Bacterial infections: Resistance isn’t futile

Primary health-care providers in veterinary and human medicine face the same problem when it comes to client expectations.

Primary health-care providers in veterinary and human medicine face the same problem when it comes to client expectations.

“Various studies suggest human patients and their primary health providers may not be on the same antibiotic page,” says Dan Carey, DVM, a veterinarian with Bayer Animal Health. “Primary care providers tend to think most patients expect something to treat their ailment, while patients tend to be the converse: ‘If I don’t need it, just help me feel better somehow.’”

What’s his advice? Clinicians should ask clients what their expectations are; then as educators, take the opportunity to explain the options.

“We do not have to reflexively reach for a seemingly innocuous antibiotic just so the client has something to take,” Dr. Carey says. “But the client needs to know what we have chosen, why it was selected, and how it is properly used to get the expected response.”

Heather Loenser, senior veterinary officer for the American Animal Hospital Association (AAHA), agrees. She wants veterinarians to understand the seriousness of antimicrobial resistance (AR).

“In an effort to control AR, antimicrobial use should be confined to appropriate clinical indications,” says Dr. Loenser, adding veterinarians should establish a definitive diagnosis whenever possible and avoid empirical use.

“Practitioners should strive to rule out viral infections, parasitism, mycotoxicosis, nutritional imbalances, and other ailments that will not respond to antimicrobial therapies,” she says.

Many times, antimicrobial therapy just isn’t the answer. It’s not indicated in most viral upper respiratory infections (e.g. feline herpesvirus or calicivirus and canine influenza), which are not suspected to be complicated by secondary bacterial infection, according to Loenser.

For example, instances where antimicrobials are not indicated include cases of pancreatitis in dogs and cats, which do not have a bacterial component, and most cases of feline lower urinary tract disease also do not involve bacterial infection.

“Many pet caregivers, especially parents of young children, understand how physicians are reluctant to treat fevers, ear infections, and colds with antibiotics, for the same reasons—namely antimicrobial resistance,” she says. “Reminding [them] of the consequences of creating bacteria in their pet, their home, and local environment that are difficult to treat can be compelling.”

She also recommends educating the entire staff “from front to back” to deliver a unified message to clients who come in demanding antibiotics.

Far from a new issue, AR has been looming since the first antibiotics were developed, Carey says.

“Sir Alexander Fleming predicted the clinical implications when he discovered penicillin in the 1920s,” he adds. “Bacteria have always had enough susceptibility variation that some may survive and propagate a resistant subpopulation when faced with naturally occurring antibacterial compounds or human-made drugs. It has become increasingly important clinically, as continued selection pressure has allowed unaffected phenotypes to survive.”

While certain bacterial species have always been unaffected by some antibacterial drugs, this type of resistance is not the real concern. The problem lies in the species that were once susceptible to specific antibiotics, but have lost that vulnerability, according to Carey.

“The development of new classical antibacterial molecules for veterinary medicine has virtually stopped,” he says. “We have what we are going to have until some breakthroughs occur. This situation makes the long-existing reality of resistance a very topical [and very real] problem for clinicians, clients, and patients.”

Breaking old habits, considering alternatives

Jane Sykes, PhD, BVS, an academic administrator and professor of medicine and epidemiology at the University of California, Davis, offers a list of questions companion practitioners should ask themselves before reaching for antibiotics:

  • Is this a condition that might not require antibiotics for successful treatment?
  • If a bacterial infection is likely, what is the underlying cause, and how can I address it so repeated bacterial infections do not occur?
  • If a bacterial infection is likely, what is the most appropriate empiric antibiotic, given the site of the infection, and what is the shortest duration of treatment that might cure the infection?
  • Is there an opportunity to do culture and susceptibility testing before starting empiric treatment, in case this is a resistant infection, and what’s the best sample for testing?

“Companion animal practitioners can work toward the need to control AR by considering alternatives to antibiotics for treatment,” Dr. Sykes says.

But the axiom that old habits are hard to break rings even louder when met with the steadfast habits of both practitioners and clients.

Carey recalls advice an elder physician offered to a friend about her respiratory problem. The physician told her the issue would improve in a week if it was left to run its course or in seven days if an antibiotic was prescribed to treat it.

“This very simple statement sums up the challenge we face as clinicians: knowing the difference between a responsive bacterial infection and a primary, nonbacterial disease,” he says.

Knowing is only a first step; the entire process isn’t so easily followed in reality.

“Clients often balk at the cost of diagnostics,” Carey says. “When allowed, diagnostics are not always, well, diagnostic. And regardless of the diagnostic outcome, clients often want something to give their pet.”

There is no shortage of cases when other nonantibiotic drugs might be as effective at helping patients feel better while letting immunologic defense systems do their work. Symptomatic support with bronchodilators, analgesics, antipruritics, decongestants, pre/probiotics, and nutritional support, also can provide benefit without the risk of selecting for resistance, according to Carey.

“We must always remember that our patients have thousands of bacteria living in them all the time,” he says. “Some are potential pathogens held in check by the system. Using any antibacterial drug has the potential to select for a resistance strain of the innocent bystander that can later become a full-blown pathogen with a nasty resistance pattern on the antibiogram.”

Carey is among many experts who refer to the International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for antibacterial stewardship, which are based on scientific information. These guidelines can be useful in helping decide when and when not to use antibacterial drugs.

“We are responsible for the proper drug choice,” Carey says. “The client is responsible for compliant use. Compliance is dependent upon the client understanding the need for the drug and the importance of completing the prescribed protocol. Inadequate antibacterial dosing is a recipe for bacterial resistance.”

Education is fundamental to compliance, but so is ease of use. For instance, a drug that can be administered in-clinic stands a much better chance of compliant use, while the dosage form—liquids are typically easier in cats than pills and considerably easier for owners to administer—needs to match not only the patient but also that of the client, according to Carey.

Specific considerations

If practitioners do begin antibiotics, Sykes recommends starting with a short course—three to five days for urinary tract infections (UTIs), seven to 10 days for respiratory, and one to two weeks for skin. After 24 to 48 hours, consider an “antibiotic time-out” to figure out whether there is a response to treatment, if antibiotics can be stopped, or if there are other treatments that might be more effective.

She also recommends knowing the difference between subclinical bacteriuria and a urinary tract infection, and how they should be treated.

“Subclinical bacteriuria is bacteria in the urine without the presence of signs of lower urinary tract disease,” she says. “A diagnosis of bacterial UTI requires the presence of dysuria, hematuria, or stranguria. Subclinical bacteriuria is common, especially in older animals, and often does not require or respond well to antibiotic treatment.”

Veterinarians should consider not culturing the urine of animals who don’t have signs of lower urinary tract disease and not treating animals with subclinical bacteriuria unless a systemic bacterial infection is suspected, she adds.

She advised educating pet owners through discussion of problems with antibiotic-resistant bacteria in pets, how treatment only selects for resistant bacteria when the underlying cause is not addressed, and how some infections now are virtually untreatable or require intravenous antibiotics.

Practitioners can instruct clients as follows:

  • The overwhelming majority of cats with lower urinary tract signs do not have bacterial infections; time or analgesics and a workup for stones is a better strategy than treatment with antibiotics
  • Almost all adult dogs with chronic nasal discharge (greater than 10 days) do not have a problem that can be treated successfully with antibiotics. An early diagnostic workup to look for foreign bodies, fungal infection (nasal aspergillosis), and nasal tumors could dramatically improve the long-term outcome compared with trying different courses of antibiotics for a secondary bacterial infection
  • Most dogs with kennel cough and cats with acute (less than 10 days) upper respiratory tract disease do not need antibiotics

AR is a big problem that demands attention, says Sykes, adding reports of resistant bacterial infections in her hospital have increased progressively over the last five to 10 years.

“We are increasingly facing situations where we only have parenteral treatment options with drugs that are potentially toxic or expensive, such as aminoglycosides or carbapenems (meropenem),” she says. “Companion animal practitioners must be proactive and responsible in their approach to antibiotic use, otherwise we will be faced with watching individual animals suffer or even worse, die in the face of antibiotic-resistant bacterial infections despite our very best efforts in that individual situation.”

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