Leflunomide pharmacokinetics after single oral administration to dogs

Leflunomide for the Treatment of Immune-Mediated Uveitis in a Dog

A 5 yr old castrated male bichon frise presented with chronic bilateral uveitis that had previously been controlled with systemic steroid administration for 6 mo, resulting in weight gain, polyuria, and polydipsia. To control the uveitis without systemic side effects, oral cyclosporine was started after discontinuing oral steroid, but discontinued one month later because of severe vomiting. Leflunomide (2 mg/kg q 12 hr) was initiated, and the uveitis symptoms resolved after 2 mo. The dose was tapered according to the remission of clinical signs, with no relapse during the following 13 mo. Leflunomide therapy was then discontinued due to vomiting caused by severe gastroenteritis and pancreatitis, and topical prednisolone monotherapy was continued . At 8 mo after discontinuation of leflunomide, bilateral uveitis recurred, and leflunomide therapy was resumed. However, the patient lost vision due to the progression of clinical signs at 33 mo after commencing leflunomide, and evisceration of the glaucomatous right eye was performed at 43 mo. Histopathologic examination revealed lymphocyte and plasma cell infiltration and melanin-laden macrophages in the uveal tissue, and the patient was diagnosed with immune-mediated uveitis. This case indicated that oral leflunomide may be a viable treatment option for canine idiopathic immune-mediated uveitis.

Retrospective evaluation of prognosis and survival with various immunosuppressants in 82 dogs diagnosed with meningoencephalitis of unknown etiology (2010-2021)

BACKGROUND

Meningoencephalomyelitis of unknown etiology (MUE) is a comprehensive term for non-infectious inflammatory brain diseases of the central nervous system (CNS) caused by abnormal autoimmune responses. This study aims to compare the differences in survival and clinical response of MUE according to the adjuvant immunosuppressant use. Medical records of 82 dogs diagnosed with MUE were reviewed retrospectively.

RESULTS

The overall survival time was 769 days (range 14-2687 days). The median survival time for each adjunctive was: leflunomide 1035 days (range 126-2163 days), mycophenolate mofetil 865 days (range 39-2191 days), cyclosporin 441 days (range 11-2176 days), cytosine arabinoside 754 days (range 6-1898 days) and a combination of mycophenolate mofetil and cytosine arabinoside 132 days (range 23-1227 days). There was no significant difference in the incidence rate of adverse events according to the immunosuppressants, but moderate to severe anemia was confirmed in 3 patients (18.7%) in the leflunomide group.

CONCLUSIONS

The survival time and response rate of MUE dogs differed depending on which adjunctive immunosuppressants were used. Leflunomide showed a long survival time and a relatively good response rate in dogs with MUE. However, a large-scale further study with standardized doses of immunosuppressants and supportive treatment and constant monitoring interval is needed.

Inhibition of canine distemper virus replication by blocking pyrimidine nucleotide synthesis with A77 1726, the active metabolite of the anti-inflammatory drug leflunomide

Canine distemper virus (CDV) is the aetiological agent that causes canine distemper (CD). Currently, no antiviral drugs have been approved for CD treatment. A77 1726 is the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide. It inhibits the activity of Janus kinases (JAKs) and dihydroorotate dehydrogenase (DHO-DHase), a rate-limiting enzyme in de novo pyrimidine nucleotide synthesis. A77 1726 also inhibits the activity of p70 S6 kinase (S6K1), a serine/threonine kinase that phosphorylates and activates carbamoyl-phosphate synthetase (CAD), a second rate-limiting enzyme in the de novo pathway of pyrimidine nucleotide synthesis. Our present study focuses on the ability of A77 1726 to inhibit CDV replication and its underlying mechanisms. Here we report that A77 1726 decreased the levels of the N and M proteins of CDV and lowered the virus titres in the conditioned media of CDV-infected Vero cells. CDV replication was not inhibited by Ruxolitinib (Rux), a JAK-specific inhibitor, but by brequinar sodium (BQR), a DHO-DHase-specific inhibitor, and PF-4708671, an S6K1-specific inhibitor. Addition of exogenous uridine, which restores intracellular pyrimidine nucleotide levels, blocked the antiviral activity of A77 1726, BQR and PF-4708671. A77 1726 and PF-4708671 inhibited the activity of S6K1 in CDV-infected Vero cells, as evidenced by the decreased levels of CAD and S6 phosphorylation. S6K1 knockdown suppressed CDV replication and enhanced the antiviral activity of A77 1726. These observations collectively suggest that the antiviral activity of A77 1726 against CDV is mediated by targeting pyrimidine nucleotide synthesis via inhibiting DHO-DHase activity and S6K1-mediated CAD activation.

Teriflunomide inhibits activation-induced CD25 expression on T cells and may affect Foxp3-expressing regulatory T cells

Teriflunomide (TER) is an immunomodulatory agent. Although the first reports on the use of TER in dogs have already appeared, immune mechanisms underlying the immunomodulatory effect of TER do not seem to have been fully elucidated yet. There were two aspects of this study. First, further insight into the mode of action of TER was gained by investigating its effect on the expression of IL-2 receptor α-chain (CD25) and Forkhead box P3 (Foxp3) by CD4⁺ and CD8⁺ T cells and apoptosis of these cells. Second, in view in the earlier lack of data on the effect of TER on T cells in dogs, the results of this study filled in this gap. TER at a concentration which can be achieved in vivo prevented or reduced the activation-induced CD25 expression on CD4⁺ and CD8⁺ T cells, respectively. Taking into consideration the role of CD25 in T cell proliferation, this effect may constitute an additional mechanism responsible for the antiproliferative effect of the drug. Under stimulation conditions, TER induced Foxp3 expression in Foxp3-negative CD4⁺ and CD8⁺ T cells, while down-regulating it under unstimulated conditions. These results suggest that TER may generate iTreg cells, but this process requires cell activation. TER was not found to affect on the absolute count and apoptosis of CD4⁺ and CD8⁺ T cells. The results suggest that the impairment of CD25 expression during T cell activation and generation of iTreg cells may constitute additional mechanisms, besides the principal one, underlying the immunomodulatory effect of TER.

A Retrospective Study on the Safety and Efficacy of Leflunomide in Dogs

Background

Little clinical information is available concerning the use of leflunomide in dogs with immune‐mediated diseases.

Objectives

To report the safety and efficacy of leflunomide for the treatment of naturally occurring immune‐mediated diseases in dogs.

Animals

Ninety‐two dogs treated with leflunomide for management of suspected immune‐mediated diseases.

Methods

Retrospective medical record review from Jan 1995 to Dec 2014. Data that were extracted from the medical records included signalment, body weight, underlying indication for leflunomide, dosage of leflunomide, treatment duration, concurrent medications, treatment response, and adverse events.

Results

Adverse events that could be related to leflunomide administration included diarrhea (3 of 92, 3.3%), lethargy (2 of 92, 2.2%), unexplained hemorrhage (3 of 92, 3.3%), thrombocytopenia (2 of 31, 6.5%), and increased liver enzyme activities (1 of 16, 6.3%). Significant dose differences between dogs with adverse events (n = 11; median, 2.9 mg/kg/d; range, 1.8–3.6 mg/kg/d) and dogs without adverse events (n = 81; median, 1.6 mg/kg/d; range, 0.8–4.3 mg/kg/d) were found (P < 0.001). Treatment response could be evaluated in 17 dogs. Of these 17 dogs, 12 dogs (70.5%) had an apparent positive response to the use of leflunomide. There was no significant difference (P = 0.22) in dosages between dogs that responded to leflunomide (n = 12; median, 1.9 mg/kg/d; range, 1.0–3.5 mg/kg/d) and those that did not respond (n = 5; median, 1.7 mg/kg/d; range, 1.0–2.0 mg/kg/d).

Conclusions and Clinical Importance

Results suggest that the starting dosage of leflunomide should be 2 mg/kg/d rather than the currently suggested dosage of 3–4 mg/kg/d.

On dihydroorotate dehydrogenases and their inhibitors and uses

Proper nucleosides availability is crucial for the proliferation of living entities (eukaryotic cells, parasites, bacteria, and virus). Accordingly, the uses of inhibitors of the de novo nucleosides biosynthetic pathways have been investigated in the past. In the following we have focused on dihydroorotate dehydrogenase (DHODH), the fourth enzyme in the de novo pyrimidine nucleosides biosynthetic pathway. We first described the different types of enzyme in terms of sequence, structure, and biochemistry, including the reported bioassays. In a second part, the series of inhibitors of this enzyme along with a description of their potential or actual uses were reviewed. These inhibitors are indeed used in medicine to treat autoimmune diseases such as rheumatoid arthritis or multiple sclerosis (leflunomide and teriflunomide) and have been investigated in treatments of cancer, virus, and parasite infections (i.e., malaria) as well as in crop science.