ミトキサントロン
ミトキサントロンは、犬や猫の様々な悪性腫瘍の治療に使用される合成アントラセンジオン系抗悪性腫瘍薬です。 **主な臨床応用:** * **リンパ腫:** 第一選択のプロトコル（CHOPなど）が効果を示さなくなった場合のレスキュー薬として頻繁に使用されます。 * **癌（Carcinomas）:** 移行上皮癌（TCC）、扁平上皮癌、腎腺癌、甲状腺癌に有効です。 * **肉腫（Sarcomas）:** 線維肉腫、血管周皮腫、乳腺腺癌に使用されます。 **臨床上のポイント:** * 構造的にはアントラサイクリン系（ドキソルビシンなど）に似ていますが、アミノ糖部分を持たないため、フリーラジカルの発生が大幅に減少します。これにより、ドキソルビシンよりも**心毒性が大幅に低く**なっています。 * 腎クリアランスが非常に低いため（約10％）、腎不全を患っている猫にとってドキソルビシンよりもはるかに安全な代替薬となります。 * その濃い青色と強力な効果から、獣医腫瘍学では「ブルーサンダー」と俗称されることがあります。
作用機序: Mitoxantrone exerts its cytotoxic effects through multiple mechanisms: * **DNA Intercalation:** It inserts itself between DNA base pairs, causing structural distortion. * **Electrostatic Interaction:** Nonintercalative binding to DNA further stabilizes the drug-DNA complex. * **Topoisomerase II Inhibition:** **(Pharmacological addition)** It inhibits the enzyme Topoisomerase II, preventing the religation of DNA strands and leading to double-strand DNA breaks. * **Synthesis Inhibition:** Ultimately inhibits both DNA and RNA synthesis. While it is not strictly cell-cycle phase specific, it demonstrates the highest activity during the **S phase** (DNA synthesis phase) of the cell cycle.
動物種別の用量
- Soft-tissue sarcomas · 6-6.5 mg/m2 IV given every 3-4 weeks for 4-6 treatments · IV · every 3-4 weeks · 4-6 treatments
- Effective dose (general) · 6.5 mg/m2 IV every 2-3 weeks · IV · every 2-3 weeks
- Single rescue agent for lymphoma · 6-6.5 mg/m2 IV every 3 weeks · IV · every 3 weeks
- Transitional cell carcinoma · 5 mg/m2 IV every 21 days with piroxicam (0.3 mg/kg PO once daily) · IV · every 21 days
- Lymphoma, squamous cell carcinoma, transitional cell carcinoma, mammary gland tumors, etc. · 6 mg/m2 IV every 2-3 weeks · IV · every 2-3 weeks
- Single rescue agent for lymphoma · 5.5-6 mg/m2 IV every 3 weeks · IV · every 3 weeks
- Rescue agent for canine lymphoma · 6 mg/m2 IV every 2-3 weeks · IV · every 2-3 weeks · Check CBC on day 7 after treatment and the protocol can be repeated on day 14 or 21 if the dog attains complete or partial response. Combining with DTIC (dacarbazine) may improve response rate.
- Transitional cell carcinoma after laser ablation of the primary tumor · 5 mg/m2 IV every 3 weeks for 4 treatments · IV · every 3 weeks · 4 treatments · Piroxicam was given at a dosage of 0.3 mg/kg PO once daily for the remaining life of the dog.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Severe pre-existing myelosuppression
- Concurrent active infection
- Significantly impaired cardiac function
- Patients with prior extensive cytotoxic drug or radiation exposure (relative)
- Pregnancy (FDA Category D) and nursing mothers
- Pre-existing myelosuppression
- Concurrent infection
- Hepatic disease
- Impaired cardiac function
有害事象
- Dose-dependent GI distress (vomiting, anorexia, diarrhea)
- Bone marrow depression (neutropenia, sepsis; nadir typically around day 10)
- Non-regenerative anemia
- Lethargy
- Seizures (specifically noted in cats)
- Blue-green discoloration of urine and sclera (benign)
- Tissue necrosis or phlebitis (if extravasated, though less severe than doxorubicin)
- Rarely: conjunctivitis, jaundice, renal failure, allergic reactions, thrombocytopenia
- Gastrointestinal signs (vomiting, anorexia, diarrhoea)
- Bone marrow depression (WBC nadir generally at 10 days)
- Seizure activity (reported in cats)
- Blue discoloration of urine and sclera (very rare)
- Acute renal failure (anecdotal in cats)
薬物相互作用
- Doxorubicin, Daunorubicin, or Radiation Therapy · Cardiotoxicity risks may be enhanced in patients that have previously received these therapies to the mediastinum.
- Immunosuppressant Drugs (e.g., azathioprine, cyclophosphamide, corticosteroids) · Concurrent use may significantly increase the risk of severe infection.
- Myelosuppressive Drugs (e.g., chloramphenicol, flucytosine, amphotericin B, colchicine) · Additive bone marrow depression; use with extreme caution.
- Live Vaccines · Increased risk of vaccine-induced infection; should be used with extreme caution or avoided during therapy.
- Myelosuppressive agents · Increased risk of severe bone marrow depression · major
- Immunosuppressive agents · Increased risk of severe immunosuppression and infection · major
- Heparin · Chemically incompatible · major
モニタリング
- CBC with differential and platelets (especially around day 7-10 to check for nadir)
- Tumor measurements/efficacy
- Chest radiographs, ECG, or other cardiac function tests (if cardiac symptomatology is present)
- Liver function tests (if jaundice or clinical signs of hepatotoxicity occur)
- Serum uric acid levels (for susceptible patients)
- Complete Blood Count (CBC), especially WBC count around day 10 post-administration
- Gastrointestinal signs (vomiting, diarrhoea, appetite)
- Renal parameters (especially in cats)
- Hepatic function
- Cardiac function (echocardiogram) if pre-existing disease exists
過量投与
Due to the narrow therapeutic index and potential for serious toxicity (profound myelosuppression, severe GI mucosal damage, sepsis), dosage determinations must be made with extreme care. Overdose management is primarily supportive, focusing on aggressive fluid therapy, broad-spectrum antibiotics to manage sepsis secondary to neutropenia, and potentially the use of recombinant granulocyte-colony stimulating factors (G-CSF) to accelerate bone marrow recovery.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。