Misuse of antibiotics part 2: selection in common cases

• Improving antibiotic prescribing practice in companion animals (part one of series)

Part one of this article (VT48.17) discussed general principles of antibiotic stewardship.

Considerations included:

• whether antimicrobial treatment is necessary
• the likely causative organism, patient factors and tissue penetration
• cytology, and culture and sensitivity, to aid diagnosis and refine choices
• avoiding systemic use where possible
• good hygiene and preventive medicine to reduce reliance on antimicrobials
• use of narrow spectrum when possible
• reserved antimicrobials for challenging or resistant infections

In addition to these general principles, the authors suggest particular attention is paid to the following areas to improve antibiotic stewardship in companion animal practice.

It is beyond the scope of this article to give detailed guidelines about antimicrobial prescribing, but a few scenarios are highlighted where antibiotics are frequently misused.

Acute gastrointestinal disease

Antibacterial agents are rarely indicated in acute gastrointestinal (GI) disease in dogs or cats. No evidence exists of benefit in acute GI disease in an otherwise systemically well animal and, in some cases, disruption of the normal flora will delay recovery.

Even in the majority of cases suspected to be of bacterial origin – such as due to Campylobacter, Salmonella or Escherichia coli – no evidence exists that antibacterial treatment will improve outcomes. Prebiotics and probiotics may have value in these cases, and appear to shorten periods of diarrhoea in dogs and cats with acute infectious and non-infectious diarrhoea¹.

Presence of haemorrhagic diarrhoea has historically been considered an indication to instigate antibacterial therapy, with the rationale to reduce the risk of bacteraemia developing from the compromised GI tract. Studies looking at acute haemorrhagic diarrhoea syndrome (formerly known as haemorrhagic gastroenteritis) have found evidence for the causative role of Clostridium perfringens², but no increased risk of developing bacteraemia, compared to healthy dogs, or any increased clinical risk associated with the development of bacteraemia³.

In a prospective study, no benefit in using amoxicillin-clavulanate was found in dogs with haemorrhagic diarrhoea, but without evidence of sepsis⁴. Therefore, the authors would not advocate antimicrobial uses in dogs with routine, non-septic, acute diarrhoea or for the prophylactic protection of animals with haemorrhagic diarrhoea, except in neutropenic parvovirosis.

Antimicrobials should be used in animals showing signs of sepsis, which may be related to GI disease and bacterial translocation. Canine parvovirus will frequently require antimicrobial treatment due to the severity of clinical disease and associated neutropenia. In these severe cases, then, parenteral antimicrobial therapy is likely to be indicated.

A role for antimicrobials in chronic GI disease – such as antibiotic/tylosin-responsive diarrhoea and granulomatous colitis (GC) seen in boxers/French bulldogs – is well documented^5,6. However, the authors would urge readers to remember the importance of diagnostic investigations and other differential diagnoses prior to instigation of antimicrobial treatment in these cases – particularly given antimicrobial resistance to fluoroquinolones is already affecting our ability to treat GC⁷.

Upper respiratory tract disease

Guidelines have been produced by the International Society of Companion Animal Infectious Diseases (ISCAID)⁸, which readers are advised to consult. The majority of cases of canine infectious respiratory disease complex (CIRDC, kennel cough and canine infectious tracheobronchitis) and feline upper respiratory tract disease (cat flu) are thought to be viral in origin, although bacterial agents (such as Bordetella bronchiseptica, Chlamydophila felis and Mycoplasma species) may be involved, either as primary or secondary pathogens.

For cats with short (less than 10 days) or upper respiratory tract signs, serous nasal/ocular discharge, no pyrexia and no systemic signs (such as normal appetite), no indication for antimicrobial therapy exists. Even with the presence of a purulent or mucopurulent nasal discharge, which suggests a bacterial infection, antimicrobial therapy is not indicated unless systemic signs develop.

Symptomatic therapy with NSAIDs may be beneficial. In line with the ISCAID guidelines, the authors would use doxycycline (for 7 to 10 days) as first-line therapy in cats with suspected bacterial upper respiratory tract infection and systemic signs of ill health; it is effective against Bordetella, Chlamydophila and Mycoplasma species. In cases of chronic rhinitis, a complete diagnostic work-up is encouraged.

In dogs with CIRDC, the majority will remain energetic without systemic signs, such as inappetence – and, in these cases, no indication exists for antimicrobial therapy. Symptomatic therapy with NSAIDs may be beneficial.

In cases with systemic signs, but without evidence of pneumonia (on auscultation), doxycycline (for 7 to 10 days) is appropriate empirical treatment. If pneumonia is suspected then further work-up, including radiographs and culture, would be indicated whenever possible.

Lower urinary tract disease

In cats, other than in older animals (greater than 10 years) or any with underlying disease, cystitis is very rarely bacterial in origin. The most common cause is feline interstitial/idiopathic cystitis. Therefore, the authors would not consider the use of antibacterial treatment in these cases unless a bacterial infection was documented (on an aseptically obtained urine sample); the finding of a bacterial lower urinary tract infection in a cat should trigger investigation into an underlying cause.

In female dogs, uncomplicated bacterial cystitis is a common cause of dysuria, haematuria and stranguria. The authors would always advocate obtaining a urine sample for full urinalysis and culture/sensitivity prior to instigating empirical therapy; first-line treatment with amoxicillin or trimethoprim-sulfonamide for seven days is reasonable in an uncomplicated case.

In recurrent or non-responsive cystitis – or cases with systemic signs – culture is always indicated, along with a work-up for underlying causes such as pyelonephritis, urolithiasis, anatomical abnormalities or neoplasia.

In male dogs, uncomplicated bacterial cystitis is rare, so further investigation is always indicated. If antimicrobials are prescribed, consideration must be given to prostatic penetration; amoxicillin (+/− clavulanate) does not adequately penetrate the prostate and is not appropriate. Antimicrobials with good prostatic penetration include trimethoprim-sulfonamide, clindamycin and fluoroquinolones.

Bacterial skin infection

Resistance in staphylococci has been a focus of concern in human and veterinary medicine – MRSA and Staphylococcus pseudintermedius (MRSP) in particular. Therefore, it is sensible that antimicrobial prescription for pyoderma comes under increasing scrutiny.

It is beyond the scope of this article to discuss the treatment of bacterial skin infections in detail, but readers are alerted to articles with suggested guidelines on management of the bacterial skin infections, such as bacterial folliculitis⁹, and the use of systemic antimicrobials in skin infections^10,11. Guidelines are also available about the management of MRSA/MRSP skin infections¹².

Key points to improve and reduce our use of antimicrobials in skin infections are:

• Cytology should be employed to confirm diagnosis and suspected causative organisms.

Culture and sensitivity testing should be performed whenever possible, and always in cases of deep pyoderma; recurrent/relapsing lesion; rod-shaped bacteria on cytology; poor treatment response; life-threatening infection; or when resistance is more likely, such as a previous course of antimicrobial treatment, recent health care contact (owner or patient) or postoperative/nosocomial infections.

• Topical therapy, such as antimicrobial shampoos and sprays, can be used in mild, superficial or focal infections; topical antiseptics can be used alone in mild cases, or combined with systemic therapy to hasten clearance.
• If systemic therapy is required, sufficient dose (upper end of dose range) and treatment length must be employed, with consideration given to achieving owner compliance.
• Underlying causes should always be considered and addressed, as the vast majority of skin infections are secondary to a primary condition, such as endocrinopathy, ectoparasite infection or hypersensitivity.

Acknowledgements

The authors are grateful to Jeanette Bannoehr for her dermatology advice and Sarah Caddy for reviewing the manuscript. The AHT antimicrobial use policy was drawn up by its Infection Control Committee, with guidance from the RVC Infection Control Committee; the authors are grateful to both, and particularly Rosanne Jepson, for allowing reproduction of sections of these policies.

• Some medications recommended in this article are used under the cascade.
• Improving antibiotic prescribing practice in companion animals (part one of series)