Page 1308 - Small Animal Internal Medicine, 6th Edition

1280 PART XII Oncology

which should be discontinued gradually, if at all, because required and the patient should only be observed by the
acute hypoadrenocorticism can develop in animals receiving owner. Owners should be instructed to take their pet’s rectal
VetBooks.ir steroid therapy if the drug is abruptly discontinued. Blood temperature twice daily and to call the veterinarian if pyrexia
develops, in which case the patient is treated as neutropenic
samples for a CBC and serum biochemical profile are
obtained immediately. A urine sample for urinalysis and bac-
intestinal flora but preserve the anaerobic bacteria, which
terial culture may also be obtained, unless the patient is and febrile. ST and fluoroquinolones eliminate the aerobic
thrombocytopenic, in which case cystocentesis should be are an important component of the local defense system
avoided to prevent intravesical bleeding. Two or three sets of because of their ability to produce local antibiotic factors and
aseptically collected blood samples can be obtained at for this reason may be considered over CLAV. In addition,
30-minute intervals for aerobic and anaerobic bacterial cul- ST and fluoroquinolones are active against many pathogens
tures and antibiotic susceptibility tests, although this is isolated from animals with cancer, and they achieve thera-
usually not necessary because the bacterial isolates are quite peutic blood and tissue concentrations and also high intra-
predictable (see following paragraph) and because the results granulocytic concentrations. Recent studies suggest that the
of these tests will not be available for several days. After the use of antibiotics against gram-positive bacteria may shorten
second set of samples for blood cultures is collected (if doing survival time in humans with lymphoma or chronic lym-
so), therapy with an empirical bactericidal antibiotic combi- phocytic leukemia (Pflug et al., 2016), and that the micro-
nation is instituted. The authors use a combination of enro- biome composition predicts risk of sepsis in children with
floxacin (5-10 mg/kg IV q24h) and ampicillin (22 mg/kg IV acute leukemia (Hakim et al., 2018), thus highlighting the
q8h) or ampicillin/sulbactam (30 mg/kg IV q8h) because role of the intestinal microbiome on tumor immunomodu-
most bacterial isolates in such animals are Enterobacteria- lation. Moreover, recent studies suggest that chemotherapy
ceae and staphylococci, organisms commonly susceptible to modifies the intestinal microbiome in some species and
these agents. Once the neutrophil count returns to normal may decrease immunologic response against tumor antigens
and the patient’s condition is clinically normal (usually (Viaud et al., 2013).
within 72-96 hours), the antibiotic combination is discontin- Myelosuppression in dogs may be alleviated through the
ued and the animal is allowed to go home, with instructions use of lithium carbonate (10 mg/kg PO q12h) or, in dogs and
to the owner to administer sulfadiazine-trimethoprim (ST) cats, recombinant human granulocyte colony–stimulating
at a dosage of 13 to 15 mg/kg by mouth (PO) q12h, factor (G-CSF; Neupogen; 5 µ g/kg subcutaneously q24h).
amoxicillin-clavulanic acid (CLAV) at a dosage of 13.75 to Although several studies have reported the beneficial role of
20 mg/kg PO q12h, or enrofloxacin at a dosage of 5 to 10 mg/ G-CSF or granulocyte-macrophage colony–stimulating factor
kg PO q24h for 5 to 7 days. When the patient returns for (GM-CSF) in dogs and cats, it is unlikely that these agents
additional chemotherapy, the dose of the offending agent or will find their way into the clinic owing to their high cost
agents should be decreased by 15% to 20% to prevent an (≈$70-$150/day) and the fact that dogs and cats can mount
additional occurrence. an antibody response to this protein of human origin and
In an unpublished study by one of the authors (GC), the inactivate it; moreover, in dogs with chemotherapy-induced
yield for three sets of blood cultures in dogs with cancer, neutropenia, the activity of endogenous G-CSF is extremely
fever, and normal-to-high neutrophil counts is approxi- high, and neutrophil counts return to normal within 36 to
mately 40%, whereas it is approximately 20% in dogs with 72 hours, the same interval reported for “response” to G-CSF.
cancer, fever, and neutropenia. Isolates in the former group For this reason, G-CSF is typically reserved for patients that
usually include Streptococcus spp., Staphylococcus spp., received accidental chemotherapy overdoses and in which
Enterobacter spp., Klebsiella spp., and Escherichia coli, in the predicted duration of neutropenia is unknown.
decreasing order of frequency. In neutropenic febrile dogs,
the isolates include mainly Klebsiella spp. and E. coli; Staphy-
lococcus spp. is isolated in less than 20% of the dogs. GASTROINTESTINAL TOXICITY
In a recent study (Shaffer et al., 2016) of 57 neutropenic
episodes in 55 dogs undergoing chemotherapy, the preva- Although less common than myelosuppression, gastro-
lence of bacteremia when using 2 sets of blood cultures was intestinal toxicity is a relatively common complication of
12.3% (7/57) and that of bacteriuria was 7.5%. The preva- cancer chemotherapy in pets. From a clinical standpoint,
lence of bacteremia was similar between febrile and afebrile two major types of gastrointestinal complications can
dogs, and most isolates were gram-positive organisms. occur: the combination of anorexia, nausea, vomiting, and
Neutropenic, afebrile, asymptomatic patients can be gastroenterocolitis.
treated as outpatients by discontinuing the drug or drugs Although results of controlled studies are not available,
as described earlier and administering ST (13-15 mg/kg PO nausea and vomiting are not apparently as common in pets
q12h), CLAV (13.75-20 mg/kg PO q12h), or enrofloxacin as they are in humans receiving similar drugs and dosages.
(5-10 mg/kg PO q24h). The patient that is afebrile but has Drugs associated with nausea and vomiting include dacar-
constitutional signs should be considered to be septic and bazine (DTIC), cisplatin, doxorubicin (primarily in cats),
treated as described in previous paragraphs. If the neu- methotrexate, actinomycin D, cyclophosphamide, and
tropenia is not severe (i.e., >1000 cells/µL), no therapy is 5-fluorouracil (5-FU; see Table 77.1).