By Kim Freeman, DVM, DACVIM (Oncology)
Veterinary Cancer & Surgery Specialists
Prescribing of chemotherapy drugs is a daily part of my job as an oncologist. As with any pharmaceutical agent, part of prescribing these drugs requires knowledge of the risks and side effects associated with chemotherapy. Unique to many other drugs commonly used in practice, chemotherapy without adequate knowledge of the risks and side effects or without appropriate monitoring can result in life threatening complications. This is true for both oral and intravenous chemotherapy drugs. There seems to be a misconception that oral chemotherapy is safer than intravenous chemotherapy. Ok, yes, there is no risk for extravasation injury and there are fewer drug handling precautions, but in terms of patient risk, oral drugs should be prescribed with equal precaution as IV chemotherapy. Oral drugs can be myelosuppressive, GI toxic, hepatotoxic and nephrotoxic to the same or greater degree than IV chemotherapeutics. Routine lab monitoring of CBCs at a minimum and often chemistry profiles too are indicated on a routine basis to watch for trending or acute myelosuppression seen with all chemotherapy drugs and, liver or renal toxicity seen with some chemotherapy drugs. It would be unfortunate to have a patient die of sepsis secondary to chemo induced myelosuppression because you weren’t regularly checking CBCs. This can happen with chlorambucil, Mephalan, lomustine, and cyclophosphamide to varying degrees. Understanding safe handling practices, drug nadirs, and toxicities are important in a successful outcome and reduced risk for complications.
Dosing chemotherapy appropriately can be challenging in veterinary medicine, since many of our patients are small and many drugs are made for human use. Drug compounding has been incredibly helpful to veterinary practitioners both in regards to drug dosing and cost savings. The FDA has been trying to improve regulatory controls over compounding, making it more difficult to legally prescribe compounded drugs to patients. However, the FDA may have good cause for this and maybe we should listen. There is concern that compounded formulations of drugs vary in potency from FDA approved products. Compounding due to cost alone is not really a legitimate reason to have chemotherapy compounded.
In JVIM, 2016; 30: 242-246, JH Burton, the investigator found that the potency of lomustine from 5 different compounding pharmacies ranged from 50- 115% of the labeled concentration. This finding suggests that you could easily over- or underdose a patient. Underdosing has no life threatening consequences other than the treatment might not be effective. Overdosing a drug like CCNU could be devastating and life threatening. Does this mean that we should stop compounding CCNU? Maybe not. It comes in 5 mg, 10 mg and 40 mg capsule sizes from the manufacturer which is held to a higher level of quality control (we order CCNU through Amatheon). I use CCNU as an example, but in reality, this should apply to any chemotherapy drug being prescribed. Know your dose. Know the side effects. Know what monitoring is necessary. Use commercially available compounds when available. Get to know your compounding pharmacist well and ask about their quality controls in place to ensure that you and your patient are getting what you ask for. All of this aids in client education, minimized risk to the patient, client support of your treatment plan and ideally, lower stress for everyone and an improved successful outcome.
If you have any questions about safe handling and administration of chemotherapy, don’t hesitate to call me.