ナイアシンアミド
ナイアシンアミド（ニコチンアミドとも呼ばれる）は、水溶性ビタミンB3のアミド型です。組織呼吸や脂質代謝に不可欠な栄養素として機能しますが、獣医薬理学における主な用途は**免疫調節薬**としてです。 犬の医療では、免疫介在性皮膚疾患を管理するために、**テトラサイクリン**（またはドキシサイクリン）との相乗的な組み合わせで処方されることが最も一般的です。特に**円板状エリテマトーデス（DLE）**や**紅斑性天疱瘡**に有効であり、罹患犬の25％〜65％で有効性を示します。 > **臨床のポイント：** ナイアシンアミドとナイアシン（ニコチン酸）を区別することが重要です。ナイアシンとは異なり、ナイアシンアミドは皮膚の血管拡張（「ナイアシンフラッシュ」）を引き起こさず、血中脂質レベルや心血管系に影響を与えないため、犬の長期的な免疫調節において安全で適切な選択肢となります。
作用機序: At pharmacologic doses, niacinamide exerts anti-inflammatory and immunomodulatory effects through several pathways: * **Mast Cell Stabilization:** Blocks **IgE-induced histamine release** and prevents the degranulation of mast cells. * **Enzyme Inhibition:** Inhibits **phosphodiesterase (PDE)** enzymes → increases intracellular cAMP → decreases the release of inflammatory proteases. * **Synergy with Tetracyclines:** When used concurrently with tetracycline or doxycycline, the combination suppresses leukocyte chemotaxis that occurs secondary to complement activation by antibody-antigen complexes. * **Nutritional Role:** Acts as a precursor to NAD and NADP, essential coenzymes for tissue respiration, glycogenolysis, and lipid metabolism.
動物種別の用量
- Discoid lupus erythematosus · For dogs weighing 10 kg or more: 500 mg of niacinamide and 500 mg of tetracycline PO q8h. For dogs weighing from 5-10 kg: 250 mg of each drug PO q8h. For dogs weighing less than 5 kg: 100 mg of each drug PO q8h. · PO · q8h · Improvement usually noted within 6 weeks · Given in combination with tetracycline.
- Discoid lupus erythematosus or pemphigus · Dogs weighing more than 10 kg: 500 mg of niacinamide and 500 mg of tetracycline PO q8h. For dogs weighing less than 10 kg: 250 mg of each PO q8h. · PO · q8h · May use in combination with corticosteroids and Vitamin E. If adverse effects become a problem, reduce dose of niacinamide first.
- Various immune-mediated diseases (DLE, pemphigus, vasculitis, dermatomyositis, etc.) · For dogs less than 10 kg: 250 mg each of niacinamide and tetracycline PO three times daily. For dogs larger than 10 kg: 500 mg each of niacinamide and tetracycline PO three times daily. · PO · TID · May substitute doxycycline for tetracycline at 5 mg/kg PO once a day.
- Pemphigus foliaceous · Doses as above (with prednisone and azathioprine). Once remission has occurred the dose may be gradually tapered to once daily administration. · PO · TID initially, taper to q24h · Improvement within 1-2 months · Used as adjunctive therapy.
- Adjunctive therapy for pemphigus or discoid lupus erythematosus · 100 mg of each for dogs <5kg; 250 mg of each for dogs 5-10 kg; 500 mg of each for dogs >10 kg PO three times daily until resolve (90-120 days), then decrease by one dose per day per month (three times daily to two times daily to once daily and eventually to every other day for 30-60 days.) · PO · TID initially, then tapered · 90-120 days initially, then 30-60 days taper · Given with tetracycline.
- Immunomodulation (e.g., lupoid onychodystrophy, discoid lupus erythematosus, pemphigus foliaceus) · 250 mg/dog (dogs up to 25 kg), 500 mg/dog (dogs >25 kg) · PO · q8h · Taper to effect · Often used in combination with oxytetracycline, tetracycline, or doxycycline.
投与経路
禁忌
- Liver disease
- Active peptic ulcers
- Hypersensitivity to niacinamide
- Do not use nicotinic acid (niacin) as a substitute due to severe vasodilation (flushing) effects.
有害事象
- Anorexia
- Vomiting
- Lethargy
- Elevated liver enzymes (occasional)
- Increased seizure frequency (anecdotal)
- Mild gastrointestinal irritation (anorexia, vomiting, diarrhea)
薬物相互作用
- Insulin · May require dosage adjustments after initiating niacinamide therapy due to potential alterations in glycemic control.
- Oral Antidiabetic Agents · May require dosage adjustments after initiating niacinamide therapy.
モニタリング
- Clinical efficacy (resolution of dermatologic lesions)
- Adverse effects (GI upset, lethargy)
- Liver enzymes (baseline and occasional monitoring suggested)
- Clinical resolution of dermatological lesions
- Gastrointestinal signs (vomiting, diarrhea, anorexia)
- Liver enzymes (if used long-term or at high doses)
過量投与
Acute toxicity is rare. Overdoses are unlikely to cause significant problems other than acute gastrointestinal distress (vomiting, diarrhea).
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。