Drug hypersensitivity reactions targeting the skin in dogs and cats

Putative pemphigus-like reaction to oral fluralaner in a dog

A 9-month-old mixed-breed dog developed generalised pustular dermatitis, accompanied by lethargy and hyperthermia, 7 days after oral fluralaner administration. Dermatopathological and microbiological evaluations were consistent with a pustular acantholytic dermatitis. A 4-month course of immunosuppressive therapy resulted in complete remission of lesions, which did not recur after therapy was withdrawn.

Fibrosis in canine transmissible venereal tumor after chemotherapy with vincristine

The canine transmissible venereal tumor is type of transmissible cancer that occurs naturally through allogenic cellular transplants. Commonly diagnosed in the genital area of sexually active dogs, the tumor typically responds well to vincristine sulfate chemotherapy, although there are cases of resistance to the drug correlated with the tumoral phenotype. We describe herein a case of fibrosis in an area affected by the tumor in a dog after vincristine chemotherapeutic treatment that was associated with an idiosyncratic reaction to the drug.

Case report: Uncommon immune-mediated skin disease involving systemic disorders in dogs

Case 1, a 6-year-old, spayed female Pug, presented with severe systemic urticaria, edema, and erythema. The dog had received a famotidine injection as a treatment for repeated vomiting in another hospital. On physical examination, hyperthermia was observed. Moderate pancytopenia, hypoalbuminemia, and increased CRP and D-dimer were also observed in blood tests. Hyposthenuric proteinuria, pulmonary interstitial infiltration, and hepatomegaly were found in other tests. In the histology of the skin, dermal edema and infiltration of inflammatory cells were observed. Therefore, she was diagnosed with acute systemic hypersensitivity. Case 2, a 13-month-old, neutered male Pembroke welsh corgi, presented with severe and patchy systemic ulcerative skin lesions. The dog had a history of soft feces and pain around the anus 2 days before. Thrombocytopenia, and increased CRP and D-dimer were observed in blood tests. In histology, epidermal necrolysis, separation of the epidermis and dermis, and infiltration of inflammatory cells were observed. Therefore, he was diagnosed with an immune-mediated disease with necrolysis dermatitis. Case 3, a 12-year-old, spayed female Pomeranian, presented with severe systemic alopecia, pustule, and crust on the skin. The dog had received an infection treatment from a local hospital. Severe regenerative anemia (hematocrit 15.3%, negative saline agglutination test, negative slide agglutination test, negative Coomb's test, prominent spherocytes) elevated liver enzymes, and increased CRP and D-dimer were observed in blood tests. On histopathology of the skin, pustules, acantholytic cells, and inflammatory cells were observed in the keratin layer of the epithelium. Therefore, she was diagnosed with Pemphigus foliaceus concurrent with immune-mediated hemolytic anemia. The 3 cases were diagnosed with fatal immune-mediated skin disease concurrently with hematological and systemic abnormalities. All the cases were treated with immune-suppressive drugs, prednisolone, and cyclosporine. In cases 2 and 3, the dogs also received human intravenous immunoglobulin as an immune modulator. The treatment was successful with significant improvements in all the 3 cases.

Recombinant human interferon-α14 for the treatment of canine allergic pruritic disease in eight dogs

BACKGROUND

Allergic pruritic diseases are increasingly common in dogs. This group of conditions hampers life quality as pruritus progressively interferes with normal behaviours. Therefore, new treatment modalities for canine allergic pruritic diseases are necessary. While novel drugs have recently reached the market, there is still the need for other therapeutic approaches. Some dogs are refractory even to the newer compounds, and cost is also an important issue for these. Older therapeutic modalities are only moderately successful or have considerable secondary effects, as is the case with glucocorticoids.

OBJECTIVES

Report on the use of recombinant human interferon-α14 (rhIFN-α14) for the treatment of canine allergic pruritus. Following the experience with a similar compound in the Japanese market, it was expected that rhIFN-α14 could alter the Th1/Th2 disbalance that drives these diseases.

METHODS

Here, we present an uncontrolled trial in which eight dogs with clinical diagnosis of allergic pruritus were treated with rhIFN-α14, either orally or via subcutaneous injections. Skin condition, microbiota and anti-interferon antibody levels were assessed.

RESULTS

The parenteral use of interferon induced hypersensitivity in two of the three dogs in which it was used. The oral administration was consistently safe and could reduce signs of the allergic condition in three of the five treated animals. Treatment also altered the skin microbiota, as verified by next-generation sequencing.

CONCLUSION

The present results indicate that rhIFN-α14 is a viable candidate for the treatment of canine allergic pruritus. Future controlled studies are needed, and the oral route is indicated for further trials.

Case Report: Positive Outcome of a Suspected Drug-Associated (Immune Mediated) Reaction in a 4-Year-Old Male French Bulldog

Toxic epidermal necrolysis (TEN) is a rare and severe life-threatening syndrome characterized by apoptosis of keratinocytes resulting in devitalization of the epidermis affecting more than 30% of skin surface. In humans and animals, this condition is mostly triggered by drugs. Identification of the putative agent and its withdrawal are crucial to successful management of a patient with TEN. In this case study, we report the clinical features, histopathological findings and management of a dog with TEN. A 4-year-old intact male French bulldog presented with acute onset of severe lethargy and cutaneous ulcerations on the footpads, scrotum, and hind limbs associated with marked pain. A Stevens-Johnson syndrome/TEN was suspected and drugs, especially beta-lactams, were withdrawn. Histopathology confirmed the diagnosis of epidermal necrosis. Advanced supportive therapy, pain management and skin care led to rapid remission. Early identification and removal of the suspected medication was crucial to improving TEN prognosis in this dog. Antibiotics (penicillin, ampicillin, cephalexin, and sulfonamides) are frequently involved in adverse cutaneous reactions in dogs. Ideal treatment remains elusive is humans and dogs and this disease has a poor prognosis. Supportive care combined with pain management and treatment of the cutaneous ulcerations is essential.

Sterile neutrophilic dermatitis in a cat associated with a topical plant-derived oil flea preventative

A 4-year-old, female spayed, domestic short hair cat presented with an acute eruption of pustules and bullous plaques after application of a plant-based, essential oil flea preventative. Histopathological evaluation of biopsies revealed severe neutrophilic infiltrate within the dermis and culture was negative. The cat's skin lesions responded rapidly to glucocorticoid monotherapy.

A retrospective study of adverse effects of mycophenolate mofetil administration to dogs with immune-mediated disease

Background

Information regarding adverse events (AEs) of mycophenolate mofetil (MMF) is limited.

Objectives

To evaluate the types and frequency of potential AEs of MMF in dogs with immune‐mediated disease.

Animals

One hundred thirty‐one dogs treated with MMF for management of suspected immune‐mediated disease.

Methods

Retrospective study. Medical records were reviewed to find and group suspect AEs in gastrointestinal (GI), hematologic, and other categories. Age, dosage, body weight, and sex were analyzed between dogs with and without AEs by using the Mann‐Whitney U‐test and chi‐squared test.

Results

The median starting dosage of MMF was 17.5 mg/kg/day (interquartile range [IQR] = 15.1‐20.6 mg/kg/day) and the median treatment duration was 56 days (IQR = 14‐236 days). Mycophenolate mofetil was prescribed for immune‐mediated hemolytic anemia (n = 31), immune‐mediated thrombocytopenia (n = 31), pemphigus foliaceus (n = 15), immune‐mediated polyarthritis (n = 12), and others (n = 42). Overall, potential AEs of MMF were observed in 34 of 131 dogs (GI 24.4% [31/127], neutropenia 4% [3/76], anemia 4% [1/25], thrombocytopenia 4.0% [1/25], and dermatologic 1.5% [2/131]). There were no significant differences among dogs with (n = 37) or without potential AEs (n = 94) in regards to sex, age, body weight, or dosage of MMF (P = .06, .13, .24, and .26, respectively).

Conclusions and Clinical Importance

In the dogs administered MMF, GI AEs were most common. Since potential hematologic and dermatologic AEs developed in a few dogs, clinicians should be aware of these when prescribing MMF to dogs with immune‐mediated disease.

Pharmacokinetics and tolerance of repeated oral administration of 5-fluorocytosine in healthy dogs

Background

5-fluorocytosine is a pyrimidine and a fluorinated cytosine analog mainly used as an antifungal agent. It is a precursor of 5-fluorouracil, which possesses anticancer properties. To reduce systemic toxicity of 5-fluorouracil during chemotherapy, 5- fluorocytosine can be used as a targeted anticancer agent. Expression of cytosine deaminase by a viral vector within a tumor allows targeted chemotherapy by converting 5-fluorocytosine into the cytotoxic chemotherapeutic agent 5-fluorouracil. However, little is known about the tolerance of 5-fluorocytosine in dogs after prolonged administration.

Results

In three healthy Beagle dogs receiving 100 mg/kg of 5-fluorocytosine twice daily for 14 days by oral route, non-compartmental pharmacokinetics revealed a terminal elimination half-life of 164.5 ± 22.5 min at day 1 and of 179.2 ± 11.5 min, after 7 days of administration. Clearance was significantly decreased between day 1 and day 7 with 0.386 ± 0.031 and 0.322 ± 0.027 ml/min/kg, respectively. Maximal plasma concentration values were below 100 µg/ml, which is considered within the therapeutic margin for human patients. 5-fluorouracil plasma concentration was below the limit of detection at all time points. The main adverse events consisted of depigmented, ulcerated, exudative, and crusty cutaneous lesions 10 to 13 days after beginning 5-fluorocytosine administration. The lesions were localized to the nasal planum, the lips, the eyelids, and the scrotum. Histological analyses were consistent with a cutaneous lupoid drug reaction. Complete healing was observed 15 to 21 days after cessation of 5-fluorocytosine. No biochemical or hematological adverse events were noticed.

Conclusions

Long term administration of 5-fluorocytosine was associated with cutaneous toxicity in healthy dogs. It suggests that pharmacotherapy should be adjusted to reduce the toxicity of 5-fluorocytosine in targeted chemotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02927-5.

Cutaneous adverse drug reaction in a dog following firocoxib treatment

A 9‐year‐old intact female toy poodle was presented with oedema around the neck, including pus and cutaneous necrosis, 2 days after starting firocoxib treatment and placement of a cervical collar for intervertebral disc disease. Cytology of the pus revealed predominantly mature neutrophils with fewer macrophages and lymphocytes, indicating sterile inflammation. Although a skin biopsy could have provided more diagnostic information, it was not performed at presentation. Firocoxib treatment was discontinued, and immunosuppressive therapy including cyclosporine was initiated, which significantly alleviated the skin lesions. The dog recovered fully in 7 weeks. The final diagnosis was a possible cutaneous adverse drug reaction to firocoxib based on history, clinical signs and response to therapy.

Model Based Evaluation of Hypersensitivity Adverse Drug Reactions to Antimicrobial Agents in Children

Drug use in children is-in most cases-supported by extrapolation of data generated from clinical trials in adult populations. This puts children at higher risk of developing adverse drug reactions (ADRs) due to "off-label" use of drugs and dosing issues. Major types of ADRs are drug hypersensitivity reactions, an idiosyncratic type of ADRs that are largely unpredictable and can cause high morbidity and mortality in a hard-to-identify specific population of patients. Lack of a complete understanding of the pathophysiology of DHRs and their unpredictive nature make them problematic in clinical practice and in drug development. In addition, ethical and legal obstacles hinder conducting large clinical trials in children, which in turn make children a "therapeutic orphan" where clear clinical guidelines are lacking, and practice is based largely on the personal experience of the clinician, hence making modeling desirable. This brief review summarizes the current knowledge of model-based evaluation of diagnosis and management of drug hypersensitivity reactions (DHRs) to antimicrobial drugs in the pediatric population. Ethical and legal aspects of drug research in children and the effect of different stages of child development and other factors on the risk of DHRs are discussed. The role of animal models, in vitro models and oral provocation test in management of DHRs are examined in the context of the current understanding of the pathophysiology of DHRs. Finally, recent changes in drug development legislations have been put forward to encourage drug developers to conduct trials in children clearly indicate the urgent need for evidence to support drug safety in children and for modeling to guide these clinical trials.

Feline pemphigus foliaceus: original case series and a comprehensive literature review

BACKGROUND

Since the first description of feline pemphigus foliaceus (PF) more than 30 years ago, numerous case reports have been published, while larger case series have remained rare. This large body of information, if extrapolated, could address clinical discrepancies and expand our knowledge about the treatment of feline PF. This manuscript reviews cases of feline PF published between 1950 and 2016 and adds additional 35 original cases to provide further insight into the clinical aspect and treatment outcome of this disease.

RESULTS

Feline PF, while being a primary acantholytic pustular dermatosis, presents most often with crusts and erosions that predominantly affect the face and feet. More than half of cats with active disease exhibits non-dermatological signs such as lethargy, fever and/or anorexia. The prognosis of feline PF is good as the majority of cats rapidly achieve disease control even with the most basic treatment such as glucocorticoid monotherapy. Most PF-affected cats, however, require long-term treatment and, like other autoimmune diseases, feline PF has a tendency to relapse spontaneously or with treatment changes.

CONCLUSIONS

Therefore, despite the overall good prognosis cats with PF can be given, owners should be informed and prepared for these circumstances, which may reduce the risk of euthanasia in the case of disease relapse, and improve treatment compliance.

Probable cutaneous adverse drug reaction to piroxicam in a cat

Case summary

A 9-year-old male neutered Devon Rex cat presented with bilaterally symmetrical ulcerative lesions with mucopurulent exudate that developed rapidly. The lesions were apparent on the axillae, ventral abdomen and inguinal areas. The cat was systemically well. Piroxicam was being administered for palliative treatment of a previously diagnosed salivary adenocarcinoma. Histopathology revealed severe extensive epidermal ulceration with focal dyskeratotic keratinocytes in the stratum granulosum without lymphocyte satellitosis. Resolution of skin lesions was observed after discontinuing piroxicam. Similar lesions developed after previous piroxicam administration, further suggesting a possible adverse reaction to this drug. In addition, the Naranjo score indicated that piroxicam was a probable cause for the ulcerative skin lesions.

Relevance and novel information

This is the first report of piroxicam, a non-steroidal anti-inflammatory drug, as a probable cause of ulcerative skin lesions in a cat.

In Vitro Research Tools in the Field of Human Immediate Drug Hypersensitivity and Their Present Use in Small Animal Veterinary Medicine

Drug hypersensitivity reactions (DHR) are immune-mediated idiosyncratic adverse drug events. Type I DHR are often referred to as "immediate" and involve B lymphocyte-secreted IgE that bind to the membrane of basophils and mast cells, inducing their degranulation. This review presents various in vitro tests that were developed in the field of human type I HS and implemented as clinical diagnostic tools in human cases of immediate DHR. The respective strengths and weaknesses of each test will be discussed in parallel of validation data such as specificity and sensitivity whenever available. Some of them have also been used as diagnostic tools in veterinary medicine, but not in cases of immediate DHR. Most of these diagnostic tools can be categorized into humoral and cellular tests. The former tests measure serum concentrations of factors, such as histamine, tryptase, and drug-specific IgE. The latter assays quantify markers of drug-induced basophil activation or drug-specific lymphocyte proliferation. Pharmacogenetic markers have also been investigated in immediate DHR, but not as extensively as in non-immediate ones. Throughout, practical aspects and limitations of the tests, as well as sensitivity and specificity parameters, will be presented. In addition, the experience of veterinary medicine with these diagnostic tools will be summarized. However, to date, none of them has ever been reported in a veterinary case of type I DHR.

Pyoderma gangrenosum after trauma in a dog

A 12-year-old male entire Miniature Pinscher presented with excoriations at various body sites, progressively forming ulcers and enlarging until arrested by treatment. Based on the clinical presentation and histopathological analyses, sterile neutrophilic dermatosis was suspected. Therefore, the dog was started on prednisolone. Marked improvement was achieved with prednisolone treatment, suggesting a diagnosis of pyoderma gangrenosum (PG). Transcription levels of cytokine mRNA in lesional skin before and after treatment from this dog were quantified by real-time RT-PCR. Transcription levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-8 and IL-17A were higher in lesional skin before treatment than after treatment. Levels of various cytokines could be increased in lesional skin of dogs with PG as well as in human patients with PG.

Cutaneous Adverse Drug Reactions in Dogs Treated with Antiepileptic Drugs

Epilepsy is one of the most common neurologic disorders in dogs and life-long treatment with antiepileptic drugs (AED) is frequently required. Adverse events of AED targeting the skin are only rarely reported in veterinary medicine and the true incidence and spectrum of cutaneous reactions in epileptic dogs remains unknown. In this study, we hypothesized that cutaneous reactions commonly occur in epileptic dogs and are related to AED treatment. A retrospective case review of 185 dogs treated for epilepsy identified 20.0% with simultaneous appearance of dermatologic signs. In a subsequent prospective case investigation (n = 137), we identified newly appearing or distinct worsening of skin lesions following initiation of AED therapy in 10.9% of dogs treated for epilepsy (95% CI 6.8–17.7%). Cutaneous lesions were classified as probably drug-induced in 40.0% of these cases. Patch testing and intradermal testing were further investigated as potential diagnostic methods to confirm AED hypersensitivity. They were of high specificity but sensitivity and positive predictive value appeared inappropriate to recommend their routine use in clinical practice.

Cutaneous adverse drug reaction in a dog associated with imepitoin

BACKGROUND

The macroscopic appearance of cutaneous adverse drug reactions can be similar to a plethora of skin diseases and in particular may resemble autoimmune and immune-mediated disorders. The reaction can occur after single or multiple administrations, with the latter varying in durations of up to years of treatment. These reactions are mostly self-limiting with cessation of the offending drug.

OBJECTIVES

To report a cutaneous adverse drug reaction associated with chronic administration of imepitoin.

CASE REPORT

A 4-year-old, Jack Russell terrier dog was presented with progressive skin lesions of 1-week duration. The dog had a 6 month history of idiopathic epilepsy treated with imepitoin for the previous 5 months. Imepitoin is an anti-epileptic drug that acts as a low-affinity partial agonist of the benzodiazepine site at the GABAA receptor. The dosage of imepitoin was increased from 20 mg/kg twice daily to 30 mg/kg twice daily, 3 days before the onset of skin lesions, due to uncontrolled seizures. [Correction added on 15 February 2016 after first online publication: In the preceding sentence, the dosage of imepitoin was previously incorrect and has been amended in this current version.] Dermatological examination revealed erythema and exfoliation at the mucocutaneous junctions of the lips, lip folds, philtrum, ears, axillae and the ventral abdomen. Small erosions and depigmentation were visible on the oral mucosa, lip folds and philtrum. Histopathology was supportive of a lupoid drug reaction. Complete resolution of skin lesions was seen after discontinuation of imepitoin and low dose of prednisolone during a period of 4 weeks. No recrudescence of skin lesions was observed during a 6 month follow-up period.

CONCLUSION AND CLINICAL IMPORTANCE

Imepitoin may result in cutaneous adverse drug reactions in dogs.

Potential cutaneous hypersensitivity reaction to an inactive ingredient of thyroid hormone supplements in a dog

BACKGROUND

Although discussions about allergic reactions to thyroid supplements abound on professional forums, there is almost no information in the literature on these specific idiosyncratic drug reactions.

ANIMAL

A dog with a history of hypothyroidism-associated weight gain and mild lethargy was prescribed levothyroxine tablets (0.018 mg/kg twice daily). After 19 days the dog developed a severe skin condition that was responsive to levothyroxine withdrawal, and antibiotic and glucocorticoid therapy. Three weeks later a different levothyroxine tablet was prescribed. Within 48 h the dog developed a more severe cutaneous reaction that resolved with drug discontinuation and appropriate topical care.

OBJECTIVES

To confirm a possible hypersensitivity reaction and identify its chemical target.

METHODS AND RESULTS

The two prescribed levothyroxine formulations shared two inactive ingredients: magnesium stearate and polyvinylpyrrolidone. Nine months after discontinuation of thyroid supplement, a formulation without either of these two compounds was used for a second re-challenge. There was no recurrence of the drug reaction and after 1.5 years of treatment the dog remains normal.

CONCLUSIONS AND CLINICAL IMPORTANCE

These elements strongly suggest that this dog had an idiosyncratic reaction (likely immune-mediated) against one or both inactive ingredients in the first two formulations of levothyroxine. We are not aware of any previous confirmed delayed hypersensitivity to a thyroid supplement in a dog with the likely chemical trigger being an inactive ingredient rather than the therapeutic agent itself. We hope that this case will raise awareness about allergic reactions to thyroid supplements and allergic reactions to inactive formulation components.

Erythema multiforme associated with zonisamide in a dog

This report describes a dog that developed erythema multiforme in temporal association with administration of the sulphonamide-based anticonvulsant drug zonisamide. Similar adverse drug reactions have been associated with sulphonamide antimicrobial drugs. Caution should be exercised when prescribing this medication for dogs with known hypersensitivity to sulphonamides.

Erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis: a comparative review

BACKGROUND

Human erythema multiforme (EM) and Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) are separate conditions. There is no consensus on classification criteria for the eponymous diseases in animals.

RESULTS

Animal EM is very different from 90% of human EM, which is herpes virus associated (HAEM). Animals lack acrally distributed, typical raised targets. Unlike canine parvovirus 'EM', HAEM is not an active infection. Animal EM is often attributed to drugs, but this is rarely proved. Conversely, human and animal SJS/TEN are almost identical, life-threatening disorders of epidermal necrosis and detachment, typically triggered by drugs (occasionally by infectious agents). Both EM and SJS/TEN are mediated by cytotoxic lymphocyte responses against altered keratinocytes (infectious agents or drugs). Apoptosis results from direct cytotoxicity or through soluble mediators, namely Fas ligand, granzymes, perforin and granulysin. Diagnosis in humans is clinicopathological, with emphasis on clinical lesions; histopathology confirms the pathological process as interface (cytotoxic) dermatitis. Human EM is self-limiting; only recurrent and rare persistent cases require antiviral/immunosuppressive therapies. Drug-induced EM responds to drug withdrawal. Idiopathic canine EM (>40%) is usually chronic, refractory to treatment and may represent heterogeneous conditions. Early identification and removal of the causative drug and high-quality supportive care are critical in SJS/TEN. Mortality rate is nevertheless high.

CONCLUSIONS AND CLINICAL IMPORTANCE

(1) Histopathological lesions do not reliably differentiate EM, SJS and TEN. (2) A multicentre study to develop a consensus set of clinical criteria for EM and SJS/TEN in animals is overdue. (3) No adjunctive therapies, including intravenous immunoglobulin and ciclosporin, have met evidence-based standards.

Clinical and Microscopic Characteristics of Canine Toxic Epidermal Necrolysis

Canine toxic epidermal necrosis (TEN), a rare and life-threatening cutaneous drug reaction, traditionally has been described as full-thickness devitalization of the epidermis with minimal dermal inflammation; however, few reports detail the histologic findings. We characterize the clinical features and histologic variations of 3 canine TEN patients. Clinically, irregular erythematous and purpuric macules evolved into widespread and severely painful erosions. The number of eroded mucosae varied; however, periocular and perilabial mucocutaneous junctions frequently were affected. Thirteen of 17 biopsies were evaluated. Apoptosis at multiple epidermal levels was the most common pattern of epidermal necrosis (12/13 biopsies, 92%). In contrast, full-thickness coagulation necrosis was present less often (7/13 biopsies, 52%). Lymphocytic interface dermatitis was the predominant inflammatory pattern, and intraepidermal lymphocytes, along with fewer histiocytes, were present to some degree in all samples along with lymphocytic satellitosis of apoptotic keratinocytes. The sequence of changes points to lymphocyte-mediated keratinocyte apoptosis as an early step in lesion development with subsequent variation in progression to coagulation necrosis among patients. Histopathologic changes overlapped with those reported for erythema multiforme, in contrast to traditional histologic descriptions of canine TEN. A specific algorithm for assessment of drug causality in epidermal necrolysis (ALDEN) was applied for each patient; carprofen was associated with a probable score for causality in 1 dog. Clinicians should be encouraged to take multiple biopsies in TEN suspect cases as nearly 25% of all biopsies lacked epithelium and were not diagnostic.

The effect of 'allergenic' and 'nonallergenic' antibiotics on dog keratinocyte viability in vitro

BACKGROUND

Immune-mediated adverse drug reactions (drug hypersensitivity) are relatively common in veterinary medicine, but their pathogenesis is not well understood. For an unknown reason, delayed drug hypersensitivity often targets the skin. Antibiotics, especially β-lactams and sulfonamides, are commonly associated with these adverse events. The 'danger theory' hypothesizes that 'danger' signals, such as drug-induced cell death, might be part of the pathogenesis of drug hypersensitivity reactions.

HYPOTHESIS/OBJECTIVES

The goal of this study was to determine whether antibiotics that are commonly associated with cutaneous drug hypersensitivity (allergenic) decrease canine keratinocyte viability in vitro more than antibiotics that rarely cause such reactions (nonallergenic).

METHODS

Immortalized canine keratinocytes (CPEK cells) were exposed to a therapeutic range of drug concentrations of four 'allergenic' antibiotics (two β-lactams, i.e. amoxicillin and cefalexin, and two sulfonamides, i.e. sulfamethoxazole and sulfadimethoxine) or two 'nonallergenic' antibiotics (enrofloxacin and amikacin) over 48 h (2, 4, 8, 24 and 48 h). The reactive nitroso metabolite of sulfamethoxazole was also tested.

RESULTS

Cefalexin (2 mmol/L) significantly decreased cell viability after 48 h (28 ± 7%; P = 0.035). The nitroso metabolite of sulfamethoxazole (100 μmol/L) decreased cell viability after 2 h (21 ± 7%; P = 0.049), but cell numbers were increased after 8 h (22 ± 6%; P = 0.018). In addition, enrofloxacin (500 μmol/L) also significantly decreased cell viability by 37% (±6%; P = 0.0035) at 24 h and by 70% (±8%; P < 0.001) at 48 h.

CONCLUSION

It appears that the effect of drugs on the in vitro viability of dog keratinocytes is not a good predictor of the 'allergenic' potential of an antibiotic. Further work is required to investigate other drug-induced 'danger' signals in dog keratinocytes exposed to 'allergenic' antibiotics in vitro.

Cutaneous vasculitis in small animals

Cutaneous vasculitis is an inflammatory process targeting blood vessels. Underlying factors include drugs, infectious diseases, adverse reactions to food, malignancies, and immune-mediated diseases. Vasculitis is a reaction pattern warranting a workup to identify triggers. Presenting symptoms include purpura, pitting edema, and skin ulcerations. Constitutional signs include fever, depression, and anorexia and seem to be present in the majority of patients. Once a diagnosis is confirmed, treatment and follow-up must be tailored to the individual. High-dose immunosuppressive medications are only recommended once infectious diseases capable of producing a similar constellation of clinical signs have been ruled out.