ラニチジン
**ラニチジン（Ranitidine）**は、獣医療で広く使用されている競合的ヒスタミンH2受容体拮抗薬および消化管運動促進薬です。 **主な臨床的特徴：** * **胃酸分泌抑制：** 胃潰瘍、第四胃潰瘍、十二指腸潰瘍、尿毒症性胃炎、およびストレスや薬物誘発性のびらん性胃炎の治療と予防に使用されます。 * **消化管運動促進作用：** H2ブロッカーの中ではユニークなことに、ラニチジンは消化管運動を刺激するため、胃排出遅延や猫の結腸活動の促進（巨大結腸症など）に有用です。 * **全身性肥満細胞症：** 肥満細胞腫（大量のヒスタミンを放出する）に関連する胃酸過分泌状態の管理に役立ちます。 > **臨床のポイント：** ラニチジンはシメチジンと比較してモルベースで3〜13倍強力です。さらに、肝臓のシトクロムP450酵素をほとんど阻害しないため、薬物相互作用が著しく少なく、複数の薬剤を服用している患者にとってより安全な選択肢となります。
作用機序: Ranitidine exerts its effects via two distinct mechanisms: 1. **Gastric Acid Suppression:** It competitively inhibits **histamine** at the **H2 receptors** located on the basolateral membrane of gastric parietal cells. * Histamine blockade → decreased intracellular cAMP → reduced activation of the **H+/K+ ATPase (proton pump)** → significant reduction in both basal and stimulated gastric acid and pepsin secretion. 2. **Prokinetic Effect:** It reversibly inhibits **acetylcholinesterase (AChE)** in the gastrointestinal tract. * AChE inhibition → decreased breakdown of acetylcholine → increased **acetylcholine (ACh)** at muscarinic receptors → stimulation of GI smooth muscle motility and increased lower esophageal sphincter pressure.
動物種別の用量
- For ulcer disease/esophagitis · 2.5 mg/kg IV q12h or 3.5 mg/kg PO q12h · IV, PO · q12h
- For ulcer disease/esophagitis · 1-2 mg/kg · PO, IV, SC · q12h
- For ulcer disease/esophagitis · 2 mg/kg · PO, IV · q12h
- As a prokinetic agent to stimulate colonic motility · 1-2 mg/kg · PO · q8-12h
- As a prokinetic agent to stimulate colonic motility · 1-2 mg/kg · PO · q12h
- All uses · 2 mg/kg/day · IV · constant infusion · Not an effective acid suppressant in healthy cats.
- All uses · 2.5 mg/kg · IV · Not specified · Not an effective acid suppressant in healthy cats.
- For Helicobacter mustelae · 24 mg/kg · PO · q8-12h · 14 days · Uses Ranitidine bismuth citrate (must be compounded). Given with clarithromycin (12.5 mg/kg PO q8-12h).
- Foals · 1.5 mg/kg IV q8h or 6.6 mg/kg PO q8h · IV, PO · q8h · Often used with omeprazole (4 mg/kg PO q24h).
- Foals · 6.6 mg/kg IV q4h or 0.8-2.2 mg/kg IV four times a day; 5-10 mg/kg PO two to four times a day. · IV, PO · q4h or QID (IV); BID-QID (PO)
投与経路
禁忌
- Hypersensitivity to ranitidine
- No specific contraindications available in the monograph
有害事象
- Vomiting (associated with rapid IV boluses in small animals)
- Pain at the injection site (IM administration)
- Mental confusion (rare, documented in humans)
- Headache (rare, documented in humans)
- Agranulocytosis (rare)
- Transient cardiac arrhythmias (if given too rapidly IV)
- Cardiac arrhythmias (rare, typically with rapid IV)
- Hypotension (rare, typically with rapid IV)
薬物相互作用
- Acetaminophen · Ranitidine (dose-dependent) may inhibit acetaminophen metabolism.
- Antacids · High doses may decrease the absorption of ranitidine; administer at least 2 hours apart. · moderate
- Ketoconazole · Absorption of ketoconazole may be reduced secondary to increased gastric pH.
- Itraconazole · Absorption of itraconazole may be reduced secondary to increased gastric pH.
- Metoprolol · Ranitidine may increase metoprolol half-life and peak serum levels.
- Nifedipine · Ranitidine may increase nifedipine AUC by 30%.
- Propantheline · Delays the absorption but increases the peak serum level of ranitidine; relative bioavailability may be increased by 23%.
- Vitamin B-12 · Long-term ranitidine use may reduce oral absorption of Vitamin B-12.
- Sucralfate · May affect absorption; advisable to administer sucralfate 2 hours before H2 blockers · minor
- Digoxin · Ranitidine may reduce absorption or effect; stagger oral doses by 2 hours · moderate
- Metoclopramide · Ranitidine may reduce absorption or effect; stagger oral doses by 2 hours · moderate
モニタリング
- Clinical efficacy (resolution of clinical signs, improved appetite, absence of blood in feces/vomitus)
- Endoscopic examination (if indicated for ulcer healing)
- Serum ALT values (consider monitoring during high-dose, chronic IV therapy)
- Resolution of gastrointestinal clinical signs
- Heart rate and blood pressure (during IV administration)
過量投与
Clinical experience with ranitidine overdosage is limited, but the drug has a wide margin of safety. * **Signs of Toxicity:** In laboratory animals, massive doses (225 mg/kg/day) have caused muscular tremors, vomiting, and rapid respirations. Single doses of 1 gram/kg in rodents were not fatal. * **Treatment:** Handle using standard protocols for oral drug ingestions (e.g., gastric decontamination if recent and appropriate). Treat clinical signs symptomatically and supportively. Hemodialysis and peritoneal dialysis can effectively remove ranitidine from the body.
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。