Practical Tips for Chemotherapy Administration
Vincristine and cyclophosphamide are commonly used chemotherapy agents primarily used to treat dogs and cats with lymphoma.
Vincristine must be administered via a ‘clean stick’ IV catheter taped securely in place and checked for patency by alternatively flushing (0.9% NaCl) and drawing back blood. Extravasation can have serious consequences but is uncommon when care is taken. Although all chemotherapeutics are myelosuppressive to some degree the myelosuppressive effects of vincristine are generally mild. Haematology should be evaluated 7 days after treatment. If neutrophils are <2x10^9/L at this point treatment should be delayed (if more is due). If neutrophils are <1x10^9/L, or if the patient is pyrexic, broad spectrum antibiotics therapy should also be instituted. If a treatment is delayed, consider dose reducing further vincristine by 10-20% to avoid future delays.
A small percentage of patients experience gastrointestinal toxicity with vincristine administration. There is currently no evidence that this is reduced by premedication with maropitant. Prescribing oral maropitant at standard doses for the patient to have at home if needed in the days following chemotherapy is instead recommended. Gastrointestinal signs that occur more than 5 days after chemotherapy are unlikely to be related to treatment. Inappetance and vomiting can also result from ileus associated with vincristine and ranitidine can help in these cases.
If significant myelosuppressive or gastrointestinal adverse effects do occur following vincristine it is worth contacting a veterinary oncologist to discuss possible causes. Genetic testing for abnormalities in drug metabolism may be recommended (e.g. MDR1 mutation).
Cyclophosphamide can be given orally or IV. Oral administration is simpler but may require compounding to smaller sized capsules as tablets cannot be split or crushed. Gastrointestinal toxicity is uncommon following cyclophosphamide administration and it is not currently recommended to premedicate with anti-emetics. Myelosuppression is expected but rarely severe. Testing haematology 7 days after treatment is recommended and the advice regarding delaying chemotherapy is as for vincristine.
Cyclophosphamide can also cause sterile haemorrhagic cystitis. This is most likely due to accumulation of the irritant metabolite acrolein in the urine causing chronic inflammation. Current recommendations are to administer frusemide 1-2mg/kg IV or SQ alongside cyclophosphamide to encourage evacuation of the irritant metabolites from the bladder. Dogs receiving any type of cyclophosphamide containing protocol should also have frequent access to fresh water and the outdoors for urination to limit the amount of time the urotoxic metabolites are present in the bladder. Frusemide is not administered to cats receiving cyclophosphamide as this species is not prone to developing this side effect.