Methionine
**Methionine** is a sulfur-containing essential amino acid used primarily in veterinary medicine as a **urinary acidifier** and nutritional supplement. * **Urinary Acidification:** Historically used to dissolve and prevent **struvite (magnesium ammonium phosphate) uroliths** by lowering urine pH. * **Clinical Pearl:** Its use in small animals has largely been superseded by specialized prescription urinary diets (e.g., s/d, c/d) that effectively manage urine pH without the need for additional supplementation. * **Lipotropic Agent:** Acts as a lipotrope to prevent or correct fatty liver in choline-deficient states. * **Large Animal Use:** Used as a nutritional supplement in swine and poultry, for the treatment of ketosis in cattle, and purportedly for laminitis in horses and cattle (theorized to provide a disulfide bond substrate to maintain the hoof-pedal bone bond), though definitive efficacy for laminitis is lacking.
กลไกการออกฤทธิ์: Methionine exerts its effects through several metabolic pathways: * **Urine Acidification:** Methionine is metabolized in the liver, where its sulfur component is oxidized to **sulfate**. This sulfate is excreted by the kidneys as **sulfuric acid** → effectively lowering urine pH. * **Lipotropic Action:** Methionine supplies methyl groups to **ethanolamine** → forms **choline**, which is essential for lipid transport and metabolism in the liver, preventing hepatic lipidosis. * **Antioxidant & Structural Precursor:** Two molecules of methionine convert to one molecule of **cysteine**, a critical precursor for **glutathione** (a major endogenous antioxidant) and essential for disulfide bond formation in structural proteins (like keratin in hooves).
ขนาดยาตามชนิดสัตว์
- Urine acidification · 1000-1500 mg per day given in the food once daily · PO · q24h · Use if diet and antimicrobials do not reduce pH.
- Urine acidification · 0.2-1 gram PO once daily · PO · q24h
- General / Ketosis · 20-30 grams PO · PO
- Laminitis (purported) · 22 mg/kg PO once daily for one week; then 11 mg/kg PO once daily for 1 week; then 5.5 mg/kg PO once daily for one week · PO · q24h · 3 weeks
- Senecio-induced liver damage · 12.5 grams IV in one liter saline/dextrose solution · IV · Once
- Urine acidification (struvite dissolution) · 100 mg/kg PO q12h · PO · q12h · Safe and effective in dissolving presumed infection-induced struvite uroliths in combination with an appropriate anti-microbial agent without using a struvite dissolution diet.
- Struvite dissolution therapy (if diet and antimicrobials do not result in acid urine) · 0.2-1 gram PO q8h · PO · q8h
ขนาดยาเป็นข้อมูลอ้างอิงทางคลินิกสำหรับสัตวแพทย์ผู้มีใบอนุญาต โปรดตรวจสอบกับฉลากล่าสุดและผู้ป่วยแต่ละรายเสมอ
วิธีการให้ยา
ข้อห้ามใช้
- Renal failure
- Pancreatic disease
- Hepatic insufficiency
- Preexisting acidosis
- Oxalate or urate calculi
- Kittens
- Pre-existing metabolic acidosis
- Severe liver disease or hepatic encephalopathy
- Urate, cystine, or calcium oxalate urolithiasis
- Young growing animals
- Pregnant or nursing animals
อาการไม่พึงประสงค์
- Gastrointestinal distress (nausea, vomiting)
- Heinz-body hemolytic anemia (especially in cats)
- Methemoglobinemia
- Ataxia
- Cyanosis
- Metabolic acidosis
- Gastrointestinal upset (nausea, vomiting, diarrhea)
- Heinz body anemia (especially in cats at high doses)
- Worsening of hepatic encephalopathy in patients with liver disease
อันตรกิริยาระหว่างยา
- Aminoglycosides (gentamicin, amikacin) · Urine acidification may diminish the effectiveness of aminoglycosides in treating bacterial urinary tract infections, as they are more effective in an alkaline medium.
- Erythromycin · Urine acidification may diminish the effectiveness of erythromycin in treating bacterial urinary tract infections.
- Quinidine · Urine acidification may increase the renal excretion of quinidine, potentially lowering its systemic levels.
- Other urinary acidifiers (e.g., ammonium chloride) · Additive acidification leading to severe metabolic acidosis · major
- Urinary acidifying diets · Excessive lowering of urine pH and increased risk of metabolic acidosis · major
การติดตาม
- Urine pH (goal of therapy is typically ≤6.5)
- Blood pH (if signs of toxicity or metabolic acidosis are present)
- CBC in cats (if exhibiting signs of toxicity, to check for Heinz-body anemia)
- Urine pH
- Complete Blood Count (CBC) to monitor for Heinz bodies, especially in cats
- Acid-base status (blood gases) if overdosage is suspected
- Liver function
การได้รับยาเกินขนาด
**Feline Toxicity:** Cats are particularly sensitive to methionine overdose. * When administered at a dose of 2 grams orally per day to mature cats, it caused **anorexia, methemoglobinemia, Heinz body formation (with resultant hemolytic anemia), ataxia, and cyanosis**. * **Kittens:** Methionine may be highly toxic to kittens who consume other cats' food to which methionine has been added. **General Toxicity:** Metabolic acidosis can occur with overdoses in any species, particularly when used in combination with an acidifying diet. No specific information was located on the treatment of methionine overdosage; treatment should be symptomatic and supportive (e.g., correcting acid-base imbalances).
ข้อมูลอ้างอิงยาของ VetSheet มีไว้สำหรับสัตวแพทย์ผู้มีใบอนุญาตเพื่อช่วยในการตัดสินใจทางคลินิก ไม่ใช่สิ่งทดแทนการวินิจฉัยของผู้เชี่ยวชาญหรือฉลากล่าสุดของผู้ผลิต