4. Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987 Oct 22;317(17):1098.