雷尼替丁
**雷尼替丁 (Ranitidine)** 是一種競爭性組織胺H2受體拮抗劑和胃腸促動力藥，廣泛應用於獸醫學。 **主要臨床特徵：** * **抑制胃酸：** 用於治療和預防胃潰瘍、皺胃潰瘍、十二指腸潰瘍、尿毒症性胃炎，以及壓力或藥物引起的糜爛性胃炎。 * **促胃腸動力：** 在H2受體阻斷劑中較為獨特，雷尼替丁能刺激胃腸蠕動，適用於胃排空延遲及促進貓的結腸活動（例如巨結腸症）。 * **全身性肥大細胞增生症：** 幫助控制與肥大細胞瘤相關的胃酸分泌過多（肥大細胞瘤會釋放大量組織胺）。 > **臨床要點：** 雷尼替丁的效力（以莫耳濃度計）是西咪替丁 (Cimetidine) 的 3 到 13 倍。此外，由於它不會明顯抑制肝臟細胞色素 P450 酵素，因此藥物交互作用顯著較少，對於同時服用多種藥物的病患來說是更安全的選擇。
作用機制: 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.
各物種劑量
- 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)
給藥途徑
禁忌症
- Hypersensitivity to ranitidine
- No specific contraindications available in the monograph
不良反應
- 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)
藥物相互作用
- 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
監測
- 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
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.
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