About

This guide provides context for the Cyclophosphamide Dose Calculator, a tool designed to assist healthcare professionals in determining appropriate patient dosing. Cyclophosphamide is a potent chemotherapy and immunosuppressant agent whose dosage depends on the indication, patient body size, and organ function, particularly renal function.

Outputs

The calculator processes patient inputs to generate several key clinical parameters and a final dose recommendation. The primary outputs include:

• Body Surface Area (BSA): Calculated using the Mosteller formula, a standard method for dosing many chemotherapy agents.
• Creatinine Clearance (CrCl): Estimated using the Cockcroft-Gault equation to assess renal function, which is critical for dose adjustments.
• Calculated Dose: The initial dose based on the selected regimen (e.g., mg/m² or mg/kg) and the relevant patient metric (BSA or weight).
• Renal Adjustment: A percentage reduction applied to the dose if the patient's estimated CrCl falls below certain thresholds (e.g., <50 mL/min).
• Recommended Rounded Dose: The final dose, adjusted for renal function and rounded to a practical value for administration (typically to the nearest 10 mg).

How to Use

To use the calculator effectively, gather the following patient information:

1. Patient Demographics: Age and sex are required for the CrCl calculation.
2. Anthropometrics: Height and weight are used to calculate BSA and Body Mass Index (BMI).
3. Renal Function: The most recent serum creatinine (SCr) value is essential.
4. Indication/Regimen: Select the appropriate treatment protocol (e.g., R-CHOP, Lupus Nephritis) or choose a custom dose.
5. Dosing Strategy: Determine if institutional policies require BSA capping or the use of ideal/adjusted body weight for obese patients in CrCl calculations.

Dosing Overview

Cyclophosphamide dosing is highly variable. For oncologic indications like Non-Hodgkin Lymphoma (R-CHOP) or breast cancer (AC), dosing is typically based on BSA (e.g., 600-750 mg/m²). For high-dose conditioning regimens before stem cell transplant, a weight-based approach (e.g., 50 mg/kg) is common. For autoimmune conditions like lupus nephritis, both BSA-based (NIH protocol) and fixed-dose (Euro-Lupus protocol) regimens are used.

Switching

Switching between different cyclophosphamide-containing regimens should only be done under the direction of an oncologist or specialist. Dose conversions are not straightforward due to varying cycle lengths, cumulative dose limits, and combination therapies. When switching from an oral to an IV formulation, dose adjustments are necessary and must be carefully calculated by a qualified professional.

Missed Dose

If a patient misses a scheduled IV cyclophosphamide infusion, the treating physician should be contacted immediately. The decision to administer the dose, reschedule, or skip it depends on the treatment protocol, the patient's condition, and the time elapsed since the missed appointment. It is critical not to double the next dose.

Safety Alerts

Cyclophosphamide carries significant risks that require careful monitoring and management:

• Hemorrhagic Cystitis: Bladder toxicity caused by the metabolite acrolein. Adequate hydration is mandatory. For high-dose regimens (>1 g/m²), co-administration of a bladder-protectant agent like Mesna is required.
• Myelosuppression: Severe bone marrow suppression (neutropenia, thrombocytopenia, anemia) is common. Complete blood counts (CBC) must be monitored regularly.
• Cardiotoxicity: High doses can lead to acute cardiotoxicity and heart failure.
• Secondary Malignancies: There is an increased risk of developing secondary cancers, such as bladder cancer or acute leukemia, years after treatment.

Frequently Asked Questions

What BSA formula is used?

The calculator uses the Mosteller formula: BSA (m²) = √([Height(cm) × Weight(kg)] / 3600).

How does the calculator handle obesity?

The calculator provides options to use actual, ideal (Devine formula), or adjusted body weight for the Creatinine Clearance calculation, reflecting different institutional practices for obese patients. The BSA is typically calculated using actual body weight, but a BSA cap can be applied.

What are the specific renal dose adjustments applied?

The tool applies a 25% dose reduction for CrCl 10-50 mL/min and a 50% reduction for CrCl < 10 mL/min. These are typical but should be verified against institutional guidelines.

Does the calculator provide guidance on Mesna dosing?

No, it only provides an alert recommending Mesna for cyclophosphamide doses greater than 1 g/m². The specific Mesna dosing protocol should be sourced from institutional or manufacturer guidelines.

Can this tool be used for pediatric patients?

This calculator is designed for adult patients. The Cockcroft-Gault formula is not validated for pediatric populations, where formulas like the Bedside Schwartz equation are preferred for estimating renal function.

Why is the final dose rounded?

Doses are rounded to the nearest 10 mg for practical purposes, simplifying measurement and administration while having a negligible impact on clinical efficacy.

What is the difference between the NIH and Euro-Lupus regimens?

For lupus nephritis, the NIH regimen uses a higher, BSA-based monthly dose (e.g., 750 mg/m²), whereas the Euro-Lupus regimen uses a lower, fixed dose (500 mg) every two weeks, which has shown comparable efficacy with a better safety profile in certain populations.

Is it safe to use if the patient has liver problems?

The tool notes that dose adjustments for hepatic impairment are not well-established. Cyclophosphamide is a prodrug activated by the liver, so severe dysfunction can affect its efficacy and toxicity. Clinical judgment is essential, and a 25-50% dose reduction may be considered for severe hyperbilirubinemia.

References

1. CYTOXAN (cyclophosphamide) Prescribing Information. U.S. Food and Drug Administration.
2. Cyclophosphamide - National Cancer Institute. National Institutes of Health.
3. Houssiau FA, Vasconcelos C, D'Cruz D, et al. Immunosuppressive therapy in lupus nephritis: the Euro-Lupus Nephritis Trial, a randomized trial of low-dose versus high-dose intravenous cyclophosphamide. Arthritis Rheum. 2002;46(8):2121-2131.
4. Ginzler EM, Dooley MA, Aranow C, et al. Mycophenolate mofetil or intravenous cyclophosphamide for lupus nephritis. N Engl J Med. 2005;353(21):2219-2228.