アザチオプリン
Azathioprine
Azathioprine / Azathioprine Sodium
別名: Imuran · Azasan · Azathioprinum · BW-57322 · NSC-39084
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Inflammatory bowel disease | Initially 2 mg/kg PO once daily for 2 weeks, then tapered to 2 mg/kg PO every other day for 2-4 weeks, then 1 mg/kg PO every other day. | PO | q24h then tapered | Long-term | 🌎 NA |
| Immune-mediated anemia, colitis, immune-mediated skin disease, and acquired myasthenia gravis | 2 mg/kg PO once daily (q24h); long-term therapy 0.5-1 mg/kg PO every other day | PO | q24h then q48h | Long-term | 🌎 NA |
| Adjunctive therapy in myasthenia gravis in non-responsive patients | Initially, 1 mg/kg PO once daily. If neutrophil and platelet counts are normal after 2 weeks, dose is increased to 2 mg/kg PO once daily. | PO | q24h | Until clinical remission | 🌎 NA |
| Lymphoplasmacytic enteritis (if poor response to prednisolone) | 2 mg/kg PO once daily for 5 days, then on alternate days to prednisolone | PO | q24h then q48h | Long-term | 🌎 NA |
| Severe cases of immune-mediated hemolytic anemia (IMHA) | 2.2 mg/kg PO once daily (q24h) | PO | q24h | Long-term | 🌎 NA |
| Acute immune-mediated hemolytic anemia (IMHA) with glucocorticoids | 1-2 mg/kg PO once daily | PO | q24h | Long-term maintenance | 🌎 NA |
| Severe and refractory inflammatory bowel disease | 2.2 mg/kg PO once daily | PO | q24h | Long-term | 🌎 NA |
| Adjunctive treatment of ocular fibrous histiocytomas | 2 mg/kg PO daily for 2 weeks, reevaluate, and reduce to 1 mg/kg every other day for 2 weeks, then 1 mg/kg once weekly for 1 month | PO | Tapering schedule | 10 weeks | 🌎 NA |
| Prevention of rejection of MHCmatched renal allografts (with cyclosporine) | 1-5 mg/kg PO every other day | PO | q48h | Long-term | 🌎 NA |
| Perianal fistulas (anal furunculosis) | Initially 2 mg/kg PO once daily (q24h)... Then reduce to 2 mg/kg PO every other day (q48h) and continued for 12 weeks... After 12 weeks, reduce dose to 1 mg/kg PO every other day (q48h) | PO | Tapering schedule | 12 months | 🌎 NA |
| Glomerulonephritis | 2 mg/kg PO once daily | PO | q24h | Unspecified | 🌎 NA |
| Chronic hepatitis (to reduce inflammation) | 2.2 mg/kg PO once daily in combination with corticosteroids... Azathioprine dose is given every other day after 1-2 weeks. | PO | q24h then q48h | Long-term | 🌎 NA |
| Immune-mediated diseases (e.g., IMHA, polyarthritis) | 2 mg/kg p.o. q24h for a maximum of 2-3 weeks, then 0.5-2 mg/kg p.o. q48h | PO | q24h initially, then q48h | Max 2-3 weeks for initial q24h dosing, then maintenance | 🌍 EU |
- Inflammatory bowel disease: May take 2-6 weeks before beneficial effects are seen.
- Immune-mediated anemia, colitis, immune-mediated skin disease, and acquired myasthenia gravis: With prednisolone administered on the alternate days.
- Adjunctive therapy in myasthenia gravis in non-responsive patients: Taper to every other day when clinical remission occurs. Discontinue if WBC <4,000 cells/mcL or neutrophils <1,000 cells/mcL.
- Severe cases of immune-mediated hemolytic anemia (IMHA): In addition to prednisone. Tapered gradually.
- Acute immune-mediated hemolytic anemia (IMHA) with glucocorticoids: Used for long-term maintenance as steroid side effects become intolerable.
- Severe and refractory inflammatory bowel disease: A lag time of 3-5 weeks is expected before clinical improvement is noted.
- Perianal fistulas (anal furunculosis): Dose reduced based on clinical response or myelosuppression markers.
- Glomerulonephritis: Immunosuppressive treatment is controversial.
- Immune-mediated diseases (e.g., IMHA, polyarthritis): Often used in conjunction with corticosteroids. Clinical response may take up to 6 weeks.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Severe and refractory inflammatory bowel disease | 0.3 mg/kg PO once every other day | PO | q48h | Long-term | 🌎 NA |
| Immune-mediated diseases | Not recommended | PO | Not recommended | Not recommended | 🌍 EU |
- Severe and refractory inflammatory bowel disease: Must be used with extreme caution due to myelotoxicity. May take 3-5 weeks for beneficial effects.
- Immune-mediated diseases: Cats often develop severe, non-responsive fatal leucopenia and thrombocytopenia.
フェレット
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Inflammatory bowel disease | 0.9 mg/kg PO q24-72h | PO | q24-72h | Unspecified | 🌎 NA |
- Inflammatory bowel disease: Used alongside prednisone and dietary management.
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Immunosuppressive | 3 mg/kg PO q24h | PO | q24h | Unspecified | 🌎 NA |
| Autoimmune skin diseases (e.g., pemphigus foliaceous) | 13 mg/kg PO q24h for 1 month, then every other day (q48h) | PO | q24h then q48h | Long-term | 🌎 NA |
- Immunosuppressive: Appears to be a relatively safe immunosuppressive treatment in the horse.
- Autoimmune skin diseases (e.g., pemphigus foliaceous): Used as a steroid-sparing drug. May cause thrombocytopenia.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
アザチオプリンは、獣医療（主に犬）において、免疫介在性溶血性貧血（IMHA）、炎症性腸疾患（IBD）、重症筋無力症、天疱瘡などの様々な免疫介在性および自己免疫疾患の治療に広く使用される強力なプリン拮抗型免疫抑制薬です。
臨床上の重要ポイント：
- ステロイド節減効果： コルチコステロイド（プレドニゾンやプレドニゾロンなど）と併用されることがよくあります。この併用により、疾患の寛解を維持しつつステロイドの用量を徐々に減らすことができ、長期的なステロイドの副作用を最小限に抑えることができます。
- 遅効性： アザチオプリンは即効性ではありません。完全な免疫抑制効果が得られるまでに通常2〜6週間かかります。そのため、急性の生命を脅かす自己免疫疾患の危機に対して単独で使用するには適していません。
- 動物種による感受性： 猫はアザチオプリンに対して非常に敏感であり、チオプリンメチルトランスフェラーゼ（TPMT）酵素のレベルが生まれつき低いため、骨髄抑制を引き起こしやすいです。猫への使用は非常に議論があり、一般的には避けられます。
- 毒性リスク： 最も重大な副作用は骨髄抑制（白血球減少症、貧血、血小板減少症）です。犬では肝毒性や急性膵炎も注目すべきリスクです。
作用機序
Azathioprine is a prodrug that must be metabolized to exert its effects.
- Pathway: Azathioprine is rapidly converted in the body (primarily in erythrocytes and the liver) to 6-mercaptopurine (6-MP).
- 6-MP is further metabolized into active thioguanine nucleotides (TGNs).
- Mechanism: These active metabolites act as purine antagonists. They are falsely incorporated into cellular DNA and RNA, which inhibits purine metabolism, RNA/DNA synthesis, and cellular mitosis.
- Immunological Effect: Because lymphocytes (T-cells and B-cells) lack a salvage pathway for purine synthesis and rely heavily on de novo synthesis, they are profoundly affected. This leads to a marked suppression of delayed hypersensitivity and cellular immunity, with a lesser effect on humoral antibody responses.
安全性・警告
禁忌
- Known hypersensitivity to azathioprine
- Cats (generally contraindicated due to severe, potentially fatal myelotoxicity)
有害事象
- Bone marrow suppression (leukopenia, anemia, thrombocytopenia)
- Gastrointestinal distress (vomiting, diarrhea, anorexia)
- Acute pancreatitis
- Hepatotoxicity
- Poor hair growth
- Increased susceptibility to secondary infections
- Increased risk of neoplastic illnesses with long-term use
注意事項
Black Box Warning Equivalent: Azathioprine is a known mutagen and teratogen. Pregnant women or those trying to conceive should avoid handling this medication. If handling is necessary, strict use of protective gloves is required.
- Hepatic Dysfunction: Use with extreme caution in patients with pre-existing liver disease, as hepatotoxicity is a known adverse effect.
- Thiopurine Methyltransferase (TPMT) Deficiency: Dogs have variable TPMT activity (similar to humans). Dogs with low TPMT activity are at a significantly higher risk for severe bone marrow suppression.
- Tapering: In recovering patients (e.g., IMHA), withdrawal of the drug must be tapered very slowly over several months. Rapid withdrawal can trigger a rebound hyperimmune response and fatal relapse.
- Pregnancy/Nursing: FDA Category D (human). Distributed into milk; use milk replacer if the dam is treated.
医薬品相互作用
Increased potential for hematologic toxicity
Decreases hepatic metabolism of azathioprine; significantly increases toxicity risk. Dose of azathioprine must be reduced to 1/4 to 1/3 of the usual dose if used concurrently.
Increased risk for azathioprine toxicity
Neuromuscular blocking activity may be inhibited or reversed by azathioprine
Often used together intentionally, but carries a greater potential risk for overall toxicity development
Increased potential for hematologic toxicity (additive bone marrow suppression)
Potential for reduced anticoagulant effect
Increased risk of azathioprine toxicity.
May increase the potential for haematological adverse events (e.g., severe anaemia or leucopenia).
監視
- Hemograms (CBC including platelets): Monitor closely; initially every 1-2 weeks, then every 1-2 months on maintenance therapy. Reduce dose by 25% if WBC drops to 5,000-7,000 cells/mcL. Discontinue if WBC < 5,000 cells/mcL until resolved.
- Liver function tests (ALT, AST, ALP, Bilirubin)
- Serum amylase/lipase (if pancreatitis is suspected)
- Clinical efficacy and signs of secondary infection
薬物動態
吸収
Poorly absorbed from the gastrointestinal tract.
分布
Rapidly taken up by lymphocytes and erythrocytes. Distributed into milk.
代謝
Rapidly metabolized to mercaptopurine (6-MP). Mercaptopurine is further metabolized to several other compounds via pathways including thiopurine methyltransferase (TPMT). Cats have naturally low TPMT activity, making them highly susceptible to toxicity.
消失
Metabolites are excreted primarily by the kidneys. Only minimal amounts of azathioprine or mercaptopurine are excreted unchanged.
過剰投与
There is limited specific information regarding acute overdose of azathioprine in veterinary patients.
- Decontamination: If ingestion was recent, use standard protocols to empty the GI tract (emesis induction, activated charcoal).
- Treatment: Provide aggressive supportive care. Monitor hematologic parameters closely for delayed bone marrow suppression.
- Consultation: Contact an animal poison control center for the most up-to-date guidance.
製品
製剤
- Tablets
- Injection (powder for reconstitution)
- Compounded oral suspension
ヒト用医薬品
- Azathioprine Tablets: 50 mg, 75 mg & 100 mg (Azasan®, Imuran®, generic)
- Azathioprine Sodium Injection: 100 mg (as sodium)/vial in 20 mL vials (generic)
規制ステータス
POM (Prescription Only Medicine). Handled under cascade using human formulations.
POM-V / POM. Handled under the prescribing cascade.
規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Tablets should be stored at room temperature in well-closed containers and protected from light. Sodium powder for injection should be stored at room temperature and protected from light; after reconstitution, it must be used within 24 hours as it contains no preservatives. Compounded oral suspensions have optimal stability between pH 5.5 and 6.5 and should be protected from light.
飼主向け情報
飼い主様への重要な情報：
- 効果が出るまで時間がかかります： この薬が効果を発揮するまでには時間がかかります。ペットの症状が改善するまでに数週間かかる場合があります。獣医師に相談せずに薬を中止しないでください。
- 安全性と取り扱い： アザチオプリンは人間のDNAに影響を与える可能性のある強力な薬です。錠剤を取り扱った後は必ず手をよく洗ってください。妊娠中、妊娠を希望している、または授乳中の方は、この薬の取り扱いを避けてください。どうしても取り扱う必要がある場合は、必ず保護手袋を着用してください。
- 副作用に注意： この薬は免疫系を抑制し、骨髄に影響を与える可能性があるため、ペットは感染症や出血のリスクが高くなります。
- 獣医師に連絡すべき症状： ペットに異常な出血、原因不明のあざ、歯茎の蒼白、発熱、食欲不振、嘔吐、下痢、または無気力などの症状が見られた場合は、すぐに獣医師に連絡してください。
- 厳密なモニタリング： 薬が骨髄や肝臓にダメージを与えていないか確認するため、ペットは（特に最初の数ヶ月間）頻繁な血液検査を受ける必要があります。予定された再診には必ずお越しください。
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