Nitrofurantoin
Nitrofurantoin is a nitrofuran antibacterial used principally for susceptible lower urinary tract infections. Renal excretion concentrates active drug in urine, while systemic tissue exposure is comparatively low. Veterinary applications mainly involve selected dogs with bacterial cystitis, including some infections caused by organisms resistant to more commonly used urinary antibacterials.
Group
Urinary antibacterial
Mechanism of Action
Bacterial nitroreductases convert nitrofurantoin to reactive intermediates that damage multiple cellular targets. Effects on ribosomal proteins, enzymes and nucleic-acid pathways disrupt bacterial function and produce antimicrobial activity. Useful exposure is concentrated in urine after renal elimination. This combination of activation and distribution explains its role as a lower urinary tract antibacterial.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lower urinary tract infection | 4 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Macrocrystalline formulation with food is preferred. |
| Lower urinary tract infection | 2 mg/kg | PO | Every 6 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Macrocrystalline formulation with food is preferred. |
| Lower urinary tract infection | 4 mg/kg | PO | Every 6–8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Lower urinary tract infection | 5 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Recurrent urinary infection prevention | 3–4 mg/kg | PO | Every 24 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Only after an active infection has been treated and underlying causes investigated; give after evening urination before bed. |
| Lower urinary tract infection | 4.4 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lower urinary tract infection | 4 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Macrocrystalline formulation with food is preferred. |
| Lower urinary tract infection | 2 mg/kg | PO | Every 6 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Macrocrystalline formulation with food is preferred. |
| Lower urinary tract infection | 4 mg/kg | PO | Every 6–8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Lower urinary tract infection | 5 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Recurrent urinary infection prevention | 3–4 mg/kg | PO | Every 24 h | Do not use in: Azotemia, Pregnancy, Neonatal animals; Only after an active infection has been treated and underlying causes investigated; give after evening urination before bed. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Lower urinary tract infection | 2 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Lower urinary tract infection | 2.5–4.5 mg/kg | PO | Every 8 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
| Lower urinary tract infection | 10 mg/kg | PO | Every 24 h | Do not use in: Azotemia, Pregnancy, Neonatal animals |
Indications
- Treatment of bacterial cystitis caused by nitrofurantoin-susceptible organisms in dogs.
- Treatment of selected lower urinary tract infections caused by susceptible multidrug-resistant bacteria, including some Escherichia coli, staphylococcal or enterococcal isolates.
- Extra-label treatment of selected susceptible lower urinary infections in other veterinary species, with a smaller clinical evidence base.
Contraindications
- Azotemia
- Pregnancy, particularly near term, and neonatal patients
- Not appropriate for pyelonephritis, prostatitis, systemic infection, Proteus or Pseudomonas infection.
Interactions
- Urinary alkalinizers can reduce activity.
Adverse effects
- Nausea, vomiting, diarrhea, urine discoloration and peripheral neuropathy.
Toxicity
Neuropathy is more likely with renal impairment or prolonged exposure. Monitor renal, hepatic and neurologic effects after major exposure; no specific antidote is established. Renal impairment increases accumulation and neuropathy risk.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Nitrofurantoin macrocrystalline capsule 25 mg | Capsule | 25 mg / capsule | PO |
| Nitrofurantoin macrocrystalline capsule 50 mg | Capsule | 50 mg / capsule | PO |
| Nitrofurantoin macrocrystalline capsule 100 mg | Capsule | 100 mg / capsule | PO |
| Nitrofurantoin 50 mg | Tablet | 50 mg / tablet | PO |
| Nitrofurantoin 100 mg | Tablet | 100 mg / tablet | PO |
| Nitrofurantoin oral suspension 5 mg/mL | Oral Liquid | 5 mg / mL | PO |
Monitoring and Administration
Use urine culture and clinical response to assess treatment. Macrocrystalline capsules with food may cause less gastrointestinal irritation; increasing dose does not overcome saturable urinary secretion.
Rare drug-induced hepatopathy has been reported; check liver enzymes if adverse signs occur. Suppressive nightly therapy will not treat an existing active UTI.
Do not freeze oral nitrofurantoin suspension; avoid contact with unsuitable metals.