The Forteo (teriparatide) Dosing Calculator is a clinical support tool designed to help healthcare professionals and patients track the duration of therapy. Its primary function is to calculate the cumulative days of treatment used against the recommended 24-month (730-day) lifetime maximum.

By inputting a start date and accounting for any treatment interruptions, the calculator provides a clear summary of the therapy timeline, helping to ensure treatment duration adheres to safety guidelines established in the prescribing information.

• Projected Therapy Completion Date: An estimated date when the 730-day lifetime limit will be reached, assuming continuous daily administration from the "Calculation Date".
• Days of Therapy Used: The net number of days the patient has been on teriparatide therapy, calculated as the total time from the start date minus any specified interruption periods.
• Days of Therapy Remaining: The number of days left within the 24-month lifetime limit (730 minus Days Used).
• Percentage of Lifetime Dose Completed: A visual representation of how much of the total allowable therapy has been administered to date.

1. Enter Therapy Start Date: Input the exact date the patient first started taking Forteo (teriparatide). This is a required field.
2. Confirm Calculation Date: This field defaults to the current date but can be changed to project outcomes for a future date.
3. Add Treatment Interruptions (Optional): If the patient stopped taking the medication for one or more consecutive days, click "+ Add Interruption" and enter the start and end dates for that period. The calculator subtracts these days from the total treatment duration. Add each distinct interruption period separately.
4. Calculate: Click the "Calculate" button to see the therapy summary.

Standard Dose: The recommended dosage of Forteo is 20 mcg administered once daily by subcutaneous injection in the thigh or abdominal wall.

Lifetime Limit: The cumulative use of Forteo and other teriparatide analogs for more than 2 years (24 months) during a patient's lifetime is not recommended. This is due to a dose-dependent increase in the incidence of osteosarcoma (a bone cancer) observed in animal studies. The calculator is based on a 730-day treatment limit to align with this guidance.

Forteo is an anabolic agent that stimulates new bone formation. After completing the maximum 24-month course, the bone density gains may be lost over time if not followed by another therapy. Therefore, it is common clinical practice to transition patients to an antiresorptive agent (such as a bisphosphonate or denosumab) to maintain or further increase bone mineral density. The decision to switch therapies should be made by a healthcare professional based on the individual patient's clinical situation and risk factors.

If a dose of Forteo is missed, it should be administered as soon as it is remembered on that same day. However, a patient should not take more than one injection in the same day. If the entire day is missed, the patient should skip the missed dose and resume their regular once-daily dosing schedule the next day. Do not double the dose to make up for a missed one.

BOXED WARNING: OSTEOSARCOMA RISK
Teriparatide has been associated with an increased incidence of osteosarcoma in rat studies. Because of this potential risk in humans, the cumulative use of Forteo for more than 2 years during a patient's lifetime is not recommended.

Contraindications: Forteo should not be used in patients with:

• Pre-existing hypercalcemia
• Severe renal impairment
• Paget's disease of the bone
• Unexplained elevations of alkaline phosphatase
• Pediatric and young adult patients with open epiphyses
• Prior radiation therapy involving the skeleton
• Bone metastases or a history of skeletal malignancies

Why is there a 24-month (730-day) lifetime limit for Forteo?
The limit is a safety precaution based on preclinical studies in rats that showed a risk of osteosarcoma with long-term, high-dose exposure. The 24-month cap is intended to mitigate this potential risk in humans.

Can I restart Forteo later in life if my first course was short?
The 24-month limit is cumulative over a patient's entire lifetime. For example, if you used Forteo for 6 months, you would have 18 months remaining for potential future use, but retreatment decisions must be made by a healthcare provider.

What qualifies as a "treatment interruption"?
Any continuous period where the daily injection was not taken should be entered as an interruption. This could be due to travel, illness, side effects, or a temporary pause advised by a doctor. The calculator requires both a start and end date for the interruption period.

The projected completion date is in the past. What does this mean?
This indicates that, based on your start date and interruptions, the 730-day lifetime limit has already been reached or exceeded. Therapy should be discontinued in consultation with your healthcare provider.

Does this calculator account for leap years?
Yes, the calculation is based on the actual number of days between the specified dates, which automatically accounts for leap years.

Can I use this calculator for other teriparatide products (e.g., Bonsity®)?
Yes. The 24-month lifetime limit applies to the active ingredient, teriparatide, not just the Forteo brand. The calculator can be used to track the cumulative duration for any teriparatide therapy.

How is the net therapy duration calculated?
The tool first calculates the total number of days between the Therapy Start Date and the Calculation Date. It then subtracts the total number of days from all specified interruption periods to arrive at the net "Days of Therapy Used."

1. FORTEO® (teriparatide) injection, for subcutaneous use. Prescribing Information. Eli Lilly and Company. Accessed via FDA.gov.
2. Eli Lilly and Company. Forteo (teriparatide) Official HCP Website. www.forteo.com.
3. Forsteo (teriparatide). Summary of Product Characteristics (SmPC). European Medicines Agency (EMA). www.ema.europa.eu.
4. Eastell R, Rosen CJ, Black DM, Cheung AM, Murad MH, Shoback D. Pharmacological Management of Osteoporosis in Postmenopausal Women: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2019;104(5):1595-1622. doi:10.1210/jc.2019-00221.