阿斯匹靈
**阿斯匹靈 (乙醯水楊酸)** 是一種經典的非類固醇消炎止痛藥 (NSAID)，廣泛應用於多種獸醫物種，具有鎮痛、解熱和抗發炎的特性。 除了疼痛管理外，阿斯匹靈在獸醫學中的獨特價值在於其**抗血小板作用**。它常被用作狗（例如：免疫介導性溶血性貧血、心絲蟲病或腎小球疾病）和貓（例如：預防繼發於肥厚型心肌病的動脈血栓栓塞）的抗血栓藥物。 > **臨床要點：** 貓咪使用阿斯匹靈必須極度謹慎。貓科動物體內缺乏代謝水楊酸所需的**葡萄糖醛酸轉移酶 (glucuronyl transferase)**。這導致藥物半衰期大幅延長（貓可達 45 小時，而狗僅約 8 小時），如果給藥過於頻繁，極易造成致命的藥物蓄積和中毒。
作用機制: Aspirin exerts its effects primarily through the **irreversible inhibition of cyclooxygenase (COX) enzymes**, with a strong affinity for **COX-1**. - **Anti-inflammatory & Analgesic:** Inhibits COX-1 (and to a lesser extent COX-2) → decreases synthesis of pro-inflammatory **prostaglandins**. - **Antiplatelet Effect:** Irreversibly acetylates COX-1 in platelets → blocks the synthesis of **Thromboxane A2 (TXA2)**, a potent inducer of platelet aggregation and vasoconstriction. Because platelets lack a nucleus, they cannot synthesize new COX enzymes; thus, the antiplatelet effect lasts for the lifespan of the platelet (typically 7-10 days). - **Gastric Protection Modulator:** While aspirin does not directly inhibit COX-2, it modifies it to interact with lipoxygenase (LOX) → produces **aspirin-triggered lipoxin (ATL)**, which provides some gastric mucosal protective actions, potentially explaining why gastric damage may decrease with chronic use.
各物種劑量
- For analgesia · 10 mg/kg PO q12h · PO · q12h · Recommend using buffered varieties of aspirin in dogs.
- As an antiinflammatory/antirheumatic · 25 mg/kg PO q8h · PO · q8h
- For antipyrexia · 10 mg/kg PO twice daily · PO · twice daily
- Post-Adulticide therapy for heartworm disease · 7-10 mg/kg PO once a day · PO · once a day
- For adjunctive therapy in IMHA (antithrombotic) · 0.5 mg/kg PO twice daily · PO · twice daily · At this low dose risk for gastric ulceration is low, but adding misoprostol may reduce the risk.
- For adjunctive therapy of glomerular disease (antithrombotic) · 0.5 mg/kg PO q24h · PO · q24h
- For adjunctive therapy with azathioprine and glucocorticoids for immune-mediated hemolytic anemia · 0.5 mg/kg PO once daily · PO · once daily
- As an analgesic/antiinflammatory prior to elective intraocular surgery · 6.5 mg/kg two to three times daily · PO · two to three times daily
- Reduction of platelet aggregation (e.g. IMHA) · 0.5-1 mg/kg · PO · q24h · Alternatively 0.5 mg/kg p.o. q12h. Doses are anecdotal.
- Analgesia, pyrexia, inflammation · 10-20 mg/kg · PO · q12h · Safety and efficacy of this dose has not been established.
給藥途徑
禁忌症
- Known hypersensitivity to salicylates
- Active gastrointestinal bleeding or ulcers
- Bleeding disorders (relative contraindication)
- Asthma (relative contraindication)
- Renal insufficiency (relative contraindication)
- Pregnancy (especially later stages; low-grade teratogen and may delay labor)
不良反應
- Gastric irritation (nausea, anorexia, vomiting)
- Gastrointestinal ulceration and occult blood loss
- Secondary anemia or hypoproteinemia (due to chronic GI blood loss)
- Metabolic acidosis (especially in cats)
- Hypersensitivity reactions (rare in dogs)
藥物相互作用
- Alkalinizing drugs (e.g., sodium bicarbonate, acetazolamide) · Significantly increases the renal excretion of salicylates; carbonic anhydrase inhibitors may cause systemic acidosis and increase CNS salicylate levels, leading to toxicity.
- Aminoglycosides · May increase the likelihood of nephrotoxicity. · major
- Corticosteroids · May increase salicylate clearance (decreasing serum levels) and significantly increase the risk of gastrointestinal ulceration and bleeding.
- Digoxin · Aspirin may increase plasma levels of digoxin by decreasing its clearance.
- Furosemide · May compete with renal excretion of aspirin, delaying its elimination and potentially causing toxicity at high doses.
- Heparin or Oral Anticoagulants · Increased risk of bleeding due to synergistic antiplatelet/anticoagulant effects.
- Methotrexate · Aspirin may displace methotrexate from plasma proteins, increasing the risk of methotrexate toxicity.
- Other NSAIDs · Increased risk of severe GI ulceration. A washout period of 3-10 days is recommended when switching from aspirin to a COX-2 selective NSAID. · major
- Phenobarbital · May increase the rate of aspirin metabolism by inducing hepatic enzymes.
- Probenecid, Sulfinpyrazone · Aspirin may antagonize the uricosuric effects of these drugs.
- Spironolactone · Aspirin may inhibit the diuretic activity of spironolactone.
監測
- Analgesic and/or antipyretic efficacy
- Bleeding times (if indicated)
- Packed Cell Volume (PCV)
- Stool guaiac tests (for occult GI bleeding)
- Acid-base status (in cases of overdose)
過量
**Clinical Signs of Acute Toxicity:** - **Early signs:** Depression, vomiting (may be blood-tinged), anorexia, hyperthermia, panting/increased respiratory rate. - **Acid-Base Disturbances:** Initially, a respiratory alkalosis occurs due to hyperventilation, followed by a profound metabolic acidosis. - **Severe signs:** Muscular weakness, pulmonary and cerebral edema, hypernatremia, hypokalemia, ataxia, seizures, coma, and death. **Treatment Protocol:** 1. **Decontamination:** Emesis (if within 12 hours of ingestion), activated charcoal, and an oral cathartic. Gastric lavage with 3-5% sodium bicarbonate may delay absorption. 2. **Fluid Therapy:** IV fluids (e.g., Dextrose 5% in water) to correct dehydration. 3. **Alkaline Diuresis:** Forced alkaline diuresis with sodium bicarbonate enhances renal excretion, but should only be attempted if acid-base status can be monitored. Mannitol (1-2 g/kg/hr) may enhance diuresis. 4. **Supportive Care:** GI protectants. Control seizures with IV diazepam. 5. **Coagulopathy Management:** Phytonadione (Vitamin K1) at 2.5 mg/kg divided q8-12h and ascorbic acid (though ascorbic acid may negate urinary alkalinization). 6. **Heroic Measures:** Peritoneal dialysis or exchange transfusions in severe cases.
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