馬尿酸烏洛托品
**馬尿酸烏洛托品**是一種泌尿道防腐劑，主要用於預防反覆發作的泌尿道感染 (UTIs)。 * **臨床應用：** 在獸醫學中不常作為第一線藥物，且在犬貓的療效證據有限。通常保留用於傳統抗生素治療無效或有禁忌症的具抗藥性、反覆性下泌尿道感染。 * **機制依賴性：** 其療效嚴格依賴於酸性尿液環境（pH 值 < 6.5，理想情況下 < 5.5）。在鹼性尿液中，該藥物不具活性。 * **抗菌譜：** 活化後，它對革蘭氏陽性菌（*葡萄球菌*、*腸球菌*）和革蘭氏陰性菌（*大腸桿菌*、*假單胞菌*、*變形桿菌*）提供廣效、非特異性的殺菌活性，據報導對某些真菌病原體也有效。 * **臨床要點：** 由於它會轉化為甲醛，細菌不會對其產生質體介導或染色體抗藥性，這使其在慢性預防中具有獨特的價值。
作用機制: Methenamine is a prodrug that requires an acidic environment for activation. * **Hydrolysis Pathway:** In an acidic urinary environment (pH < 6.5) → **methenamine** is hydrolyzed → **formaldehyde** + **ammonia**. * **Bactericidal Action:** **Formaldehyde** acts as a non-specific bactericidal agent by denaturing bacterial proteins and nucleic acids. * **Role of Hippurate:** The **hippuric acid** salt component serves a dual purpose: it acts as a weak acid to help lower the urinary pH (facilitating the conversion to formaldehyde) and possesses mild, non-specific antibacterial activity of its own. * **Systemic Inactivity:** At physiological blood pH (7.4), methenamine remains stable and inactive, ensuring that formaldehyde is only generated locally within the urinary bladder.
各物種劑量
- Urinary tract infection prophylaxis · 250 mg · PO · q12h · Methenamine hippurate
- Urinary tract infection prophylaxis · 10 mg/kg · PO · q6h · Methenamine mandelate; use with ammonium chloride to acidify urine and increase effectiveness
- Urinary tract infection prophylaxis · 10 mg/kg · PO · q6h · Methenamine mandelate
- Urinary tract infection prophylaxis · 10-20 mg/kg · PO · q8-12h · Methenamine mandelate; urine pH may need to be lowered by use of an acidifying diet and/or urinary acidifiers
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Hypersensitivity to methenamine or its salts
- Renal insufficiency
- Metabolic acidosis
- Severe hepatic impairment (due to ammonia production during hydrolysis)
- Severe dehydration
不良反應
- Gastrointestinal irritation (nausea, vomiting, anorexia)
- Dysuria (secondary to formaldehyde irritation with long-term use)
- Systemic acidosis (potential)
- Lipoid pneumonitis (reported in humans using oral suspension)
藥物相互作用
- Sulfamethiazole · Not recommended; an insoluble precipitate may form in the urine.
- Urine Alkalinizing Drugs (e.g., calcium/magnesium antacids, carbonic anhydrase inhibitors, citrates, sodium bicarbonate, thiazide diuretics) · May reduce the efficacy of methenamine by preventing its conversion to formaldehyde in the urine.
監測
- Urine pH (must remain < 6.5)
- Clinical efficacy (resolution or prevention of UTI symptoms)
- Urinalysis and urine cultures
過量
Dogs have tolerated single IV dosages of up to 600 mg/kg of methenamine hippurate without overt toxic effects. **Management of Large Oral Overdoses:** * Implement established gut emptying protocols (emesis/gastric lavage) if ingestion is recent. * Maintain hydration status with intravenous fluids. * Provide symptomatic and supportive care as required, monitoring for systemic acidosis and gastrointestinal distress.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。