隔日使用硫唑嘌呤和糖皮质激素治疗犬皮肤病的肝毒性和骨髓抑制患病率

王帆

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

 

作者：Aurrielle C. Eberhardy | Nicole A. Heinrich | Rendina A. McFadden | Lisa V. Reiter

翻译：叶精精

 

Abstract  

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 40days, 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 105days.

Conclusions and clinical relevance: Alternate-day AZA administration with tapering glucocorticoids was well-tolerated in dogs with dermatological conditions.

摘要

背景: 硫唑嘌呤 (AZA) 因潜在的肝毒性和骨髓抑制在犬中的使用受到限制。

假设/目的: 确定接受隔日 AZA 治疗的皮肤病患犬中 AZA 相关肝毒性的发生率。假设与每日接受 AZA 的犬的已发表数据相比，接受 AZA 隔日一次 (EOD) 的犬的肝毒性发生率较低。次要目的是确定相同时间段和同一群体中 AZA 相关骨髓抑制的发生率。

动物: 41只接受AZA EOD 和糖皮质激素治疗的有皮肤疾病的家养犬，并对接受了至少两个月AZA治疗的患犬进行临床和血液学复诊。

方法:回顾性分析1994年4月至2020年7月资料。将丙氨酸转移酶(ALT)至少高于参考范围上限值2倍，定义为具有肝毒性。

结果: 在41只犬中的2只 (4.9%) 分别在18天和40天观察到与硫唑嘌呤相关的肝毒性。一只犬接受1.9 mg/kg EOD 的AZA，ALT 升高4倍。另一只犬(AZA剂量2.3 mg/kg EOD)，ALT 升高30倍。所有犬均为出现与硫唑嘌呤有关的血小板减少症、贫血或中性粒细胞减少症。1只犬 (2.4%)在105天出现淋巴细胞减少。

结论和临床相关性: 在皮肤病患犬中，AZA隔日给药联合逐渐减量的糖皮质激素耐受良好。

 

INTRODUCTION

引言

The purine analogue azathioprine (AZA) is used as an immunosuppressive medication in dogs for the treatment of a variety of immune-mediated conditions including:

pemphigus complex,inflammatory bowel disease, immune-mediated haemolytic anaemia(IMHA), immune-mediated thrombocytopenia (ITP) and cutaneous vasculitis. It can be used as a sole therapy or concurrently with other immunosuppressive medications such as glucocorticoids.

嘌呤类似物硫唑嘌呤 (AZA) 在犬中用作免疫抑制药物，用于治疗多种免疫介导疾病，包括：多类型天疱疮、炎性肠病、免疫介导的溶血性贫血 (IMHA)、免疫介导性血小板减少症 (ITP) 和皮肤血管炎。可单独治疗或与糖皮质激素等其他免疫抑制药物同时使用。

 

Dose-dependent hepatotoxicity limits the use of AZA in dogs. It typically occurs in the first 30days of therapy with a median onset of two weeks. This hepatotoxicity is defined as a twofold increase in alanine aminotransferase (ALT) above the upper limit of the reference interval. It has been reported in 15% of dogs receiving daily AZA. Many dogs receiving AZA also receive glucocorticoids, which can increase certain liver enzymes. This concurrent use can make interpretation of liver enzyme elevations challenging.

AZA有剂量依赖性肝毒性，因此其在犬中使用受到限制。它通常发生在治疗的早期30天，中位发作时间为2周。肝毒性定义为丙氨酸转移酶 (ALT) 比参考范围上限高2倍。在接受每日 AZA 的犬中，15%的犬报告了肝毒性。许多使用 AZA的犬也同时使用了能让使某些肝酶升高的糖皮质激素。这种联合用药使肝酶升高的解释具有挑战性。

 

The clinicians in our practice observed that dogs receiving AZA every other day (EOD) have a lower prevalence of hepatotoxicity compared to published data for dogs receiving daily AZA. This is logical given that the most common AZA-related hepatotoxicity is dose-dependent, rather than idiosyncratic. The objective of this study was to determine whether our clinical impression of reduced prevalence of AZA hepatotoxicity was accurate. Prevalence of AZA-associated myelosuppression in these dogs was investigated as a secondary aim.

临床医生在诊疗中观察到，与已发表的接受每日 AZA 的犬数据相比，接受隔日一次(EOD) AZA 的犬肝毒性发生率较低。考虑到最常见的与 AZA 相关肝毒性具有剂量依赖性，而不是特异性，这是合乎逻辑的。本研究的目的是确定我们对 AZA 肝毒性患病率降低的临床印象是否准确。次要目的是研究犬中 AZA 相关骨髓抑制的患病率。

 

MATERIALS AND METHODS 

材料和方法

Ethical considerations were not required for this retrospective study.

回顾性研究不需要伦理考虑。

 

Client-owned dogs receiving AZA for any dermatological indication were identified by reviewing digital medical records at a private referral dermatology clinic, between April 1994 and July 2020. Information collected from medical records included signalment, weight, dermatological diagnosis for which AZA was prescribed, initial dose of AZA with any dose adjustments, initial dose of glucocorticoids with any dose adjustments and administration of other medications. Initial and follow-up clinicopathological information included alkaline phosphatase (ALP), ALT, glucose, albumin and blood urea nitrogen (BUN), and complete blood count (CBC) for a minimum of the first two months of treatment. Medication adverse effects, changes in therapy and response were recorded. Additional data were obtained from primary veterinary clinics as needed.

通过审查1994年4月至2020年7月期间私人转诊皮肤病诊所的数字病历，确定了所有因皮肤疾病接受AZA治疗的家养犬。从病历中收集的信息包括特征、体重、皮肤学诊断、开具 AZA的处方、AZA初始剂量及任何剂量调整、糖皮质激素初始剂量及任何剂量调整和其他药物给药。初始和随访临床病理学信息包括治疗前两个月的碱性磷酸酶 (ALP)、ALT、葡萄糖、白蛋白和血尿素氮 (BUN) 以及全血细胞计数 (CBC)。记录药物不良反应、治疗变化和疗效。根据需要从初级兽医诊所获得其他数据。

 

Inclusion criteria 

入选标准

Dogs were included in the study if they met the following criteria: (i) AZA was only administered EOD; (ii) duration of therapy was a minimum of two months; (iii) a minimum of one dermatological examination and two haematological and serum chemistry panels had been performed; and (iv) a stable or tapering glucocorticoid dose if used, or if increased, no development of hepatotoxicity. Tapering was defined as the gradual reduction of glucocorticoids over a prolonged period and was performed differently for each dog according to the clinician's discretion.

如果犬符合以下标准，则将其纳入研究：(i)AZA仅EOD给药；(ii) 治疗持续时间至少为2个月；(iii) 至少进行一次皮肤病学检查以及两次血液学和血清生化检查； (iv) 和稳定或逐渐减量的糖皮质激素剂量（如果使用），或者如果增加，未发生肝毒性。逐渐减量定义为长期逐渐减少糖皮质激素，并根据临床医生的判断对每只犬进行不同的减量。

 

Exclusion criteria 

排除标准

Dogs were excluded from the study if they failed to meet the above criteria. Any animals receiving concurrent medications known to affect ALT levels were excluded if persistent ALT elevations occurred. Dogs with a known history of liver disease also were excluded.

如果犬不符合上述标准，则将其从研究中排除。如果发生持续性 ALT 升高，则排除接受已知会影响 ALT 水平的伴随药物的任何动物。还排除了已知有肝病史的犬。

 

Statistical methods 

统计方法

All glucocorticoid doses were converted to their prednisone equivalencies. Dogs were considered to develop hepatotoxicity if their serum ALT increased from within the reference interval to at least twofold above the high end of the reference interval. Azathioprineassociated hepatotoxicity was distinguished from glucocorticoid-associated hepatotoxicity by normalization of the ALT after reduction of the glucocorticoid dose and by using the Naranjo adverse drug reaction scale to determine probability of AZA as a cause of hepatotoxicity.

将所有糖皮质激素剂量转换为泼尼松当量。如果血清 ALT 从参考区间内升高至参考区间上限的至少两倍，则认为犬发生肝毒性。硫唑嘌呤相关肝毒性与糖皮质激素相关肝毒性的区别在于减少糖皮质激素剂量后 ALT 恢复正常，并使用 Naranjo药物不良反应评分表评价 AZA 确定作为肝毒性原因的概率。

 

RESULTS 

结果

The electronic search identified 106 dogs, 41 of which met the inclusion criteria. Demographic, diagnosis and medication dose information are presented in Table 1. Twenty-three of 41 dogs were receiving glucocorticoids at the time AZA was started and in 18 dogs glucocorticoid administration was begun at the same time as AZA. The glucocorticoid dose was increased in six of 41 dogs within two months of beginning AZA; none of these patients developed biochemical evidence of hepatotoxicity.

电子检索识别出106只犬，其中41只符合入选标准。统计学、诊断和药物剂量信息见表1。41只犬中的23只在开始 AZA 治疗时正在接受糖皮质激素治疗，18只犬在开始 AZA 治疗的同时开始糖皮质激素治疗。在开始 AZA 治疗的两个月内，41只犬中的6只增加了糖皮质激素的剂量；这些患犬均未出现肝毒性的生化证据。

 

Hepatotoxicity occurred in 14 of 41 dogs (34%). Two dogs had AZA-associated hepatotoxicity, 11 dogs had glucocorticoid-associated hepatotoxicity, one dog had fluconazole-associated hepatotoxicity. All dogs with hepatotoxicity were receiving a tapering dose of glucocorticoids, with a median starting dose of 1.3 mg/kg/day (range 0.5–11.5 mg/kg) and a median AZA dose of 1.9 mg/kg EOD (range 1.5–2.6 mg/ kg). Among dogs with hepatotoxicity, ALT increased by a median of sixfold (range 1.7–41). Hepatotoxicity was observed with a median time of 15 days. Despite observation of biochemical hepatotoxicity, all animals appeared clinically healthy and had no physical examination evidence of liver disease such as ascites or jaundice.

41只犬中有14只 (34%) 发生肝毒性。2只犬出现 AZA 相关肝毒性，11只犬出现糖皮质激素相关肝毒性，1只犬出现氟康唑相关肝毒性。所有肝毒性犬均接受逐渐减量的糖皮质激素，中位起始剂量为1.3 mg/kg/天（范围0.5-11.5 mg/kg），中位 AZA 剂量为1.9 mg/kg EOD（范围1.5-2.6 mg/kg）。在肝毒性犬中，ALT中位增加6倍（范围1.7-41）。观察到肝毒性的中位时间为15天。尽管观察到生化肝毒性，但所有动物在临床上均健康，且无临床肝病（如腹水或黄疸）的体格检查证据。

 

The dose of glucocorticoids was reduced for dogs with hepatotoxicity according to the clinician's discretion. In the majority of cases (11 of 14), ALT elevation resolved by this method alone with an average of 58% reduction in glucocorticoids (range 25%– 100%), with stable AZA EOD doses. Of the three remaining cases, ALT did not return to the reference interval after lowering the glucocorticoid dose. One of these cases required discontinuation of concurrent fluconazole that was being used to treat secondary yeast dermatitis before resolution of ALT elevation. According to the Naranjo adverse drug reaction probability scale, AZA adverse drug reaction leading to hepatotoxicity was observed in the two remaining cases (4.9%).

对于肝毒性犬，根据临床医生的判断减少糖皮质激素的剂量。在大多数病例 (11/14) 中，单独使用该方法 ALT 升高改善，糖皮质激素平均减少58%（范围25%-100%），AZA 隔日一次剂量稳定用药。在其余3例病例中，降低糖皮质激素剂量后，ALT未恢复至参考区间。其中1例病例需要在停用正在用于治疗继发性酵母性皮炎的氟康唑后 ALT 升高改善。根据 Naranjo药物不良反应评分表，其余2例 (4.9%)判断确认为AZA 药物不良反应导致的肝毒性。

 

One of the two dogs that developed AZA-associated hepatotoxicity was a 6-year-old neutered male Boxer mix. He was being treated for pemphigus foliaceus (PF) with AZA 1.9  mg/kg EOD and prednisone equivalent 0.5  mg/kg/day tapering dose. A fourfold increase in ALT (346 IU/L) was noted 18 days after AZA initiation, which resolved on subsequent biochemistry panels after the addition of S-Adenosyl methionine (SAMe) supplementation. The other dog that developed AZA-associated hepatotoxicity was a 6-year-old neutered male Australian cattle dog mix. He also was being treated for PF with an initial AZA dose of 1.5 mg/kg EOD and prednisone 1.2 mg/kg/ day tapering dose. After 22 days of therapy, there was minimal clinical improvement and normal serum biochemical and haematological values, so the AZA dose was increased to 2.3 mg/kg EOD on Day (D)26 while continuing the prednisone taper. A 30-fold increase in ALT (2487 IU/L) was detected on D40 after AZA initiation (14 days after the dose increase), which resolved on subsequent biochemistry panels with the reduction of AZA back to 1.5 mg/kg EOD. These dogs scored a three and four, respectively, on the Naranjo adverse drug reaction probability scale, indicating a possible association with AZA. Concurrent elevation of ALP 6.9-fold (910 IU/L) and 6.7-fold (830 IU/L), respectively, was seen in each dog. Neither of these dogs had other biochemical or haematological changes outside the normal reference ranges. Detectable differences were not identified in these two dogs compared with dogs who did not develop hepatotoxicity with respect to sex, breed, age, dosage of AZA or glucocorticoid initial dosage.

发生AZA相关肝毒性的两只犬中的一只是6岁去势雄性拳师犬串。他正在接受AZA 1.9 mg/kg EOD和等同于泼尼松0.5 mg/kg/天逐渐减量治疗落叶型天疱疮(PF)。AZA 治疗开始后18天，观察到 ALT 升高4倍 (346 IU/L)，在添加 S-腺苷蛋氨酸 (SAMe) 补充剂后，在随后的生化检查中消退。发生 AZA 相关肝毒性的另一只犬是6岁去势雄性澳大利亚牧牛犬串。他还在进行 PF 治疗，AZA初始剂量为1.5 mg/kg EOD，泼尼松1.2 mg/kg/天逐渐减量。治疗22天后，临床改善极小，血清生化和血液学值正常，因此在第26天将 AZA 剂量增加至2.3 mg/kg EOD，同时继续泼尼松减量。在 AZA 开始给药后第40天（剂量增加后14天）检测到 ALT 升高30倍 (2487 IU/L)，AZA降低至1.5 mg/kg EOD，随后的生化检查中改善。这些犬在Naranjo药物不良反应评分分别得3分和4分，表明可能与 AZA 相关。在每只犬中同时观察到 ALP 分别升高6.9倍 (910 IU/L) 和6.7倍 (830 IU/L)。这些犬均未出现超出正常参考范围的其他生化或血液学变化。与未发生肝毒性的犬相比，这两只犬在性别、品种、年龄、AZA剂量或糖皮质激素初始剂量方面未发现可检测到的差异。

 

Myelosuppression also was evaluated. Three dogs (7.3%) showed thrombocytopenia (141, 155 and 161×103 platelets/μL) with a median onset of 29days (range 14–42days), although all dogs also had platelet clumping, and therefore, the decreases were not considered pathological. One dog (2.4%) developed transient leukopenia (3.9 ×103 leucocytes/μL) characterized by lymphopenia (585 lymphocytes/μL) on D60. Subsequent CBC panels showed no abnormal values. Therefore, these dogs did not meet the Naranjo criteria for an AZA adverse drug reaction.

还评价了骨髓抑制。3只犬 (7.3%) 出现血小板减少（141、155和161 × 103血小板/μL），中位发作时间为29天（范围14-42天），所有犬出现血小板聚集，因此，认为血小板减少不是病理性的。D60 时，1只犬 (2.4%) 出现一过性白细胞减少（3.9 × 103白细胞/μL），其特征为淋巴细胞减少（585淋巴细胞/μL）。随后的 CBC 检查未显示异常值。因此，这些犬不符合 AZA 药物不良反应的Naranjo标准。

 

Between two and 24months after starting AZA, haematological parameters were available for 28 dogs. None of these dogs showed new biochemical evidence of hepatotoxicity. The only cytopenia observed was in one dog receiving AZA 2.5 mg/kg EOD. This dog developed new onset leukopenia (3.3 ×103 leucocytes/μL) characterized by lymphopenia (429 lymphocytes/μL) on D105, requiring a 33% AZA dose reduction before resolution was noted. This patient's prednisone was discontinued 42days before development of the leukopenia; thus, AZA was the only drug being administered at that time, indicating a possible association.

在开始 AZA 治疗后2-24个月，28只犬的血液学参数可用。这些犬均未显示肝毒性的新生化证据。在接受AZA 2.5 mg/kg EOD的1只犬中观察到唯一的血细胞减少。该犬在第105天出现新生白细胞减少（3.3 × 103白细胞/μL），特征为淋巴细胞减少（429淋巴细胞/μL），在观察到改善前需要降低 33%AZA 剂量。该患犬在发生白细胞减少症前42天停用泼尼松；因此，AZA是当时给予的唯一药物，表明可能相关。

 

The number of dogs that developed AZA hepatotoxicity (n = 2) or AZA myelosuppression (n = 1) was so low that statistical analysis was not performed.

发生 AZA 肝毒性 (n = 2) 或 AZA 骨髓抑制 (n = 1) 的犬数量太少，因此未进行统计分析。

 

DISCUSSION 

讨论

Azathioprine-associated hepatotoxicity was observed in 4.9% of dogs. This prevalence is approximately one-third of that reported in dogs receiving daily AZA (15%). Hepatocellular liver injury was evident without development of clinical illness. Azathioprine-associated hepatoxicity developed 18 and 40days after beginning therapy. In one study of 34 dogs, AZA-associated hepatotoxicity occurred after 13–22days of daily AZA with a median onset of two weeks. Although hepatotoxicity was not documented after the two-month observation period, biochemistry panels were available only for 28 of 41 dogs; therefore, delayed AZA toxicity cannot be excluded. Monitoring of haematological and serum chemistry panels has been recommended before starting therapy and every two weeks thereafter for two months, then every one to two months during the course of AZA therapy. The timing of hepatoxicity in this study supports these serial monitoring recommendations.

在4.9%的犬中观察到硫唑嘌呤相关肝毒性。该患病率约为每日接受 AZA 犬报告的患病率 (15%) 的三分之一。肝细胞肝损伤明显，未发生临床疾病。在开始治疗后18天和40天发生硫唑嘌呤相关肝毒性。在一项34只犬的研究中，每日 AZA 给药13-22天后发生 AZA 相关肝毒性，中位发生时间为2周。尽管在2个月观察期后未记录肝毒性，但仅28/41只犬的生化检查可用；因此，不能排除迟发性 AZA 毒性。建议在开始治疗前监测血液学和血清生化检查，此后每两周监测一次，持续2个月，然后在 AZA 治疗过程中每1-2个月监测一次。本研究中的肝毒性时间支持这些系列监测建议。

 

To the best of the authors' knowledge, this is the only study evaluating hepatoxicity occurrence with EOD use of AZA in dogs for treatment of autoimmune skin diseases. The clinicians in our practice feel that AZA administered EOD in combination with tapering glucocorticoids is adequate to induce remission of autoimmune skin diseases, in particular PF. More studies are needed to determine whether remission in dogs with autoimmune haematological or gastrointestinal diseases could be achieved with AZA EOD. The frequency of AZA dosing to achieve remission may be reduced in dogs with autoimmune dermatological disease compared to those with autoimmune haematological or gastrointestinal disease, as a result of changes in drug absorption, distribution or other unidentified factors. Future studies should include evaluation of efficacy of EOD AZA for the treatment of dermatological diseases.

据作者所知，这是唯一一项评价犬隔日一次使用 AZA 治疗自身免疫性皮肤病的肝毒性发生的研究。我们实践中的临床医生认为隔日一次AZA联合逐渐减量的糖皮质激素足以诱导自身免疫性皮肤病的缓解，尤其是PF。需要更多的研究来确定隔日一次AZA是否可以在自身免疫性血液学或胃肠道疾病犬中达到缓解。与自身免疫性血液学或胃肠道疾病犬相比，由于药物吸收、分布或其他未识别因素的变化，自身免疫性皮肤病犬中 AZA 给药达到缓解的频率可能降低。未来的研究应包括评价隔日一次AZA治疗皮肤病的疗效。

 

Disproportionate representation of hepatoxicity in German shepherd dogs was demonstrated in one study of dogs receiving daily AZA at standard therapeutic doses with variable dosages of glucocorticoids. This variance highlights possible differences in breed-related AZA activation or elimination. High-activity polymorphisms in the TPMT pathway in humans increase the concentrations of 6-methylmercaptopuine (6-MMP), resulting in a higher risk of hepatotoxicity. The exact pathways of hepatotoxicity in canine patients receiving AZA merit further investigation.

在一项犬每日接受标准治疗剂量 AZA 和不同剂量糖皮质激素的研究中，证实了德国牧羊犬中肝毒性的不成比例表现。这种差异突出了品种相关 AZA 活化或消除的可能差异。人类 TPMT 通路的高活性多态性增加了6-甲基巯基嘌呤 (6-MMP) 的浓度，导致肝毒性的风险更高。接受 AZA 的犬肝毒性的确切途径值得进一步研究。

 

Azathioprine-associated hepatocyte necrosis has been linked to reduction of glutathione; an antioxidant normally found in abundance in hepatocytes that is depleted during the first step of AZA biotransformation. An excess of glutathione, water-soluble vitamin E analogues or N-acetylcysteine are protective against AZA-associated hepatocyte necrosis. In this study a SAMe supplement was used in one dog that developed hepatotoxicity. Although ALT returned to the normal reference range within two weeks, it is unclear if the SAMe supplement or continued tapering of the glucocorticoid dose caused the normalization. The efficacy of SAMe in dogs with AZA hepatotoxicity is unknown, and further studies are warranted.

硫唑嘌呤相关的肝细胞坏死与谷胱甘肽的减少有关；谷胱甘肽是一种通常在肝细胞中大量存在的抗氧化剂，在 AZA 生物转化的第一步中被耗尽。补充谷胱甘肽、水溶性维生素 E 类似物或 N-乙酰半胱氨酸可预防 AZA 相关的肝细胞坏死。在本研究中，1只发生肝毒性的犬使用 SAMe 补充剂。尽管 ALT 在两周内恢复至正常参考范围，但尚不清楚是SAMe补充剂，还是继续逐渐减少糖皮质激素剂量使结果正常。SAMe在AZA肝毒性犬中的疗效尚不清楚，需要进一步研究。

 

Azathioprine-associated neutropenia or thrombocytopenia were not noted. In one study of 48 dogs receiving daily AZA, the median time for neutropenia or thrombocytopenia or both to develop was 53days (range 45–196days), with a prevalence of 8%. One dog in the present study developed lymphopenia with an onset of 105days, requiring a 33% reduction in AZA before resolution was noted. This shows that continued monitoring of the CBC every one to two months during the course of AZA therapy is important.

未观察到硫唑嘌呤相关的中性粒细胞减少或血小板减少。在一项48只接受每日 AZA 治疗的犬研究中，中性粒细胞减少或血小板减少或两者发生的中位时间为53天（范围45-196天），患病率为8%。本研究中的1只犬在105天发生淋巴细胞减少，在观察到消退前需要降低33% AZA。这表明在 AZA 治疗过程中每1-2个月持续监测 CBC 非常重要。

 

There were multiple limitations of the present study. As this is a retrospective study, haematological and biochemical values were not available at regular time intervals and samples were collected at most on a bi-weekly basis for the initial two-month period. The precise time at which hepatotoxicity developed could not be determined owing to lack of clinical signs of hepatotoxicity and lack of consistent biochemical data timing. The small number of dogs included in the study and the small number that developed hepatotoxicity precluded analysis of predisposing factors such as breed, age and sex. A larger dataset may allow additional conclusions to be made about factors affecting AZA-associated hepatotoxicity and myelosuppression in dogs.

本研究存在多种局限性。由于这是一项回顾性研究，无法定期获得血液学和生化值，因此在最初的2个月期间，最多每两周采集一次样本。由于缺乏肝毒性的临床症状和缺乏一致的生化数据时间，无法确定发生肝毒性的确切时间。研究中纳入的犬数量较少，发生肝毒性的犬数量较少，无法分析易感因素，如品种、年龄和性别。更大的数据集可能允许对影响犬中 AZA 相关肝毒性和骨髓抑制的因素得出额外的结论。

 

Another limitation is that all the dogs included in the study received glucocorticoids in addition to AZA. It is common practice to administer these medications together in canine dermatological patients, particularly for treatment of PF. This concurrent use complicates evaluation of biochemical value abnormalities. It has been shown that glucocorticoid use in dogs can cause serum ALT elevations. This elevation may be secondary to membrane alterations as a result of cell swelling and possible retention of bile acids. To minimize the effects of glucocorticoids on the study, only dogs that were receiving stable or tapering glucocorticoids during the first two months of AZA therapy were included, or if hepatotoxicity was not noted after an increased dose of glucocorticoids. Despite these limiting parameters, glucocorticoid hepatotoxicity still was common in this study. Eleven dogs (27%) developed hepatotoxicity that resolved with an average of 58% glucocorticoid dose reduction and no change in AZA dosing. One of these dogs was a shih tzu with PF that received an outlier glucocorticoid dose of 5.75mg/ kg twice daily (11.5 mg/kg/day). The dose was reduced to 5 mg/kg/day by D3 and to 1.3 mg/kg EOD on D14. This dog developed transient ALT elevations consistent with hepatotoxicity on D14 which resolved by D32 after tapering glucocorticoid doses, despite continuation of a stable AZA dose (1.9 mg/kg EOD).

另一个局限性是研究中纳入的所有犬除 AZA 外还接受了糖皮质激素治疗。在皮肤病患犬经常同时给予这些药物，尤其是用于治疗PF。这种联合用药使生化值异常的评价变得复杂。有研究表明，犬使用糖皮质激素可引起血清 ALT 升高。这种升高可能继发于细胞膜改变、细胞肿胀和胆汁酸可能潴留的结果。为尽量减少糖皮质激素对研究的影响，仅纳入在 AZA 治疗的前两个月内接受稳定或逐渐减量糖皮质激素的犬，或者在增加糖皮质激素剂量后未观察到肝毒性的犬。尽管有这些限制参数，糖皮质激素肝毒性在本研究中仍然很常见。11只犬 (27%) 发生肝毒性，平均糖皮质激素剂量降低58%后消退，AZA给药无变化。其中1只犬为患 PF的西施犬，接受高剂量糖皮质激素5.75 mg/kg每日两次（11.5 mg/kg/天）。D3 时剂量降至 5 mg/kg/天，D14时降至1.3 mg/kg EOD。该犬在 D14 发生了与肝毒性一致的一过性 ALT升高，在逐渐减少糖皮质激素剂量后D32恢复，但持续使用相同剂量的AZA(1.9 mg/kg EOD)。

 

For the two dogs in our study that developed AZA associated hepatotoxicity, it is unlikely that glucocorticoids could have caused this change because they were not receiving daily high-dose glucocorticoids. In one study a 34.6% increase in serum ALT was noted by D14 of 1 mg/kg/day glucocorticoid therapy in dogs, which resolved with tapering to EOD use or stopping the glucocorticoids. The glucocorticoids for the dogs in our study already had been tapered to EOD, on D8 and D26, respectively, before the development of hepatotoxicity. Additionally, the AZA dose administered to the Australian cattle dog mix had been increased on D26 making dose-dependent AZA hepatotoxicity more likely.

对于我们研究中发生 AzA相关肝毒性的两只犬，糖皮质激素不太可能引起这种变化，因为其未每日接受高剂量糖皮质激素。在一项研究中，在犬接受 1 mg/kg/天糖皮质激素治疗的 D14 时观察到血清 ALT 升高34.6%，逐渐减少 EOD 使用或停用糖皮质激素后消退。在我们的研究中，犬的糖皮质激素在发生肝毒性前已分别在 D8 和 D26 逐渐减量至EOD。此外，D26时给予澳大利亚牧牛犬串的 AZA 剂量增加，使剂量依赖性 AZA 肝毒性的可能性更大。

CONCLUSIONS 

结论

As anticipated, AZA-associated hepatotoxicity was much less common in dogs receiving it EOD. Frequent monitoring of serum biochemistry and CBC panels still is warranted. Further investigation into the mechanism and AZA-associated hepatotoxicity is needed.

正如预期那样，AZA相关肝毒性在接受 EOD 的犬中不太常见。仍然需要频繁监测血清生化和CBC检查。需要进一步研究 AZA 相关肝毒性的机制。

 

 

 

 

 

TABLE 1 Signalment data for dogs treated with azathioprine (AZA) every other day (EOD) and glucocorticoids, with clinical follow-up, from 1994 to 2020, separated into those that did and did not develop AZA hepatotoxicity

表1 1994年至2020年临床随访期间接受硫唑嘌呤 (AZA) 隔日一次 (EOD) 和糖皮质激素治疗的犬的临床数据，分为发生和未发生 AZA 肝毒性的犬

	发生AZA肝毒性的犬 (n=2)	未发生AZA肝毒性的犬 (n=39)
年龄（年）	6.0	6.0 (1.0–13.0)
性别	FS (0) FI (0) MN (2) MI (0)	FS (22) FI (1) MN (15) MI (1)
品种	拳师犬串 (1) 澳大利亚牧牛犬串 (1)	拉布拉多(7) 拉布拉多串(3) 英国斗牛犬(3) 西施犬(3)   德国牧羊犬串 (2) 比格犬串(1) 边境牧羊犬(1) 威尔士柯基 (1) 查理王小猎犬 (1) 吉娃娃 (1) 腊肠犬串 (1) 英国斗牛犬串 (1) 英国史宾格犬 (1) 金毛寻回犬(1) 金毛寻回犬串 (1) 金毛贵宾串 (1) 灵缇犬 (1) 拉布拉多贵宾串 (1) 比特犬串(1) 雪纳瑞贵宾串(1) 牧羊犬串（未说明） (1) 日本柴犬(1) 西施犬串 (1) 史宾格犬(1) 标准贵宾犬(1) 未知杂交犬(1)
基础诊断	落叶型天疱疮(2)	落叶型天疱疮 (37) 寻常型天疱疮(1) 血管炎（缺血性皮肤病）(1)
AZA剂量(mg/kg EOD)	2.1 (1.9–2.3)	2.0 (0.8–3.6)
泼尼松或等效初始剂量（mg/kg/天）	0.9 (0.5–1.2)	1.1 (0.2–11.5)

Note: Data are reported as medians with ranges.

Abbreviations: FI, female intact; FS, female spayed; MI, male intact; MN, male neutered.

注意:报道数据为中位值带范围。
缩写:FI：未绝育雌性;FS：已绝育雌性;MI：未去势雄性;MN：已去势雄性。

 

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