Incidence, timing, and risk factors of azathioprine hepatotoxicosis in dogs

Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is an underrecognized cause of hepatic disease in dogs and cats. Successful identification of cases requires an initial suspicion by the practitioner, a thorough drug exposure history, and knowledge of the toxic potential for common veterinary drugs. This article reviews the pathogenesis, classification, and diagnosis of DILI in small animals. It also discusses the clinical presentation, prevalence, and outcomes of DILI for several drugs important in veterinary medicine including azathioprine, azole antifungals, carprofen, diazepam, doxycycline, lomustine, methimazole, phenobarbital, rifampin, sulfonamide antibiotics, and zonisamide, as well as the toxic potential for nutraceuticals and herbal preparations.

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.

Antiviral Potential of Azathioprine and Its Derivative 6- Mercaptopurine: A Narrative Literature Review

The use of azathioprine (AZA) in human medicine dates back to research conducted in 1975 that led to the development of several drugs, including 6-mercaptopurine. In 1958, it was shown that 6-mercaptopurine decreased the production of antibodies against earlier administered antigens, raising the hypothesis of an immunomodulatory effect. AZA is a prodrug that belongs to the thiopurine group of drugs that behave as purine analogs. After absorption, it is converted into 6-mercaptopurine. Subsequently, it can be degraded through various enzymatic pathways into inactive compounds and biologically active compounds related to the mechanism of action, which has been the subject of study to evaluate a possible antiviral effect. This study aims to examine the metabolism, mechanism of action, and antiviral potential of AZA and its derivatives, exploring AZA impact on antiviral targets and adverse effects through a narrative literature review. Ultimately, the review will provide insights into the antiviral mechanism, present evidence of its in vitro effectiveness against various DNA and RNA viruses, and suggest in vivo studies to further demonstrate its antiviral effects.

The use of oclacitinib compared to azathioprine in the management of canine pemphigus foliaceus: A retrospective analysis

BACKGROUND

Oclacitinib (Apoquel; Zoetis) has been reported to be beneficial for treating immune-mediated disorders.

HYPOTHESIS/OBJECTIVES

This retrospective study evaluates in which group of dogs [oclacitinib (OC) or azathioprine (AZ)] remission of pemphigus foliaceus (PF) was more effectively achieved with matched induction dosing of glucocorticoids; it further evaluates which group had a higher glucocorticoid-sparing effect.

ANIMALS

Review of 30 medical records of dogs diagnosed with PF presented to a private practice dermatological service.

MATERIALS AND METHODS

Retrospective analysis of dogs diagnosed with PF and treated with OC or AZ in combination with glucocorticoids.

RESULTS

There was no significant difference in the ability to induce remission between AZ and OC groups. In the AZ group, 13 of 15 dogs went into some type of remission (partial or complete), compared with 11 of 15 in the OC group. There was no significant difference between the two groups for the glucocorticoid-sparing effect. The AZ group had an average reduction of 77.9% from the induction glucocorticoid dose, and OC group had an average reduction of 64.4%. One of 15 patients in the AZ group and three of 15 patients in the OC group had a 100% reduction of the glucocorticoid dose.

CONCLUSIONS AND CLINICAL RELEVANCE

These results indicate that OC can be considered as a treatment option for canine PF.

Mycophenolate mofetil as a treatment for presumed idiopathic chronic hepatitis in dogs: Six cases (2010-2022)

OBJECTIVES

The objectives of this study were to describe the clinical findings, treatment and outcomes of six dogs with presumed idiopathic chronic hepatitis treated with mycophenolate mofetil (MMF).

MATERIALS AND METHODS

Medical records were retrospectively searched to identify dogs in which idiopathic chronic hepatitis was diagnosed on histopathology between January 2010 and June 2022 that were treated with MMF for at least two weeks with >2 follow-up examinations. Data recorded from each dog included signalment, clinical signs, diagnostic test results and treatment.

RESULTS

Six dogs were treated with MMF at a median initial dosage of 9.6 mg/kg PO q 12 h. Reported adverse effects from MMF included decreased appetite, vomiting and diarrhoea. In all six dogs, MMF was used successfully long term for the treatment of idiopathic chronic hepatitis as determined by 46% or greater improvement of alanine aminotransferase (ALT) between 4 and 18 weeks of starting MMF. Three dogs were also temporarily treated for 4-6 months on a tapering dose of prednisone. In two dogs, ALT remained within the reference interval, and in one dog, it was very mildly elevated when on MMF alone. In all six dogs, owners reported that the medication was well tolerated.

CLINICAL SIGNIFICANCE

To the authors' knowledge, this is the first report describing the use of MMF with and without a tapering dose of prednisone for the treatment of idiopathic chronic hepatitis in six dogs. Based on the outcomes of the dogs in this report, MMF can be effective for the long-term treatment of idiopathic chronic hepatitis as measured by reduction in ALT and improvement of clinical signs.

A shortened whole brain radiation therapy protocol for meningoencephalitis of unknown origin in dogs

Introduction

A variety of treatment options have been described for canine meningoencephalitis of unknown origin (MUO). Few studies focused on radiation therapy as a second line immunomodulating treatment, implicating its effective use. However, a standard radiation therapy protocol is lacking, and further research will help to evaluate the effect of different dose regimens.

Methods

Ten dogs diagnosed with MUO based on MRI and CSF findings were prospectively enrolled. The dogs were treated with a shortened whole brain radiation therapy protocol (5 × 4 Gy) in combination with prednisolone. Neurologic changes were quantified using an established scoring scheme. Follow-up MRI and CSF examination was scheduled three months after radiation therapy. Overall survival and time to progression were calculated. Histopathology of the brain was performed in case of death.

Results

Seven dogs were diagnosed de novo and three had a history of relapsing MUO. Neurological status improved in all 10 dogs during radiation therapy, with 4/10 returning to normal shortly after radiation therapy. Three dogs died within the first three months after radiation therapy. At follow-up MRI lesions completely resolved in two dogs, partially resolved in five dogs, and progressed in one dog. After follow-up MRI, dogs were further treated with prednisolone monotherapy (two dogs) and additional immunosuppressant drugs (five dogs). Overall, four dogs showed disease progression, with a mean time to progression of 691 days (95%CI: 396-987) and mean overall survival for all dogs was 723 days (95%CI: 436-1011) (both medians not reached). Histopathology confirmed MUO in three dogs but was suggestive for oligodendroglioma in one dog. Radiation induced side effects were not seen.

Conclusion

Shortened whole-brain radiation therapy could be an additional treatment option for MUO in conjunction to prednisolone, specifically for cases that require rapid relief of symptoms and with relapsing history.

Prevalence of hepatotoxicity and myelosuppression with alternate day use of azathioprine and glucocorticoids for treatment of dermatological conditions in dogs

BACKGROUND

The use of azathioprine (AZA) in dogs is limited by the potential for hepatotoxicity and myelosuppression.

HYPOTHESIS/OBJECTIVES

To determine the prevalence of AZA-associated hepatotoxicity in dogs with dermatological conditions receiving alternate-day AZA. The hypothesis was that dogs receiving AZA every other day (EOD) would have a lower prevalence of hepatotoxicity compared to published data for dogs receiving daily AZA. A secondary aim was to determine the prevalence of AZA-associated myelosuppression over the same time period and population.

ANIMALS

Forty-one client-owned dogs with dermatological conditions treated with AZA EOD and glucocorticoids with clinical and haematological follow-up available for a minimum of two months of AZA therapy.

METHODS

Retrospective analysis of data from April 1994 to July 2020. Hepatotoxicity was defined as elevation of alanine aminotransferase (ALT) at least twofold above the reference range.

RESULTS

Azathioprine-associated hepatotoxicity was observed in two of 41 dogs (4.9%), with onset at 18 and 40 days, respectively. One dog receiving AZA at 1.9 mg/kg EOD had a fourfold increase in ALT. The other dog (AZA dose 2.3 mg/kg EOD) had a 30-fold increase in ALT. Azathioprine was not associated with thrombocytopenia, anaemia or neutropenia in any dogs. Lymphopenia developed in one dog (2.4%) with onset at 105 days.

CONCLUSIONS AND CLINICAL RELEVANCE

Alternate-day AZA administration with tapering glucocorticoids was well-tolerated in dogs with dermatological conditions.

Combination of Prednisolone and Azathioprine for Steroid-Responsive Meningitis-Arteritis Treatment in Dogs

Treatment with high corticosteroid dosages for steroid-responsive meningitis-arteritis (SRMA) is correlated with severe adverse effects and worse quality of life. In order to improve immunosuppression and decrease dosage and duration of glucocorticoid treatment, a second immunosuppressive drug is commonly used in most of the immune-mediated diseases. The objective of this retrospective study was to evaluate the efficacy, tolerability, and occurrence of relapse for the combination of prednisolone and azathioprine. All dogs received azathioprine 2 mg/kg q 24 hr for 1 mo and then 2 mg/kg every other day for 2 mo; prednisolone was started at an immunosuppressive dosage and tapered off gradually during a mean of 3 mo. Twenty-six dogs met inclusion criteria. Twenty-one dogs (81%) were in clinical remission with no relapse observed within the 2 yr follow-up period. Treatment was well tolerated in all dogs and side effects were most of the time mild and self-limiting. The relapse rate (19%) was lower than most published rates. A prednisolone and azathioprine combination appeared to be effective for primary treatment of dogs with SRMA and allows a quicker tapering in prednisolone dosage, a decrease in long-term side effects of steroids, a shorter duration of treatment, and a low relapse rate.

ACVIM consensus statement on the treatment of immune-mediated hemolytic anemia in dogs

Immune‐mediated hemolytic anemia (IMHA) causes severe anemia in dogs and is associated with considerable morbidity and mortality. Treatment with various immunosuppressive and antithrombotic drugs has been described anecdotally and in previous studies, but little consensus exists among veterinarians as to the optimal regimen to employ and maintain after diagnosis of the disease. To address this inconsistency and provide evidence‐based guidelines for treatment of IMHA in dogs, we identified and extracted data from studies published in the veterinary literature. We developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria, explanation of treatment regimens, and validity of statistical methods. In combination with our clinical experience and comparable guidelines for humans afflicted with autoimmune hemolytic anemia, we used the conclusions of this process to make a set of clinical recommendations regarding treatment of IMHA in dogs, which we refined subsequently by conducting several iterations of Delphi review. Additionally, we considered emerging treatments for IMHA in dogs and highlighted areas deserving of future research. Comments were solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted for publication. The resulting document is intended to provide clinical guidelines for management of IMHA in dogs. These guidelines should be implemented pragmatically, with consideration of animal, owner, and veterinary factors that may vary among cases.

Development and implementation of a novel immune thrombocytopenia bleeding score for dogs

Background

A method of quantifying clinical bleeding in dogs with immune thrombocytopenia (ITP) is needed because ITP patients have variable bleeding tendencies that inconsistently correlate with platelet count. A scoring system will facilitate patient comparisons and allow stratification based on bleeding severity in clinical trials.

Hypothesis/Objectives

To develop and evaluate a bleeding assessment tool for dogs, and a training course for improving its consistent implementation.

Animals

Client‐owned dogs (n = 61) with platelet counts <50,000/μL; 34 classified as primary ITP, 17 as secondary ITP, and 10 as non‐ITP.

Methods

A novel bleeding assessment tool, DOGiBAT, comprising bleeding grades from 0 (none) to 2 (severe) at 9 anatomic sites, was developed. Clinicians and technicians completed a training course and quiz before scoring thrombocytopenic patients. The training course was assessed by randomizing student volunteers to take the quiz with or without prior training. A logistic regression model assessed the association between training and quiz performance. The correlation of DOGiBAT score with platelet count and outcome measures was assessed in the thrombocytopenic dogs.

Results

Clinicians and technicians consistently applied the DOGiBAT, correctly scoring all quiz cases. The odds of trained students answering correctly were higher than those of untrained students (P < .0001). In clinical cases, DOGiBAT score and platelet count were inversely correlated (r_s = −0.527, P < .0001), and DOGiBAT directly correlated with transfusion requirements (r_s = 0.512, P < .0001) and hospitalization duration (r_s = 0.35, P = .006).

Conclusions and Clinical Importance

The DOGiBAT and assessment quiz are simple tools to standardize evaluation of bleeding severity. With further validation, the DOGiBAT may provide a clinically relevant metric to characterize ITP severity and monitor response in treatment trials.

Rifampicin treatment of canine pyoderma due to multidrug-resistant meticillin-resistant staphylococci: a retrospective study of 32 cases

BACKGROUND

Rifampicin has received increased interest in veterinary dermatology because of its activity against multidrug-resistant meticillin-resistant staphylococci (MRS). There is limited knowledge about the efficacy and safety of rifampicin in dogs.

HYPOTHESIS/OBJECTIVE

To provide information on response to treatment and adverse effects in dogs treated with rifampicin for multidrug-resistant MRS pyoderma.

ANIMALS

Thirty two dogs treated with rifampicin for rifampicin-susceptible multidrug-resistant MRS pyoderma.

METHODS

Retrospective review of medical records, including alanine aminotransferase (ALT) and alkaline phosphatase (ALP) serum activity levels and total bilirubin concentrations, obtained before and throughout the treatment, was performed.

RESULTS

Oral rifampicin as sole systemic antimicrobial therapy (median dose 5 mg/kg twice daily) was effective in 71.88% of cases. Topical antimicrobials were used in most cases. Median duration of rifampicin treatment was five weeks for superficial pyoderma and four weeks for deep pyoderma. Gastrointestinal signs were reported in 15% of treated dogs. Statistically significant increases of ALT (P = 0.045) and ALP (P = 0.0002) values after 3-4 weeks of treatment was observed. The median increase was equal to 0.3 and ×1.5 the upper limit of the reference ranges for ALT and ALP, respectively.

CONCLUSIONS/CLINICAL IMPORTANCE

Oral rifampicin combined with topical antimicrobials can be considered an effective therapeutic option for canine superficial and deep pyoderma caused by rifampicin-susceptible multidrug-resistant MRS. Liver enzyme induction might be the most important cause of ALT and ALP increase associated with rifampicin therapy in dogs.

Canine autoimmune hemolytic anemia: management challenges

Immune-mediated hemolytic anemia is one of the most common manifestations of canine immune-mediated disease, yet treatment regimens remain nonstandardized and, in some cases, controversial. The main reason for this, as for most diseases in veterinary medicine, is the lack of large-scale placebo-controlled trials so that the efficacy of one treatment over another can be established. Most of the evidence used for treatment comes from retrospective studies and from personal preference and experience, and because of this, treatment regimens tend to vary among institutions and individual clinicians. Management of immune-mediated hemolytic anemia includes immunosuppression, thromboprophylaxis, and supportive care measures to help prevent and treat concurrent conditions.

Effects of azathioprine, 6-mercaptopurine, and 6-thioguanine on canine primary hepatocytes

OBJECTIVE

To investigate the cytotoxic effects of azathioprine, 6-mercaptopurine, and 6-thioguanine on canine hepatocytes.

SAMPLE

Commercially available cryopreserved canine primary hepatocytes.

PROCEDURES

The study consisted of 2 trials. In trial 1, hepatocytes were incubated with azathioprine, 6-mercaptopurine, or 6-thioguanine at 1 of 6 concentrations (0.468, 0.937, 1.875, 3.750, 7.500, or 15.000 μmol/L) for 24, 48, or 72 hours. At each time, cell viability and lactate dehydrogenase (LDH) activity were determined for each thiopurine-concentration combination, and alanine aminotransferase (ALT) activity was determined for cells incubated with each thiopurine at a concentration of 15 μmol/L. In trial 2, hepatocytes were incubated with azathioprine, 6-mercaptopurine, or 6-thioguanine at 1 of 3 concentrations (18.75, 37.50, or 75.00 μmol/L) for 24 hours, after which the free glutathione concentration was determined for each thiopurine-concentration combination and compared with that for hepatocytes incubated without a thiopurine (control).

RESULTS

Incubation of hepatocytes with each of the 3 thiopurines adversely affected cell viability in a time- and concentration-dependent manner; however, this decrease in cell viability was not accompanied by a concurrent increase in LDH or ALT activity. Likewise, free glutathione concentration for hepatocytes incubated for 24 hours with supratherapeutic thiopurine concentrations (> 18.75 μmol/L) did not differ significantly from that of control cells.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that thiopurines adversely affected the viability of canine hepatocytes in a time- and concentration-dependent manner but had a nonsignificant effect on the LDH and ALT activities and free glutathione depletion of those hepatocytes.