Chemotherapy Flashcards
What is the mechanism of action of the alkylating agents?
binding of alkyl groups to cellular macromolecules to generate inter or intra-strand crosslinks
Which chemotherapy agents are akylators?
Nitrogen mustards: Mechlorethamine, melphalan, cyclophosphamide, ifosfamide, chlorambucil
Nitrosureas: Lomustine, streptozotocin
Other: dacarbazine, procarbazine
What is the specific mechanism of action of mustargen?
spontaneous hydrolysis –> nucleophilic reactive centers that form DNA crosslinks (i.e. a bifunctional alkylator)
What is a mechanism of resistance to mustargen based on its clinical pharmacology?
Carrier mediated uptake into cells, decreased uptake = resistance
How do you treat mustargen extravasation?
Sodium thiosulfate 2.5% administered through the catheter before it is removed or injected directly into the site at the same volume as mustargen
What is the dose and ROA of mustargen?
3 mg/m2 IV
What is the clinical use of mustargen?
Lymphoma
Does melphalan require metabolic activation?
No - direct alkylating activity
What can block uptake of melphalan and why?
Leucine - melphalan actively transported into cells through amino acid transporters
What is the primary toxicity of melphalan?
Neutropenia and thrombocytopenia
What is the clinical use of melphalan?
Multiple myeloma
What is the dose, ROA, and frequency of administration of melphalan?
0.1 mg/kg PO induction x 14d, then 0.05 mg/kg PO q24h
Alternate for dogs: 7 mg/m2 PO q24h x5d every 3 weeks OR 2 mg/m2 PO q24h x10d then 10d off and repeat
What organ activates cyclophosphamide and how?
Liver – microsomal mixed function oxidases through ring oxidation –> spontaneous and reversible ring opening –> irreversible breakdown
What are the two breakdown products of cyclophosphamide and which is the active compound?
Phosphoramide mustard (active) and acrolein
What is the major dose limiting toxicity of cyclophosphamide?
Neutropenia
What does acrolein cause and how do we mitigate it?
Sterile hemorrhagic cystitis, more common with chronic oral dosing
Treat with furosemide 1-2 mg/kg PO or IV to minimize risk
Mesna to bind
Which neoplasias can we treat with cyclophosphamide and what kind of dosing?
Lymphoma - bolus dosing
Sarcoma and mammary carcinoma - fractionated or metronomic
What is the bolus dosing and ROA of cyclophospamide?
200 - 250 mg/m2 PO or IV
What dose of cyclophosphamide is used for bone marrow ablation?
500 - 750 mg/m2 IV
What is the fractionated dosing and ROA for cyclophosphamide (dog)?
50 - 75 mg/m2 PO for 3-4 consecutive days
Like cyclophosphamide, which other drug requires microsomal mixed function activation in the liver to form an active compound capable of bifunctional alkylation?
Ifosfamide
What is the metabolite produced in the body from ifosfamide and what potential toxicity can it cause?
chloracetaldehyde, neurotoxicity
What are three potential dose limiting toxicities of ifosfamide?
myelosuppresion, nephrotoxicity, damage to the bladder epithelium, neurotoxicity?
What drug must be administered with ifosfamide to avoid severe cystitis?
Mesna
What is the clinical indication of ifosfamide?
treatment of sarcomas
What is the recommended dose of ifosfamide in dogs and cats?
Dogs - 375 mg/m2 IV every 3 weeks
Cats - 900 mg/m2 IV every 3 weeks
*must have saline diuresis
How does chlorambucil enter cancer cells?
Passive diffusion
Which organ is primarily responsible for chlorambucil metabolism?
Liver
What are the major dose limiting toxicities of chlorambucil?
Myelosuppression - granulocytopenia and thrombocytopenia
What are the clinical indications of chlorambucil?
CLL, replace cyclophosphamide in CHOP, Waldenstroms macroglobulinemia, feline small cell lymphoma, metronomic therapy for TCC
What is the dose and ROA for dogs and cats on chlorambucil?
3 to 6 mg/m2 PO q24h
4 mg/m2/d in dogs
2 mg EOD or MWF in cats
20 mg/m2 every 2 weeks in cats
How is lomustine taken into cancer cells?
Passive diffusion - lipid soluble
How is CCNU activated?
spontaneously decomposes to a reactive center to cause DNA-alkylation, DNA-DNA and DNA-protein cross-links at physiologic pH
What is one of the unique features of CCNU as a product of its lipophilicity?
Crosses the blood-brain barrier
Which organ is responsible for lomustine metabolism?
Liver
What are the major dose limiting toxicities of CCNU?
Neutropenia
Cumulative, irreversible thrombocytopenia
Hepatic enzyme elevations and dysfunction (ALT)
Pulmonary fibrosis in cats – rare
When is the nadir of CCNU in cats?
1 to 4 weeks post treatment
What is a medication that can reduce the risk of ALT elevation with CCNU administration?
Denamarin
What is the clinical indication for CCNU in dogs?
Canine lymphoma, MCT, histiocytic sarcoma
What is the clinical indication for CCNU in cats?
lymphoproliferative disorders, MCT
What is the dose of CCNU in dogs? Cats?
Dogs - 70 - 90 mg/m2 PO q3wks
Cats - 40 - 60 mg/m2 PO q4-6 wks or 10 mg/cat q4-6 wks
How does streptozotocin enter cancer cells?
Dependent on GLUT2 transporter uptake
What is the clinical indication of streptozotocin?
Insulinoma
What is the dose and ROA of streptozotocin?
500 mg/m2 IV infusion with saline diuresis every 2 weeks
How is dacarbazine metabolically activated?
Hepatic cytochrome p450
In which species is dacarbazine not recommended and why?
Cats - can’t convert parent drug to prodrug
In which organ is dacarbazine metabolized and excreted?
Metabolized - liver
Excreted - kidneys
What is the major dose limiting toxicity of dacarbazine?
GI toxicity
What is the clinical indication for dacarbazine?
lymphoproliferative diseases in relapse setting, heamngiosarcoma (+ dox, +/- vinc)
What is the dose of dacarbazine single agent? In multi-agent protocols?
Single - 800 - 1000 mg/m2 IV q3wks
Combo - 600 - 800 mg/m2 IV or infusion 200 mg/m2/d IV for 5 days
What unique organ of interest can procarbazine affect?
CNS - rapidly equilibrates with CSF
What is the clinical indication of procarbazine?
treatment of lymphoma in combo with mustargen/CCNU/vinc/pred, hemangiosarcoma
What is the dosing and ROA of procarbazine?
50 mg/m2/d PO q24h x 14d
*no IV administration b/c CNS toxicity with IV dosing
What are tyrosine kinase inhibitors?
Small molecule inhibitors that block receptor tyrosine kinases (RTKs) expressed on the cell surface by competitively inhibiting ATP binding
What are the three TKIs that have been used most commonly in veterinary oncology?
Palladia (toceranib phosphate), masitinib, and imatinib mesylate (Gleevec)