Pharmacology for Cats and Dogs

from The Pharmacologists
September 2023
by ASPET

For a long while, Fluffy had not been feeling quite herself. The 15-year-old
calico was tired, frequently irritable and just didn’t want to play. Fluffy suffered
from chronic kidney disease, and like many older cats with kidney disease, her
blood pressure was too high. The family’s veterinarian was concerned because
hypertension often accelerates kidney deterioration, leading to kidney failure.
He invited Fluffy’s owners to have her participate in an experimental study, which was testing a new antihypertensive treatment for cats.

Comparative Pharmacology
There are about 1,600 drugs specifically labeled for veterinary use, compared to
about 20,000 drugs approved for people (1). In fact, for many animal species,
there are diseases and conditions for which no suitable veterinary drug is
available. Veterinarians, like physicians, may legally prescribe human drugs for
conditions (and species) not approved by the Food and Drug Administration
(FDA). In the veterinary community, off-label prescriptions are called “extra
label” use (1, 2)

The basic principles of drug action are identical across veterinary and human
pharmacology (2). But estimating the optimal dosing regimen for an animal
using a human drug is often little more than guesswork. Each animal species
(and breed) may respond with different pharmacokinetics, pharmacodynamics,
and adverse effects.

Developing a new animal drug follows a similar process as that for human
pharmaceuticals, and the FDA requires the same level and amount of data for
approval. But animal healthcare companies face challenges and complications
that do not occur with human pharmaceuticals (2). Animal species (and breeds)
vary in size, behavior, metabolism, and lifespan. Those factors largely account
for the differences in pharmacokinetics and toxicity profiles. Drug assessment,
particularly regarding side effects, is further complicated because animals
cannot directly communicate with investigators (2).

 

For these reasons, the FDA requires that a veterinary drug label must include
species-specific dosing instructions, and the label may also impose restrictions
that are not part of a human drug label (2).
The review and approval process is handled by the FDA’s Center for Veterinary
Medicine. The agency evaluates and regulates new drugs for seven “major”
species (cats, dogs, horses, cattle, pigs, chickens, and turkeys), as well as all
“minor” species, including fish, ferrets, goats, sheep, birds, rabbits, guinea pigs,
reptiles, zoo animals, wildlife, and bees, among others (1, 2).

Because of the species differences and other variables not present in human
pharmacology, the cornerstone of veterinary medicine is “comparative
pharmacology.” That is, the systematic study of how different species (and
breeds) handle and respond to a drug.

Fluffy Steps Up
Telmisartan (Micardis) is a non-peptide angiotensin II receptor blocker and was
already approved by the FDA to treat people with hypertension. So, the purpose
of Fluffy’s clinical trial was to confirm that the appropriate dose adjustments
had been made for optimal treatment of cats.
Considerable data had already been collected from preclinical animal studies
that had been conducted to support the original human drug approval of
telmisartan. Only two additional issues needed to be addressed.
The FDA requires data from one well-controlled trial showing that the drug
works in the “target animal species” (1). Often, such as in this case, the trial is a

field study, which evaluates how the drug performs when the animal is in its
normal environment (that is, under “field” conditions).
Fluffy’s owners agreed to enroll her in the study. She was one of 221 cats in the
placebo-controlled, double-blind trial (3). Her owners were taught how to
administer the drug solution, which Fluffy slurped daily at home.
Fortunately, Fluffy was in the group receiving telmisartan, and after four weeks
of treatment, her blood pressure dropped significantly to near-normal. The
investigators continued to follow Fluffy for six months. Each day, she took a
maintenance dose of telmisartan, and her blood pressure remained under
control (3)

During development of telmisartan for human use, much of the adverse effect
data and specialized safety test results had already been compiled from
laboratory animals (mainly rodents and dogs), as well as from people. The only
remaining requirement to get regulatory approval of veterinary telmisartan was
data showing that the drug was safe in cats (4).
Typically for a target species safety study, a small number of healthy animals
are used, so that investigators can easily identify species-specific side effects
and establish the safety margin (1). The study must be conducted under Good
Laboratory Practices, and the standard study design recommended by the FDA
is extremely detailed and specific. Drug companies rarely deviate from it (4, 5).
Assessment of drug safety is based on observations of animal behavior, blood
tests, and necropsy, pathology, and histopathology of tissues and organs (1).
The target animal safety study for telmisartan was conducted in healthy,
normotensive cats. After 6 months of dosing, the cats exhibited no troublesome
side effects, and the data were also used to establish the safety margin of
telmisartan in cats. In 2018, the FDA approved veterinary telmisartan (Semintra).
In doing so, telmisartan became the only angiotensin receptor blocker approved
for first-line treatment of hypertension in cats.

Prescription veterinary drugs, like telmisartan, can be dispensed or prescribed
only by a licensed veterinarian. If a drug label’s directions are clear enough for
lay people to administer the drug safely and appropriately to the animal, the
FDA can permit the drug to be available over the counter (1).

But Not Vice Versa
Physicians are discouraged from prescribing veterinary drugs for human use,
even though the practice is legal. Veterinary drugs are often manufactured in
highly concentrated form to accommodate large animals, and the likelihood of
overdosing people is a serious concern (6)

For example, ivermectin was approved in 1981 as a veterinary medicine. It is
widely used to treat worms and other parasites in livestock (6). Subsequently,
ivermectin (Stromectol) was approved to treat river blindness, a parasitic
infection that is prevalent in Africa. The standard treatment to protect people
from acquiring river blindness is a 3- to 12-mg dose given once per year.
The average ivermectin dose in cattle is 80-160 mg. So, people are more likely
to overdose by taking the veterinary formulation. Ivermectin’s overdose effects
include nausea, vomiting, diarrhea, seizures, coma, and sometimes death.
During the COVID-19 pandemic, off-label use of veterinary ivermectin garnered
some media attention, but there was never any data showing it was effective for
treating or preventing COVID-19. Concerned about the public’s health, FDA
officials posted a nowfamous tweet: “You are not a horse. You are not a cow.
Seriously, y’all. Stop it....Using ivermectin to treat COVID-19 can be dangerous
and even lethal” (7)

Encouraging New Animal Drugs
About 70% of American households own pets, totaling nearly 280 million,
including 65 million cats and 85 million dogs (2, 8). Pets have close interactions
with their owners, and they are increasingly treated like members of the family.
Some are comfort or service animals and provide an important wellness
function for people. Consequently, many pets receive a high level of medical
care, which increasingly resembles human healthcare (9).

Despite the increased demand for veterinary drugs, the animal healthcare
industry has had little incentive to invest in new drug development (2).
HealthforAnimals reported that in 2015, it took 6.5 years and $22.5 million to
bring a new veterinary drug to market (8). The profit margin on those drugs
remains far less than the profitability of a new human pharmaceutical (2)
To reduce the financial burden on animal healthcare companies, the FDA’s
regulatory requirements were amended. Greater flexibility is now permitted in
the types of “adequate, well-controlled” trials that are required to establish
efficacy and safety. Also, three or five years of patent exclusivity after market
approval (depending on certain criteria) has been added to offset the time
required to develop a new veterinary drug. Finally, the FDA adopted a phased
review process, which created efficiencies for the reviewers, shortened the
regulatory review time, and increased the likelihood that the veterinary drug will
be approved (2).

New Drugs for Animals
Among the companies that have taken advantage of these incentives is Pfizer
Animal Health, which recently developed maropitant specifically for veterinary
use. Maropitant is a selective neurokinin-1 receptor inhibitor. It binds to
receptors in the chemoreceptor trigger zone and the medullary vomiting center, which receive inputs from the many neurological pathways that trigger vomiting.
Because of this central mechanism of action, researchers hoped that
maropitant would block a broad range of nauseous and emetic stimuli (10)

In a series of studies in laboratory-bred dogs and placebo-controlled field trials
with pet dogs, Pfizersponsored investigators showed that, indeed, maropitant
had broad efficacy. It prevented vomiting induced by chemotherapy, viral
diseases, food and toxin ingestion, intestinal inflammation, opiates, and motion
sickness. The results also showed that maropitant prevented vomiting as
effectively as, or better than, the commercially available antiemetics (2, 10, 11).
Likewise, the target animal safety studies in dogs showed that maropitant is
safer than the other antiemetic drugs used in veterinary medicine. Although
neurokinin-1 receptors are involved in a wide range of physiological and
behavioral responses, the low doses of maropitant used to control vomiting do
not cause adverse effects associated with those other physiological functions
(2).

In 2007, the FDA approved maropitant (Cerenia) as a veterinary prescription
drug to manage vomiting in dogs (10).

Pfizer Animal Health then sponsored another series of studies in cats. Under
both laboratory conditions and in field trials with pet cats, maropitant was
effective in preventing vomiting induced by various noxious stimuli, including
motion sickness (2, 12). The target animal safety studies showed, like dogs, that
there was a wide margin of safety between the effective dose and the
appearance of adverse effects in cats (12). Based on these data, FDA approved
maropitant for cats in 2012.
The comparative pharmacology results from these studies reinforced the view
that animal clinical trials must be species-specific. Maropitant has a higher oral
bioavailability and a longer half-life in cats than in dogs (2). Consequently, the
drug label for cats specifies a dose that is one-half the dose listed on the label
for dogs.

Helping Human Drug Development
Small pharmaceutical companies often lack development resources and
sometimes turn to veterinarians to assist with preliminary efficacy testing of
their drug candidates before launching clinical trials in people. Investigators at
veterinary schools are especially helpful when the target disease or medical
condition cannot be easily simulated in the laboratory. For example, Plex
Pharmaceuticals in San Diego, Calif., recently received Small Business
Innovation Research grants from the U.S. National Eye Institute to test their
novel anti-cataract compounds (13). The protein, alpha-Acrystallin, is a major
component of the eye lens and helps to maintain its transparency. Damage or
aging can cause aggregation of this protein, and protein aggregation in the lens
leads to the formation of cataracts (13).

The Plex lead compound, CAP4196, had produced promising results in treating
other protein aggregation diseases. The Plex researchers developed a topical
eye drop formulation, and they wanted to confirm its efficacy in animals with
cataracts before beginning human clinical trials.
Age-related cataracts are a major health problem in dogs. By age 13, almost
80% of dogs develop cataracts (14). Surgery is the only remedy currently
available.
Plex partnered with researchers at the Univ. of California, Davis, School of
Veterinary Medicine to test the CAP4196 formulation. The UC Davis
veterinarians are recruiting 24 pet dogs for the trial. Each dog must be at least

eight years old and have age-related cataracts. The randomized, placebo-
controlled study will follow CAP4196 treatment at two different doses for 9

months (14)
The Plex researchers hope that the data from the UC Davis trial, along with
other preclinical and regulatoryrequired studies, will be sufficient to gain FDA
clearance to start Phase I clinical trials of CAP4196 in patients with cataracts
(13).

Repurposing a Drug
Sometimes, investigational drugs intended for people are redirected to
veterinary medicine. For example, when Gilead Sciences decided to discontinue
its human clinical trials of rabacfosadine, the small biotech firm, VetDC,
acquired the veterinary rights to the drug (15). In 2019, VetDC licensed the
compound to Elanco Animal Health, a global leader in animal healthcare
products, for further development and commercialization (16)

Rabacfosadine is a nucleotide analog that preferentially targets lymphoid cells
and causes cell death by inhibiting DNA polymerases. One-quarter of all dogs
will be diagnosed with cancer in their lifetime, and lymphoma is one of the most
common types of cancer seen by veterinarians (15, 16).
The efficacy of rabacfosadine in dogs was established in a masked,
randomized, placebo-controlled clinical trial (16). Researchers at several
veterinary schools recruited 158 pet dogs of various breeds. Each dog had been
diagnosed with multicentric lymphoma. For the dog to be included in the trial,
researchers needed to be able to externally measure at least one peripheral
lymph node tumor (16).
Every three weeks, the owners brought their pets to the clinic for a 30-minute
intravenous infusion of rabacfosadine (or placebo solution), for a total of five
doses over 15 weeks (16). Complete or partial responses were observed in 73%
of the rabacfosadine-treated dogs. The compound was not only more effective,
but also required less frequent dosing than human cancer drugs, which are the
only alternatives for dogs with lymphoma (15)
The target animal safety assessment was based on three studies using healthy
beagles. Because of their demeanor and uniform size, beagles are specifically

bred for laboratory studies and toxicology testing. Rabacfosadine was well-
tolerated at the doses used for cancer treatment.

In 2021, the FDA gave full approval of rabacfosadine (Tanovea) as a prescription
drug for the treatment of lymphoma in dogs. In so doing, rabacfosadine became
one of the most comprehensively studied treatment options for dogs with
lymphoma (16).

Veterinary Pharmacology Research
Pharmacologists at veterinary schools conduct a wide range of research, from
comparative pharmacology studies to experimental therapeutics. Sometimes,
their basic research findings serve as the starting point for development of a
new veterinary drug by an animal health company or a new treatment option for
practicing veterinarians. In some cases, those discoveries are also leveraged to
improve human therapeutics.

For example, veterinarians at Cummings School of Veterinary Medicine (Tufts
Univ.) discovered genes in dogs that are biomarkers for canine compulsive
disorder. These genes correlate with an increased incidence of stereotypical
behaviors such as tail chasing (9)

In one series of studies, the Tufts researchers collaborated with colleagues at
Harvard, MIT, and the Univ. of Massachusetts Medical School to search for
behavior-associated genes in Doberman pinschers. Up to 30% of Dobermans
display compulsive behaviors such as incessant licking of flanks or sucking on
blankets (17)

In Dobermans that exhibited compulsive behavior, the researchers found a
mutation in CDH2, a gene on chromosome seven. This canine gene codes for
the same protein that is coded by a corresponding gene on chromosome 18 in
humans. Mutations of chromosome 18 are associated with various human
psychiatric disorders (17)

Researchers in China found this same gene, CDH2, was associated with the
compulsive circling behavior in Belgian Malinois. Interestingly, German
shepherds, a breed similar to Malinois, are also known to circle compulsively
(17).

CDH2 is involved with the development of glutamate receptors, and dysfunction
of glutamate neurotransmission has been associated with obsessive compulsive
disorder (OCD) symptoms in humans (18).

With this in mind, Nicholas Dodman and colleagues at Tufts found that
memantine, an Alzheimer’s drug that blocks brain glutamate, significantly
reduced the compulsive behaviors of dogs (17).

Michael Jenike at McLean Hospital in Belmont, Mass., followed up with a pilot

study in 44 OCD patients who had not responded to SSRIs, the standard-of-
care treatment for OCD (17). Half of the OCD patients were given memantine,

and the other half received standard cognitive behavioral therapy. Only the
memantinetreated patients exhibited significant decreases in their OCD
symptoms (19)

Subsequent clinical trials confirmed the efficacy of memantine, and Tufts
patented memantine as a new treatment for OCD (17).
Until now, investigational psychiatric drugs that showed impressive efficacy in
animal models have often failed in patients with psychiatric disorders. Because
of this lack of predictive correlation, the pharmaceutical industry has reduced
research and development of new psychiatric drugs over the past 50 years
(20).

The results from the Tufts genomic studies in dogs and the therapeutic efficacy
of memantine in both dogs and patients demonstrate the value of canine
compulsive disorder as a valid model of OCD in people (9). It also suggests that
a genomics approach may lead to better and more predictive animal models of
the complicated neural networks associated with psychiatric disorders (20).
Innovative Therapeutics
In addition to genomic and other basic science studies, researchers at
veterinary schools also explore innovative therapeutic regimens for animals. For
example, veterinary researchers are investigating new drug combinations for
osteosarcoma (bone cancer).

Large, long-legged dog breeds are especially prone to develop osteosarcoma,
an aggressive and malignant form of cancer that affects more than 10,000 dogs
in the U.S. each year (21). The annual incidence of bone cancer in people is
much less: about 1,000 cases, mostly children and young adults (21)
Because of the small number of human cases, conducting clinical trials in
people with osteosarcoma is challenging, and there is little incentive to fund
those trials (22). Consequently, no new drugs or treatment regimens for
osteosarcoma have been own immune system can be activated to recognize
and kill osteosarcoma cells. Combining drugs that activate the immune system
in complementary ways could potentiate their cancer-killing effect.
In November 2020, Jellybean’s owners enrolled her in a clinical trial at Tufts
Univ. School of Veterinary Medicine (23). They signed an Informed Consent
Form and were trained to administer the drugs. Every day, they stuffed three
pills in Jellybean’s favorite chickenflavored treats. By Christmas, Jellybean’s
tumors had begun to shrink, and they haven’t come back. Now five years old,
Jellybean walks with ease, as if she had never had metastatic cancer (23).
The drug combo that Jellybean received was toceranib (Palladia), losartan, and
ladarixin.

Toceranib is a tyrosine kinase receptor inhibitor approved for treating dog
tumors. It directly kills tumor cells. Toceranib is also an angiogenesis inhibitor
and decreases the blood supply to the tumor.
Losartan is an angiotensin II receptor blocker approved to treat hypertension.
But at a tenfold higher dose, it also blocks the recruitment of immune cells that
stimulate tumor growth (23, 24) developed in over 35 years. On the other hand,
the high incidence of osteosarcoma in dogs offers an opportunity to accelerate
this research and drug testing (22, 23).

Ladarixin is an experimental (unapproved) inhibitor of IL-8 receptors. It inhibits
the recruitment of neutrophils.
Jellybean, a two-year-old Labrador-retriever mixed breed was diagnosed with
bone cancer in her hind leg (23). The standard treatment is amputation followed
by four rounds of chemotherapy with carboplatin. But despite amputation and
chemotherapy, metastases to various organs occur in

90% of dogs (23)

Jellybean’s case was typical. After undergoing amputation and chemotherapy,
her cancer quickly spread to her lungs. A dog’s average survival time is about
two months after metastases are detected (23) But Jellybean had another
treatment option.
Evidence has accumulated from both laboratory studies and human clinical
trials that an individual’s
The complementary mechanisms of these three drugs enhance the immune
system’s ability to target and kill tumor cells.
The response of Jellybean and other dogs to the three-drug regimen was
encouraging. But delaying treatment until after amputation and completion of
chemotherapy permitted residual tumor cells to become drug-resistant and
metastasize (23)

The Tufts researchers thought that the drug combo would work even better if
treatment began earlier (23). In a follow-up study, which is ongoing, the
researchers administer the toceranib-losartan-ladarixin regimen prior to
amputation. At this early stage, any residual tumor cells are assumed to be more
vulnerable to attack by immune cells. Hopefully, the drug combo will prevent the
cancer from spreading to the lungs and other organs.
In parallel with this trial, academic researchers at Children’s Hospital Colorado
launched a Phase I clinical trial (NCT03900793). This ongoing dose-escalation
study is recruiting 41 children and young adults who suffer from resistant or
recurrent osteosarcoma. The patients are receiving losartan and sunitinib
(Sutent), a tyrosine kinase inhibitor that has been approved for human use and
is analogous to the veterinary-approved toceranib.

Pet Clinical Trials
As these examples suggest, researchers now recognize that pet dogs and cats
have advantages over lab-raised animals for assessing human drugs. Pets are
exposed to much of the same environment as humans. They share the same
homes, consume the same water and foods, and are exposed to a number of
the same hazards (21-23, 25)
Because of their high level of medical care, the pets’ detailed medical records
are often available (25) Unlike humans, there are fewer medical confidentiality
concerns (e.g., HIPAA regulations), making data sharing easier (22)
Cats are 90% genetically identical to humans, and dogs are 95% identical. Not
surprisingly, similar genetics and a similar living environment make pets and
their owners vulnerable to many of the same health risks (26). Like humans,
cats and dogs naturally acquire diseases, such as obesity, diabetes, heart
disease, and cancer (23, 26). Laboratory rodents, on the other hand, must be
manipulated to induce a disease condition, and they have proven to be less
reliable in predicting human responses to drug treatment (22, 23).
For example, only 15% of cancer drug candidates survive to Phase III after
successful preclinical testing in laboratory animals. Only half of the cancer
drugs in Phase III trials will be approved for clinical use, giving an overall
success rate of less than 8% (20).

Researchers now know that many naturally occurring cancers that affect dogs
and cats (including osteosarcoma, breast and prostate cancers, nonHodgkin’s
lymphoma, head and neck cancer, and melanoma) share features with human
cancers (23, 25). Those animal tumors not only look the same as human tumors
microscopically, but also mutations in the same genes often drive emergence
and spread of the cancer (22). Given those similarities, it is perhaps not
surprising that pet and human cancers seem to respond to treatments in similar
ways (23)

Cancer trials in pets also provide data that have fewer uncontrolled variables
that might interfere with interpreting drug efficacy. Cancer patients typically
must fail the standard of care (often chemotherapy) before enrolling. Also,
because it is considered unethical to give a cancer patient only an experimental
drug (that might not work), they are usually given the best-known effective
treatment, in combination with the experimental drug (22)

By contrast, pets can enroll in an animal clinical trial without having their
immune system already compromised by earlier (failed) treatments and without
an accompanying standard-of-care drug. This makes the efficacy data easier to
interpret.

Over the past decade, great progress has been made in accumulating
comparative genomic data, fostering collaboration between veterinarians and
oncologists, and attracting funding for pet clinical trials.

The Comparative Oncology Program
About four million dogs in the U.S. are diagnosed with cancer every year, and
this large pool of pets promises to speed development of cancer treatments
that will benefit both them and their owners (21). This approach is called
comparative oncology (25).

In 2003, the U.S. National Cancer Institute (NCI) launched the Comparative
Oncology Program. Under the Program, NCI works collaboratively with
academic researchers at 20 veterinary schools in the U.S. and 2 in Canada to
study the biology of a variety of cancers and to assess novel treatments (25).
The Program is now funded under the White House’s Cancer Moonshot Initiative
and oversees dozens of pet clinical trials (21, 22).

NCI and the participating academic veterinary clinics collaborate to design and
implement these pet clinical trials, which closely mimic the procedures that are
used to recruit, enroll, and treat people in a clinical trial.

To participate, the pets must meet strict enrollment criteria. Their owners must
sign an Informed Consent Form and follow the protocol procedures stipulated
for their pet. Board-certified veterinary oncologists at the veterinary schools are
responsible for conducting the trial and monitoring the pets’ health (25)

The results from these cutting-edge trials give researchers valuable information
on investigational drug pharmacokinetics, pharmacodynamics, dose strength,
dosing schedule, biomarkers, toxicity, and various histology endpoints. This
comparative oncology information is then used to design additional trials to
establish the compounds’ efficacy and safety. Those results will hopefully
benefit both animals and people with cancer (25).

Cutting-Edge Trials

For example, investigators at Case Western Reserve Univ. discovered BG34-
200, a 200-k Dalton glucose polysaccharide that was derived from oats. BG34-
200 dramatically increases the level of immune factors (i.e., gamma-interferon

and TNF-alpha) at the tumor site. In addition, the compound mobilizes tumor-
reactive T cells systemically (27). Unlike many chemotherapy drugs, BG34-200

can be prepared in both oral and injectable formulations.

In laboratory mice that have been manipulated to express advanced melanoma,
BG34-200 significantly inhibited tumor growth and improved survival (28).
These results suggested that immunotherapy with BG34200 might be an
effective alternative for patients with advanced melanoma, that is, melanomas
that have failed to respond to current standard-of-care treatments (28)
To confirm the compound’s efficacy and provide greater justification for human
clinical trials, the NCI Comparative Oncology Program is sponsoring a study at
the Univ. of Pennsylvania: “Pilot assessment of BG34-200 in spontaneous
canine cancers” (COTC029). Up to 10 dogs weighing more than 15 kg are being
recruited for the trial. Each dog must be diagnosed with an initial or recurrent
solid tumor larger than 2 cm.

This pilot study will evaluate the safety of BG34-200, as well as its ability to
stimulate the dogs’ immune system, to recognize cancer cells and attack them.
In addition to malignant melanoma, the study will also explore the compound’s
efficacy against other tumor types, such as mammary tumors, soft tissue
sarcoma, and osteosarcoma.

Each week during the six- to seven-week treatment period, pet owners will
bring their dogs to the Univ. of Pennsylvania clinic, where veterinary oncologists
will measure the tumor size and assess drug-related side effects.
Recognizing the great promise of immunotherapy drugs to treat cancer, NCI
established a network of five veterinary schools in 2017 to conduct clinical trials
specifically of cancer immunotherapy drugs in pet dogs (29). In 2022, five
additional academic sites were added. Currently, the cutting-edge
immunotherapy treatments being investigated at these ten sites include drug
combinations to treat dogs with lymphoma, osteosarcoma, and
hemangiosarcoma (29).

To ensure the quality and accessibility of data from each dog trial conducted by
this network, the School of Veterinary Medicine at the Univ. of Pennsylvania
was designated as the Data Coordinating Center. The Center compiles data
from all of the participating veterinary academic sites, ensures consistency in
data collection across sites, harmonizes and integrates the data, and enables

researchers to identify important common signals. This aggregated and high-
quality data will allow both veterinarians and physicians to make evidence-
based decisions when selecting treatment plans for their cancer patients (29).

Pet Prominence
The first wave of veterinary schools in the U.S. arose in the 1860s at land grant
colleges (30). Because the curriculum emphasized agriculture, engineering, and
the “practical arts,” the land grant colleges were located in predominantly rural
agricultural areas. Consequently, veterinary students at these schools had little
exposure to the centers of medical education, which were largely contained
within universities in urban areas (30).

The main focus of veterinary education, practice, and research in the land grant
colleges was related to the health and well-being of livestock and horses (31)
Veterinary students consisted mainly of farm-reared boys, because of their
intimate knowledge of farm animals (30). Companion animals were not
considered a priority for either veterinary education or research (31)
Farm experience was the dominant admissions criterion, and there was a strong
bias against admitting veterinary students from urban areas (30). At some
veterinary schools, applicants had to validate their farm proficiency by
harnessing work horses, backing two-wheeled wagons with a tractor, and
placing milking machines on cows (32). Given this situation, few women were
admitted to veterinary schools in the 19th and early 20th centuries (32).
The emergence and evolution of veterinary pharmacology paralleled changes in
society and attitudes toward animals (6). In the mid-20th century, veterinary
medicine shifted from a predominantly large animal practice to increasing
consideration of companion animals. As pets became more integral family
members, their health became a greater concern, and pet owners were more
willing to invest in pet care (6, 31).

In 2022, spending on veterinary care reached $35 billion (9, 33). Much of this is
spent on prescription and over-the-counter drugs (9). The median lifetime drug
expenditures for a dog are $5,154 and for a cat are $5,325 (8).

Increased pet owner demands encouraged more veterinarians to specialize in
companion animal care, which in turn, drove veterinary college faculties to,
slowly but steadily, increase coursework on small animal medicine (31). At the

same time, thanks to the passage of Title IX in 1972, the barriers to acceptance
of women students into veterinary schools were relaxed (31)
The number of female veterinary students increased dramatically, and this trend
continued over the following decades. By 2000, the gender ratio of veterinary
students settled at

80% women and 20% men. As a result, over half of

practicing veterinarians are now women (31).

Many of those women are drawn to veterinary positions in pet hospitals or
group veterinary practices in urban areas, both of which cater mainly to cats
and dogs. Large animal veterinary medicine is still needed, and those
veterinarians must comply with special regulations regarding drugs prescribed
for foodproducing animals, such as cattle and chickens, and performance
animals, such as racehorses. But that’s another story.

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Rebecca J. Anderson holds a bachelor’s in chemistry from Coe College and
earned her doctorate in pharmacology from Georgetown University. She has 25
years of experience in pharmaceutical research and development and now
works as a technical writer. Her most recent book is Nevirapine and the Quest
to End Pediatric AIDS. Email rebeccanderson@msn.com