ファモチジン
Famotidine
3-[({2-[(diaminomethylidene)amino]-1,3-thiazol-4-yl}methyl)sulfanyl]-N'-sulfamoylpropanimidamide
別名: Pepcid AC · Pepcid RPD · famotidinum · L-643341 · MK-208 · YM-11170 · Famotidina
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 |
|---|---|---|---|---|---|
| To reduce gastric acid production | 0.1-0.2 mg/kg | PO, SC, IM, IV | q12h | — | 🌎 NA |
| To reduce gastric acid production | 0.5 mg/kg | PO, SC, IM, IV | q12-24h | — | 🌎 NA |
| For esophagitis | 0.5-1 mg/kg | PO | q12h | — | 🌎 NA |
| For acute reflex esophagitis | 0.55-1.1 mg/kg | PO | q24h (or q12h if severe) | 2-3 weeks | 🌎 NA |
| Adjunctive treatment (prevent/treat gastric ulcers) of mast cell tumors | 0.5 mg/kg | Not specified | q24h | — | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic kidney disease | 0.5 mg/kg | PO | q24h | — | 🌎 NA |
| All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions) | 0.5-1.0 mg/kg | PO | q12-24h | — | 🌍 EU |
- Adjunctive treatment of GI effects associated with chronic kidney disease: Effective evidence grade: 3
- All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions): Effect on gastric pH diminishes with time when given daily.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| To reduce gastric acid production | 0.2 mg/kg | PO, SC, IM, IV | q24h | — | 🌎 NA |
| To reduce gastric acid production | 0.5 mg/kg | PO, SC, IM, IV | q12-24h | — | 🌎 NA |
| For esophagitis | 0.5 mg/kg | PO | q12h | — | 🌎 NA |
| For acute reflex esophagitis | 0.55-1.1 mg/kg | PO | q24h (or q12h if severe) | 2-3 weeks | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic progressive renal disease | 1 mg/kg | PO | q24h | — | 🌎 NA |
| Adjunctive treatment of GI effects associated with chronic progressive renal disease | 0.5-1 mg/kg | PO | q12-24h | — | 🌎 NA |
| All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions) | 0.5-1.0 mg/kg | PO | q12-24h | — | 🌍 EU |
- To reduce gastric acid production: See warning about IV use in cats
- All uses (ulcers, gastritis, oesophagitis, hypersecretory conditions): Effect on gastric pH diminishes with time when given daily.
小型哺乳類
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Rabbits: For stress induced ulcer prevention once critically ill animal has stabilized | 1 mg/kg | IV | q24h | — | 🌎 NA |
フェレット
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| For stress induced ulcers | 0.25-0.5 mg/kg | PO, IV | q24h | — | 🌎 NA |
| In combination with antibiotics for Helicobacter treatment | 0.25-0.5 mg/kg | PO, IV | q24h | — | 🌎 NA |
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| As an adjunct in ulcer treatment | 0.23 mg/kg or 0.35 mg/kg | IV | q8h (for 0.23 mg/kg) or q12h (for 0.35 mg/kg) | — | 🌎 NA |
| As an adjunct in ulcer treatment | 1.88 mg/kg or 2.8 mg/kg | PO | q8h (for 1.88 mg/kg) or q12h (for 2.8 mg/kg) | — | 🌎 NA |
- As an adjunct in ulcer treatment: ARCI UCGFS Class 5 Drug
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
ファモチジンは強力で長時間作用型のヒスタミンH2受容体拮抗薬であり、獣医学において胃酸分泌を抑制し、胃・十二指腸潰瘍、胃炎、食道炎の治療または予防に広く使用されています。
シメチジンと比較して、ファモチジンは著しく強力であり、投与頻度が少なくて済みます。さらに重要なことに、肝臓のシトクロムP450酵素系を阻害しないため、多くの一般的な薬物相互作用を回避できます。
臨床のポイント: 軽度の胃酸抑制や日常的な予防には有効ですが、活動性潰瘍の治療、運動誘発性胃炎の予防、または重度の食道炎の管理には、オメプラゾールなどのプロトンポンプ阻害薬（PPI）が一般的に優れているとされています。さらに、犬や猫に3〜14日間連続して使用すると、薬理学的な耐性（タキフィラキシー）が生じやすく、時間の経過とともに胃酸抑制効果が減弱する傾向があります。
作用機序
Famotidine acts as a competitive, reversible antagonist at the H2 receptors located on the basolateral membrane of gastric parietal cells.
By blocking histamine binding, it prevents the activation of adenylate cyclase → decreases intracellular cAMP levels → reduces the activation of the H+/K+-ATPase proton pump. This effectively blunts both basal gastric acid secretion and secretion stimulated by food, pentagastrin, or insulin. By decreasing the total volume of gastric juice produced, H2-blockers also indirectly decrease the amount of pepsin secreted. It does not alter gastric emptying time, biliary secretion, or lower esophageal sphincter pressure.
安全性・警告
禁忌
- Known hypersensitivity to H2 blockers
- Known hypersensitivity to famotidine or other H2 receptor antagonists
有害事象
- Bradycardia (if infused too rapidly IV)
- GI effects (anorexia, vomiting, diarrhea)
- Headache
- Dry mouth or skin
- Intravascular hemolysis (rare, anecdotally reported in cats given IV)
- Transient increase in serum gastrin (returns to baseline by 14 days)
- Generally has a very good safety profile with fewer side effects than cimetidine
注意事項
Use cautiously in geriatric patients and those with significantly impaired hepatic or renal function; consider dosage reduction in patients with significant renal dysfunction. Famotidine may have negative inotropic effects and some cardioarrhythmogenic properties; use with caution in patients with cardiac disease. When administering IV to cats, infuse slowly (over 5 minutes) to minimize the rare risk of intravascular hemolysis.
医薬品相互作用
Famotidine raises gastric pH, which may decrease the absorption of these agents. Administer the azole one hour prior to famotidine.
Famotidine may decrease the absorption of these cephalosporins. Taking with food may alleviate this effect.
Famotidine may decrease the absorption of oral iron. Administer iron at least one hour prior to famotidine.
監視
- Clinical efficacy (decrease in symptomatology, endoscopic examination, resolution of blood in feces)
- Adverse effects
- Clinical signs of GI ulceration or bleeding (vomiting, melena, anorexia)
- Gastric pH (if clinically indicated and feasible)
薬物動態
半減期
吸収
Incompletely absorbed after oral administration with minimal first-pass metabolism. Systemic bioavailability is ~40-50% in humans. Bioavailability is low in horses (13%).
分布
Concentrates in the liver, pancreas, kidney, and submandibular gland (in rats). Only ~15-20% is bound to plasma proteins. Does not cross the blood-brain barrier or placenta in rats. Distributed into milk. Volume of distribution in horses is 4.28 L/kg.
代謝
Primarily metabolized in the liver.
消失
Excreted in the urine. After oral dosing, ~1/3 is excreted unchanged; after IV dosing, ~2/3 is excreted unchanged.
過剰投与
Famotidine has a wide margin of safety. The minimum acute lethal dose in dogs is reported to be >2 grams/kg for oral doses and approximately 300 mg/kg for intravenous doses.
IV doses in dogs ranging from 5-200 mg/kg caused vomiting, restlessness, mucous membrane pallor, and redness of the mouth and ears. Higher doses caused hypotension, tachycardia, and collapse.
Most overdoses require only monitoring. In massive oral overdoses, gut-emptying protocols should be considered and supportive therapy initiated when warranted.
製品
製剤
- Oral tablets (plain, film-coated, chewable, orally disintegrating)
- Powder for oral suspension
- Injection
- 20 mg tablets
- 40 mg tablets
ヒト用医薬品
- Famotidine Oral Tablets (plain, film-coated, chewable & orally disintegrating) & Gelcaps: 10 mg, 20 mg, & 40 mg (Pepcid®, Pepcid AC®, generic)
- Famotidine Powder for Oral Suspension: 8 mg/mL when reconstituted (Pepcid®)
- Famotidine Injection: 10 mg/mL in vials; 20 mg/50 mL premixed containers (generic)
- 20 mg tablets
- 40 mg tablets
規制ステータス
Human authorized product used off-label under the cascade. Cimetidine is the only H2 antagonist with veterinary authorization.
Human authorized product used off-label under the cascade (POM).
規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Tablets should be stored in well-closed, light-resistant containers at room temperature. Powder for oral suspension should be stored <40°C; after reconstitution, it is stable for 30 days when stored <30°C (do not freeze). Injection should be stored in the refrigerator (2-8°C).
飼主向け情報
- 投与方法: 獣医師の指示通りに正確に投与してください。胃酸抑制効果を最大にするため、通常は空腹時（食事の30〜60分前）に投与するのが最適です。
- 継続的な投与: 投与を忘れないでください。投与を忘れると、胃酸逆流や潰瘍の臨床症状が再発する可能性があります。
- 液体製剤: 調剤された経口懸濁液を使用する場合は、使用前によく振り、冷蔵庫で保管してください。30日経過して残った分は廃棄してください。
- 相互作用: ペットが他の薬やサプリメントを服用している場合は、獣医師に知らせてください。経口鉄剤や特定の抗真菌薬を服用している場合は、ファモチジンと少なくとも1時間の間隔を空けて投与する必要があります。
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