Pharmacology of drugs used in autoimmune dermatopathies in cats and dogs: A narrative review

Immunosuppressive drugs are the mainstay of treatment for many feline and canine autoimmune skin diseases, either as monotherapy or in combination with other drugs. Treatment with these drugs is often lifelong and may have long-term consequences on the affected animal's overall quality-of-life. Clinicians need to understand the pharmacology of immunosuppressants in planning and executing the treatment regimen for the best possible clinical outcome, as well as reducing the risk of adverse effects. This review paper will focus on the mechanism of action, pharmacokinetics and pharmacodynamics, clinical uses and adverse effects of immunosuppressive drugs used to treat autoimmune dermatoses in cats and dogs. These include glucocorticoids, ciclosporin A, azathioprine, chlorambucil, mycophenolate mofetil, oclacitinib and Bruton's tyrosine kinase inhibitors.

Validation of laser doppler flowmetry to measure dermal blood flow of the pinnae in dogs with pinnal alopecia

BACKGROUND

Laser Doppler flowmetry (LDF) is a noninvasive method of measuring regional blood flow in humans. However, this method has not been widely applied to measure blood flow in dogs.

HYPOTHESIS/OBJECTIVES

We hypothesised that LDF can measure changes in blood flow in canine pinnae accurately. The objectives were to determine whether LDF could accurately detect dermal blood flow changes in canine pinnae caused by haemodynamic drugs and characterize the dermal blood flow in dogs with pinnal alopecia.

ANIMALS

Sixteen laboratory-owned healthy dogs, 25 client-owned healthy control dogs and six dogs with pinnal alopecia suspected to be secondary to ischaemic dermatoses.

MATERIALS AND METHODS

Clinical doses of the haemodynamic drugs atropine, medetomidine and dibutyryl cyclic adenosine monophosphate (dBcAMP), as well as topical dBcAMP, were administered to healthy beagles. Subsequently, an LDF apparatus was attached to the pinnae to analyse changes in dermal blood flow. Finally, LDF was used to measure auricular dermal blood flow in dogs with pinnal alopecia compared to healthy dogs.

RESULTS

Dermal blood flow increased after atropine injection, during dBcAMP infusion and after topical dBcAMP ointment application, and decreased after medetomidine injection. Auricular dermal blood flow (in mL/min/100 g tissue) was significantly (p < 0.05) lower in dogs with pinnal alopecia than in healthy dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Laser Doppler flowmetry is useful for measuring dermal blood flow in canine pinnae; it can be a noninvasive method to monitor ischaemic conditions of dog skin.

Canine ischaemic dermatopathy: a retrospective study of 177 cases (2005-2016)

BACKGROUND

Ischaemic dermatopathy encompasses a poorly understood subset of canine diseases that share similar clinical and histological features. Very little information is currently available regarding population characteristics, progression and outcome.

HYPOTHESIS/OBJECTIVES

This study aimed to describe the clinical features and therapeutic outcomes of ischaemia dermatopathy, excluding familial dermatomyositis, using cases diagnosed by histopathological analysis.

ANIMALS

One hundred and seventy-seven cases submitted for histopathological analysis between 2005 and 2016 met inclusion criteria, of which 93 had complete medical records available.

METHODS AND MATERIALS

Both records and pointed surveys were used to retrieve information. Scoring systems were created to subjectively evaluate clinical outcomes and likelihood of a vaccine association.

RESULTS

Of 177 cases, toy and miniature poodles, Chihuahuas, Maltese, Yorkshire terriers and Jack Russell terriers were significantly over-represented (P < 0.001). Of the 93 cases for which historical data were obtained, median age at skin biopsy was five years (0.42-13 years) and median body weight was 7.3 kg (range 1.32-50.3 kg). The condition in 45 dogs (48.3%) was found likely to be associated with vaccination. Younger ages (P = 0.011) and higher body weights (P = 0.003) were positively correlated with greater likelihood of vaccination. Body weight <10 kg (P = 0.0045) and older ages (P = 0.0048) were significantly associated with worse outcomes.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study provides support for breed predispositions and identifies potential prognostic factors. Importantly, over half of the cases were considered unlikely to be vaccine-associated, demonstrating the need to investigate other underlying causes of this condition.

The role of oclacitinib in the management of ischaemic dermatopathy in four dogs

BACKGROUND

Ischaemic dermatopathy represents a heterogenous and poorly-characterized canine syndrome that is often refractory to conventional immunosuppression. Janus-kinase inhibitors (JAKinibs) are used for the treatment of various human autoimmune diseases, including dermatomyositis. Oclacitinib is a generally well-tolerated, veterinary-approved, nonselective JAKinib that has therapeutic potential as an immunosuppressant.

HYPOTHESIS/OBJECTIVES

To describe four cases of treatment refractory juvenile-onset ischaemic dermatopathy that rapidly and durably responded to oclacitinib administration.

ANIMALS

Four mixed-breed dogs, three 9-month-old male littermates and one 6-month-old female, were presented for generalized patchy alopecia, scarring and ulcerative dermatitis. Microscopic skin lesions were consistent with a severe ischaemic dermatopathy.

METHODS AND MATERIALS

A complete remission of skin lesions could not be achieved in any dog with glucocorticoids alone, nor when these were combined with adjuvant immunosuppressants. Oclacitinib treatment was then initiated at the dosage of 0.4-0.7 mg/kg twice daily, along with a tapering regimen of oral prednisolone.

RESULTS

A full clinical remission was achieved within four weeks of starting this combination therapy, with prednisolone being stopped within eight weeks thereof. Remission was maintained in two dogs with lower doses or dosing frequencies of oclacitinib, whereas the two others required persistent twice daily administration of this JAKinib.

CONCLUSIONS AND CLINICAL IMPORTANCE

Oclacitinib was a useful immunosuppressive adjuvant to oral glucocorticoids for the treatment of refractory or severe cases of ischaemic dermatopathy in these four dogs. Such observation warrants further studies of the safety, efficacy and mechanism of action of oclacitinib as an immunosuppressant.