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Understanding the Risks of Compounded Oral Chemotherapy in Veterinary Medicine

Compounded oral chemotherapy plays a vital role in veterinary oncology—particularly when commercial drugs aren’t available or when precise, individualized dosing is required. However, concerns persist about the accuracy and consistency of compounded formulations, which significantly impacts patient outcomes.

 

Our recent study, published in Veterinary and Comparative Oncology (DOI: 10.1111/vco.13003 ), set out to evaluate just how reliable these formulations are. Specifically, we investigated:

  1. The actual drug content of compounded chlorambucil and cyclophosphamide capsules from multiple veterinary pharmacies.
  2. Performance differences between 503A compounding pharmacies (traditional, patient-specific) and a 503B outsourcing facility (manufactured bulk quantities for practices and hospitals).
  3. Variability both within and between pharmacy batches.

November is National Pet Cancer Awareness Month, a time to raise awareness about animal cancer care across species. As veterinary professionals focus on improving outcomes, Stokes Pharmacy and Epicur Pharma are ensuring the reliability of oncology medications in veterinary medicine.

Explore our unit-dose chemotherapy medications and learn about our new partnership that’s making targeted therapies for dogs more accessible.

Study Design

To ensure a robust analysis, we designed the study with a diverse sample set and clear evaluation criteria:

  • Pharmacies sampled: 9 in total — 8 classified as 503A and 1 as 503B.
  • Batches collected: 2 batches per pharmacy.
  • Capsules analyzed: 68 in total.
  • Assessment criteria: Measured drug content compared to label dose. The FDA allows a ±10% variance from the labeled amount; anything outside this range was deemed unacceptable.

Key Findings

Our analysis revealed several important insights into the accuracy and consistency of compounded chemotherapy capsules:

  1. High rate of unacceptable dosing:
    • 29% of all capsules (20 out of 68) deviated beyond the FDA’s ±10% threshold.
    • This included 12 chlorambucil and 8 cyclophosphamide samples.
  2. 503A vs 503B Accuracy:
    • Cyclophosphamide
      • 503A average deviation: 6.6%
      • 503B deviation: 1.8%
    • Chlorambucil
      • 503A average deviation: 10.4%
      • 503B deviation: 9.6%
  1. Within-batch variability (doses within the same batch):
    • 503A pharmacies: ranged from 0.1% to 51%
    • 503B pharmacy: 2.6% to 7.5%
  2. Between-batch variability (same pharmacy, different batches):
    • 503A pharmacies: ranged from 0.4% to 58.3%
    • 503B pharmacy: 5.0% to 14.8%

Clinical Implications – What does this mean for veterinary oncology practices?

There are several real-world interpretations for veterinary oncologists can take from this study:

  • Dosage inconsistency is common: Nearly 1 in 3 samples fell outside acceptable limits.
  • 503B pharmacies were more consistent: Across both drugs tested, the 503B source provided tighter and more predictable dosing than its 503A counterparts.
  • Within-batch variability is especially alarming: Differences of up to 51% in 503A samples suggest that two veterinary patients receiving capsules from the same bottle could still get drastically different doses.
  • This variability carries risk:
    • Underdosing could reduce therapeutic efficacy.
    • Overdosing raises the risk of toxicity.

As one of the first to make chemotherapy tablets available to veterinarians nationwide, our brands have always been committed to ensuring that every dose delivers the safety and consistency patients deserve. Whether 503A or 503B, both of our brands uphold the highest quality standards so you can be confident in your patient care.

Study Strengths and Limitations

To contextualize these findings, it’s important to consider the strengths and limitations of the study:

Strengths:

  • Real-world sampling from multiple independent pharmacies.
  • Rigorous comparison to FDA-defined dosing standards.

Limitations:

  • Only one 503B facility was included due to a limited number of these types of facilities manufacturing veterinary chemotherapy medications

Bottom Line for Veterinary Oncologists and Clinicians

Ultimately, this study reinforces the significant variability that exists in compounded oral chemotherapy—especially from traditional 503A pharmacies. Whenever possible, clinicians should:

  • Prioritize FDA-approved formulations.
  • Use 503B outsourcing facilities when possible if compounding is necessary, due to their more reliable manufacturing standards.
  • Educate pet owners on the risks and limitations associated with compounded chemotherapy, particularly the potential for dosing inconsistencies. Quality and consistency matter — cutting corners can compromise safety. Choose partners who follow strict standards and are transparent about their processes.

 

Reliable drug delivery is essential for safe and effective cancer treatment. Understanding where your medications come from and how consistently they’re made can make a real difference in patient care.

Because of our commitment to improving patient outcomes, we offer various options through both Stokes Pharmacy and Epicur to ensure you can develop the best treatment plan for your patients’ needs.

From unit-dose chemotherapy tablets and manufactured mechlorethamine to the largest portfolio of targeted therapies for canine cancer through our partnership with Anivive, discover why clinicians trust and choose our medications. 

At Stokes Pharmacy, we take a meticulous approach to compounding, ensuring every product meets rigorous consistency and reliability standards. As an FDA-regulated 503B outsourcing facility, Epicur Pharma adheres to the highest standards of quality and compliance. Backed by more than 150 years of combined experience, our team of chemists and pharmacists applies an exacting process to develop formulations that exceed USP requirements and our own uncompromising internal benchmarks.

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