呋喃妥因
**呋喃妥因 (Nitrofurantoin)** 是一種合成的呋喃類抗菌藥物，主要用作**泌尿道防腐劑/抗菌劑**。 * **部位特異性療效**：由於它會迅速排泄到尿液中，因此在下泌尿道能達到高濃度，但*無法*在全身血液循環或組織中達到治療濃度。因此，它對**下泌尿道感染 (UTIs)** 非常有效，但對全身性感染、腎盂腎炎（腎臟感染）或腎周圍膿腫**無效**。 * **抗菌譜**：對多種革蘭氏陰性菌和革蘭氏陽性菌有效，包括大腸桿菌 (*E. coli*)、克雷伯氏菌 (*Klebsiella*)、葡萄球菌 (*Staphylococcus*) 和腸球菌 (*Enterococcus*)。值得注意的是，它對假單胞菌 (*Pseudomonas* spp.) 和大多數變形桿菌 (*Proteus*) 無效。 * **臨床要點**：由於對第一線抗生素的抗藥性日益增加，呋喃妥因通常被保留用於治療多重抗藥性的下泌尿道感染，特別是由具抗藥性的大腸桿菌或腸球菌引起的感染。
作用機制: Nitrofurantoin can be bacteriostatic or bactericidal depending on the concentration and organism susceptibility. * **Mechanism**: Inside the bacterial cell, nitrofurantoin is reduced by bacterial **flavoproteins** to highly reactive intermediate compounds. * **Pathway**: Reactive intermediates → attack bacterial **ribosomal proteins** and other macromolecules → inhibit protein synthesis, aerobic energy metabolism (specifically **acetyl coenzyme A**), DNA synthesis, RNA synthesis, and cell wall synthesis. * **Environmental Factor**: It exhibits significantly greater antibacterial activity in **acidic environments**.
各物種劑量
- Susceptible bacterial urinary tract infections · 5 mg/kg · PO · q8h
- Recurrent UTI (Conventional dose) · 4 mg/kg · PO · q8h
- Recurrent UTI (Prophylactic dose) · 3-4 mg/kg · PO · q24h · Should be given at night after micturition and immediately before bedtime.
- Susceptible bacterial urinary tract infections · 4 mg/kg · PO · q6-8h
- Urinary tract infections (lower UTI only) · 4.4-5 mg/kg · PO · q8h · As directed by culture and sensitivity · For urinary tract infections only. Not for pyelonephritis.
- Susceptible urinary tract infections · 2.5-4.5 mg/kg · PO · q8h · Listed as three times daily.
- Susceptible urinary tract infections · 10 mg/kg · PO · q24h · Listed as daily.
- Prevention of re-infections with gram-negative organisms · 4 mg/kg · PO · q24h · Long-term · Give once a day immediately before bedtime after the dog has urinated. Only use after extensive search for underlying cause and after effective treatment of existing UTI.
- Recurrent UTI (Conventional dose) · 4 mg/kg · PO · q8h
- Recurrent UTI (Prophylactic dose) · 3-4 mg/kg · PO · q24h · Should be given at night after micturition and immediately before bedtime.
給藥途徑
禁忌症
- Renal impairment (decreased efficacy and increased risk of systemic toxicity)
- Known hypersensitivity to nitrofurantoin
- Pregnant patients at term (risk of hemolytic anemia in neonates)
- Neonates
- Rats (high risk of neurotoxicity)
- Significant renal impairment (decreased excretion leads to toxic serum levels)
- Pregnancy (mutagenic properties)
- Pyelonephritis
- Systemic infections outside the urinary tract
- Food-producing animals
不良反應
- Gastrointestinal disturbances (vomiting, nausea, diarrhea)
- Hepatopathy (can be severe or chronic)
- Myasthenic-like effects (rare, reversible in dogs)
- Infertility in male dogs
- Peripheral neuropathy (rare)
- Hemolytic anemia (rare)
- Pneumonitis (rare)
- Emesis
- Diarrhoea
- Gastrointestinal bleeding
- Hepatotoxicity
- Peripheral neuritis (rare)
- Pulmonary complications (rare)
- Thrombocytopenia (at high doses)
- Anaemia (at high doses)
- Leucopenia (at high doses)
藥物相互作用
- Fluoroquinolones (e.g., enrofloxacin, ciprofloxacin) · Nitrofurantoin may antagonize the antimicrobial activity of fluoroquinolones; concomitant use should be avoided.
- Food or Anticholinergic drugs · May increase the oral bioavailability and absorption of nitrofurantoin.
- Magnesium trisilicate containing antacids · May inhibit the oral absorption of nitrofurantoin.
- Probenecid · May inhibit the renal excretion of nitrofurantoin, potentially increasing systemic toxicity and reducing its effectiveness in the urinary tract.
- Antimuscarinic drugs · Delays gastric emptying time and increases absorption/bioavailability of nitrofurantoin · moderate
- Food · Delays gastric emptying time and increases absorption/bioavailability of nitrofurantoin · minor
- Fluoroquinolones · Antagonism of antibacterial efficacy · major
- Spironolactone · May increase the hyperkalaemic effects of spironolactone · moderate
- Urine alkalinizing agents · Significantly decreases the antibacterial activity of nitrofurantoin · major
監測
- Clinical efficacy (resolution of UTI symptoms, negative urine cultures)
- Adverse effects (especially GI upset)
- Periodic liver function tests (especially with chronic/prophylactic therapy)
- Resolution of clinical signs of UTI
- Urine culture and sensitivity
- Renal function (BUN, Creatinine)
- Complete Blood Count (CBC) if used long-term or at high doses
- Liver enzymes
過量
Because the drug is rapidly absorbed and excreted, patients with normal renal function usually require little therapy for mild overdoses. * **Massive Overdose**: If ingestion was recent, empty the gut using standard protocols (emesis/gastric lavage). * **Monitoring**: Monitor closely for gastrointestinal distress, hepatotoxicity, and neurologic signs. Provide supportive care as needed.
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。