イソトレチノイン
**イソトレチノイン**は、主に獣医皮膚科において、重度の角化異常症や皮脂腺異常の管理に使用される第一世代の合成レチノイドです。 **主な臨床応用：** * **犬の葉状魚鱗癬** * **皮膚T細胞リンパ腫**（上皮向性リンパ腫） * **皮内角化上皮腫** * **多発性表皮封入嚢胞** * **シュナウザーの面皰症候群** * **脂腺炎**（特にスタンダード・プードルやビズラ） * **猫のざ瘡（猫ニキビ）** > **臨床のポイント：** 皮脂腺に対する強力な作用があるため、イソトレチノインは脂腺炎やシュナウザー面皰症候群の第一選択レチノイドと見なされることが多く、原発性の角化異常には他のレチノイド（アシトレチンなど）が好まれる場合があります。 ヒトに対する重篤な催奇形性リスク（FDAカテゴリーX）があるため、獣医療用の本薬の入手はメーカーや販売業者によって厳しく制限される場合があります。
作用機序: Isotretinoin acts by regulating epithelial cell proliferation and differentiation. * **Receptor Binding:** Retinoids enter the cell and bind to intracellular **Retinoic Acid Receptors (RARs)** and **Retinoid X Receptors (RXRs)** → altering gene transcription. * **Sebosuppressive Effect:** It significantly reduces sebaceous gland size and activity → decreasing sebum production. * **Anti-keratinization & Anti-inflammatory:** Normalizes follicular desquamation (preventing comedone formation) and affects monocyte/lymphocyte function, altering cellular immune responses. * **Antimicrobial (Indirect):** By altering the microenvironment of the sebaceous pore (reducing sebum), it indirectly reduces bacterial populations.
動物種別の用量
- Feline acne · 5 mg/kg PO once daily · PO · q24h
- Feline acne · 10 mg per cat once daily PO · PO · q24h
- Feline acne · 1-3 mg/kg q12-24h PO · PO · q12-24h
- Epitheliotrophic lymphoma, cutaneus lymphoma · 10 mg/cat once daily PO · PO · q24h
- Sebaceous adenitis when more conservative treatments have failed · 1 mg/kg PO q12h for one month; if improvement is noted reduce dose to 1 mg/kg PO once daily; long-term goal is to treat with either 1 mg/kg PO every other day or 0.5 mg/kg once daily · PO · q12h initially, then q24h or q48h · Long-term
- Sebaceous adenitis · 1-3 mg/kg PO once a day to twice daily · PO · q12-24h
- Schnauzer comedo syndrome · 1 mg/kg once daily or divided q12h PO · PO · q12-24h
- Sebaceous adenitis in poodles; granulomatous sebaceous adenitis in viszlas · 1-2 mg/kg once daily or divided q12h PO · PO · q12-24h
- Epitheliotrophic lymphoma, cutaneus lymphoma · 2 mg/kg once daily or divided q12h PO · PO · q12-24h
- Schnauzer comedo syndrome, sebaceous adenitis in poodles, ichthyosis, keratocanthoma, epitheliotropic lymphoma, and sebaceous gland hyperplasia and adenoma · 1-3 mg/kg q12-24h PO · PO · q12-24h
投与経路
禁忌
- Pregnancy (absolute contraindication - known teratogen)
- Nursing mothers
- Hypertriglyceridemia
- Severe renal disease
- Severe hepatic disease
- Known hypersensitivity to isotretinoin
有害事象
- Dogs: Keratoconjunctivitis sicca (KCS) - most common
- Dogs: GI effects (anorexia, vomiting, diarrhea, abdominal distention)
- Dogs: CNS effects (lassitude, hyperactivity, behavioral changes, collapse)
- Dogs: Stiffness of limbs
- Dogs: Pruritus, exfoliative dermatitis, erythema of feet and mucocutaneous junctions/cheilitis
- Dogs: Polydipsia, swollen tongue
- Cats: Blepharospasm, periocular crusting, erythema
- Cats: Diarrhea
- Cats: Weight loss secondary to anorexia
薬物相互作用
- Vitamin A or other retinoids (etretinate, tretinoin) · May cause additive toxic effects.
- Cyclosporine · Isotretinoin may increase cyclosporine levels.
- Tetracyclines · Use with tetracyclines may increase the potential for the occurrence of pseudotumor cerebri (cerebral edema and increased CSF pressure).
モニタリング
- Clinical efficacy
- Liver function tests (baseline and if signs appear)
- Serum triglycerides and cholesterol
- Dogs: Schirmer Tear tests (monthly, especially in older dogs to monitor for KCS)
- Cats: Body weight (monitor for anorexia-induced weight loss)
過量投与
In a review of 147 exposures reported to the ASPCA APCC (140 dogs, 7 cats), only 5 dogs showed clinical signs, most commonly **hypersalivation**. Cats showed no clinical signs. Because of the drug's potential adverse effects, **gut emptying** should be considered with acute overdoses when warranted. Monitor for GI upset and CNS signs.
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。