About This Dosing Tool

This Norditropin Pen Dose Calculator is a reference tool for qualified healthcare professionals to assist in dose planning and administration for patients prescribed Norditropin® (somatropin). It helps translate a prescribed dose rate into a specific number of clicks for various Norditropin® prefilled pens (FlexPro® and NordiFlex®) and estimates pen duration based on the calculated regimen.

All calculations should be independently verified. This tool is not a substitute for clinical judgment or the official prescribing information.

Understanding the Calculator Outputs

After entering the required patient and prescription data, the calculator provides the following key outputs:

• Total Weekly Dose: The total amount of somatropin (in mg) the patient should receive over a full week, based on their weight and the prescribed dose rate.
• Ideal Dose per Injection: The mathematically precise dose (in mg) for a single injection, calculated by dividing the total weekly dose by the number of injections per week.
• Actual Delivered Dose: The dose (in mg) that will be delivered by the pen, based on rounding the ideal dose to the nearest full click. Pen devices can only deliver medication in discrete increments.
• Clicks per Injection: The number of clicks to dial on the selected pen to deliver the actual dose. This is the primary actionable output for patient instruction.
• Variance and Pen Duration: The calculator highlights the percentage difference between the ideal and actual dose. It also provides an estimate of how long one pen will last with the specified dosing schedule.

How to Use the Calculator

To ensure accurate results, follow these steps and input the correct information into each field:

1. Patient Weight: Enter the patient’s current weight. You can toggle the unit between kilograms (kg) and pounds (lbs). The tool will automatically convert lbs to kg for calculations.
2. Prescribed Dose Rate: Input the prescribed dose rate (e.g., 0.024). Select the correct unit from the dropdown: either mg/kg/week or mg/kg/day.
3. Injections per Week: Select the number of injections the patient will administer per week (typically 6 or 7).
4. Select Pen Type: Choose the specific Norditropin® pen that has been prescribed from the list (e.g., FlexPro® 5 mg, 10 mg, 15 mg, or NordiFlex® 30 mg).

General Dosing Overview

Norditropin® dosing is highly individualized based on the patient’s specific indication (e.g., Pediatric Growth Hormone Deficiency, Turner Syndrome, Adult Growth Hormone Deficiency), weight, and clinical response. Dosing should always be initiated and supervised by a physician experienced in the diagnosis and management of patients with growth hormone disorders.

• Pediatric Dosing: Typically calculated based on weight (mg/kg) and administered daily. Common weekly doses range from 0.17 to 0.37 mg/kg per week, divided into 6-7 subcutaneous injections.
• Adult Dosing: May be initiated with a low, non-weight-based dose (e.g., 0.2 mg/day) and titrated upwards based on clinical response and serum IGF-1 concentrations.

Switching Between Pen Strengths

When switching a patient from one Norditropin® pen strength to another (e.g., from a FlexPro® 5 mg to a 10 mg pen), it is critical to recalculate the dose in clicks. The dose increment (mg per click) is different for each pen type. Use this calculator to re-verify the number of clicks required to deliver the same intended dose in milligrams.

Managing a Missed Dose

If a dose of Norditropin® is missed, the patient should take the next scheduled dose as planned. They should not double the dose to make up for the missed one. The regular administration schedule should be resumed. If multiple doses are missed, the patient should contact their healthcare provider for guidance.

Important Safety Alerts

Norditropin® is contraindicated in patients with acute critical illness, active malignancy, diabetic retinopathy, and in children with closed epiphyses. Key warnings and precautions include:

• Increased risk of mortality in patients with acute critical illness.
• Risk of second neoplasms in childhood cancer survivors.
• Potential for intracranial hypertension.
• Can cause or worsen glucose intolerance and diabetes mellitus.

Frequently Asked Questions

Why is the “Actual Delivered Dose” different from the “Ideal Dose”?

Prefilled pens like FlexPro® deliver medication in fixed increments per click. The calculator rounds the ideal dose to the nearest possible click, resulting in an “actual” dose that is deliverable by the device. This is why a slight variance often exists.

What should I do if the calculated variance is high (>5-10%)?

A high variance suggests the pen’s increment may not be ideal for the prescribed dose. Consider discussing with the prescriber whether a different pen strength (with a smaller click increment) or a slight adjustment to the total weekly dose would be clinically appropriate.

Can I use this calculator for other growth hormone products like Genotropin or Humatrope?

No. This calculator is specifically designed for the drug concentrations and click increments of Norditropin® FlexPro® and NordiFlex® pens. Using it for other products will result in dangerous dosing errors.

How does the calculator handle the lbs vs. kg weight conversion?

When “lbs” is selected, the tool converts the input weight to kilograms using the standard conversion factor (1 kg ≈ 2.20462 lbs) before calculating the dose.

What if the calculated dose is less than one click?

The calculator will show an error. A dose less than the smallest increment of the pen cannot be administered. This situation requires clinical re-evaluation, such as selecting a different pen strength with a smaller increment or reassessing the prescribed dose rate.

How is the pen duration estimated?

It is calculated by dividing the total milligrams in the pen by the average daily dose (Total Weekly Dose / 7). This is an estimate and does not account for the small amount of drug used for priming the needle.

Does this tool account for the drug used during priming?

No, the pen duration estimate is based solely on the therapeutic doses administered. Patients should be advised that the actual duration may be slightly shorter due to the small volume used for the pre-injection air shot/priming.

Is this tool a substitute for the official prescribing information?

Absolutely not. It is an educational aid. The official Prescribing Information provided by Novo Nordisk is the sole source of definitive guidance for the use of Norditropin®.

References

1. Norditropin® (somatropin) injection, for subcutaneous use. Full Prescribing Information. Novo Nordisk Inc., Plainsboro, NJ. Available at: https://www.novo-pi.com/norditropin.pdf
2. Novo Nordisk. Norditropin® for Healthcare Professionals. Official Manufacturer Website. Available at: https://www.norditropinpro.com/
3. U.S. Food and Drug Administration. Drugs@FDA: Norditropin. FDA Application No. 021148. Available at: FDA Label Database
4. Grimberg A, DiVall S, Polychronakos C, et al. Guidelines for Growth Hormone and Insulin-Like Growth Factor-I Treatment in Children and Adolescents: Growth Hormone Deficiency, Idiopathic Short Stature, and Primary Insulin-Like Growth Factor-I Deficiency. Horm Res Paediatr. 2016;86(6):361-397.