Nitrofurantoin
Synthetic nitrofuran antibacterial
Also known as: Macrodantin · Macrobid · Furadantin · furadoninum · nitrofurantoinum · Nitrofurantoine
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prevention of re-infections with gram-negative organisms | 4 mg/kg | PO | q24h | Long-term | 🌎 NA |
| Recurrent UTI (Conventional dose) | 4 mg/kg | PO | q8h | — | 🌎 NA |
| Recurrent UTI (Prophylactic dose) | 3-4 mg/kg | PO | q24h | — | 🌎 NA |
| Susceptible bacterial urinary tract infections | 4 mg/kg | PO | q6-8h | — | 🌎 NA |
| Susceptible bacterial urinary tract infections | 5 mg/kg | PO | q8h | — | 🌎 NA |
| Susceptible bacterial urinary tract infections | 4.4 mg/kg | PO | q8h | — | 🌎 NA |
| Urinary tract infections (lower UTI only) | 4.4-5 mg/kg | PO | q8h | As directed by culture and sensitivity | 🌍 EU |
- Prevention of re-infections with gram-negative organisms: 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 (Prophylactic dose): Should be given at night after micturition and immediately before bedtime.
- Susceptible bacterial urinary tract infections: Listed as three times daily.
- Urinary tract infections (lower UTI only): For urinary tract infections only. Not for pyelonephritis.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible bacterial urinary tract infections | 5 mg/kg | PO | q8h | — | 🌎 NA |
| Recurrent UTI (Conventional dose) | 4 mg/kg | PO | q8h | — | 🌎 NA |
| Recurrent UTI (Prophylactic dose) | 3-4 mg/kg | PO | q24h | — | 🌎 NA |
| Susceptible bacterial urinary tract infections | 4 mg/kg | PO | q6-8h | — | 🌎 NA |
| Urinary tract infections (lower UTI only) | 4.4-5 mg/kg | PO | q8h | As directed by culture and sensitivity | 🌍 EU |
- Recurrent UTI (Prophylactic dose): Should be given at night after micturition and immediately before bedtime.
- Urinary tract infections (lower UTI only): For urinary tract infections only. Not for pyelonephritis.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible urinary tract infections | 2.5-4.5 mg/kg | PO | q8h | — | 🌎 NA |
| Susceptible urinary tract infections | 10 mg/kg | PO | q24h | — | 🌎 NA |
- Susceptible urinary tract infections: Listed as three times daily.
- Susceptible urinary tract infections: Listed as daily.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Nitrofurantoin is a synthetic nitrofuran antibacterial agent primarily used as a urinary tract antiseptic.
- Site-Specific Efficacy: Because it is rapidly eliminated into the urine, it achieves high concentrations in the lower urinary tract but does not reach therapeutic concentrations in systemic circulation or tissues. Therefore, it is highly effective for lower urinary tract infections (UTIs) but is ineffective for systemic infections, pyelonephritis (kidney infections), or perinephric abscesses.
- Spectrum of Activity: It is active against many gram-negative and gram-positive organisms, including E. coli, Klebsiella, Staphylococcus, and Enterococcus. It is notably ineffective against Pseudomonas spp. and most strains of Proteus.
- Clinical Pearl: Due to increasing resistance to first-line antibiotics, nitrofurantoin is often reserved for multidrug-resistant lower UTIs, particularly those caused by resistant E. coli or Enterococcus species.
Mechanism of action
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.
Safety & warnings
Contraindications
- Renal impairment (decreased efficacy and increased risk of systemic toxicity)
- Known hypersensitivity to nitrofurantoin
- Pregnant patients at term (risk of hemolytic anemia in 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
Adverse effects
- 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)
- Prolonged bleeding times (at high doses)
Precautions
Renal Function Warning: Do not use in patients with compromised renal function. The drug relies on renal excretion to reach the site of infection (the bladder); poor kidney function means the drug won't work for the UTI and will accumulate in the blood, causing toxicity.
- Hepatotoxicity: Can cause drug-induced hepatopathy. Monitor liver enzymes if adverse effects are suspected, especially during long-term prophylactic use.
- Reproductive Warning: May cause infertility in male dogs. Use with caution in breeding animals.
- Lab Interference: May cause false-positive urine glucose results if using cupric-sulfate solutions (e.g., Clinitest). May also cause decreases in blood glucose and increases in serum creatinine, bilirubin, and ALP.
Drug interactions
Nitrofurantoin may antagonize the antimicrobial activity of fluoroquinolones; concomitant use should be avoided.
May increase the oral bioavailability and absorption of nitrofurantoin.
May inhibit the oral absorption of nitrofurantoin.
May inhibit the renal excretion of nitrofurantoin, potentially increasing systemic toxicity and reducing its effectiveness in the urinary tract.
Delays gastric emptying time and increases absorption/bioavailability of nitrofurantoin
Delays gastric emptying time and increases absorption/bioavailability of nitrofurantoin
Antagonism of antibacterial efficacy
May increase the hyperkalaemic effects of spironolactone
Significantly decreases the antibacterial activity of nitrofurantoin
Monitoring
- 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
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed from the GI tract. Presence of food enhances absorption. Macrocrystalline forms are absorbed more slowly, resulting in less GI upset and prolonged urine levels.
Distribution
Therapeutic levels in systemic circulation are not maintained due to rapid elimination. Approximately 20-60% is bound to serum proteins. Crosses the placenta; minimal quantities found in milk.
Metabolism
Some of the drug is metabolized, primarily in the liver.
Elimination
Rapidly eliminated. Approximately 40-50% is excreted into urine unchanged via both glomerular filtration and tubular secretion. Peak urine levels occur within 30 minutes of dosing.
Overdose
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.
Available products
Formulations
- Oral capsules (macrocrystals)
- Oral capsules (monohydrate/macrocrystals)
- 50 mg tablet
- 100 mg tablet
- 25 mg/5 ml oral suspension
Human-labeled
- Nitrofurantoin Macrocrystals Oral Capsules: 25 mg, 50 mg & 100 mg (Macrodantin, generic)
- Nitrofurantoin Monohydrate/Macrocrystals Oral Capsules: 100 mg (Macrobid, generic)
- Nitrofurantoin Oral Suspension: 25 mg/5 mL (5 mg/mL) (Furadantin)
- Nitrofurantoin 50 mg tablets
- Nitrofurantoin 100 mg tablets
- Nitrofurantoin 25 mg/5 ml oral suspension
Regulatory status
Banned for use in food-producing animals (Annex IV / Table 2 substance).
Human POM used under the prescribing cascade. Banned in food-producing animals.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in tight containers at room temperature and protect from light. Do not freeze the oral suspension. Nitrofurantoin will decompose if it comes into contact with metals other than aluminum or stainless steel.
Client information
Nitrofurantoin is an antibiotic specifically used to treat bladder infections. It concentrates in the urine to kill bacteria but does not work for infections in other parts of the body.
- Give with Food: Always give this medication with a meal or a treat. This significantly reduces stomach upset (vomiting) and helps the body absorb the drug better.
- Timing is Key: If your pet is on a once-daily preventative dose, give it right at bedtime, immediately after their last bathroom break for the night. This allows the medication to sit in the bladder overnight and fight bacteria.
- Watch for Side Effects: The most common side effect is vomiting. If vomiting is severe or persists, contact your veterinarian.
- Liver Warning: Rarely, this drug can affect the liver. Contact your vet immediately if you notice yellowing of the eyes or gums, severe lethargy, or loss of appetite.
- Finish the Prescription: Even if your pet seems to feel better, finish the entire course of antibiotics to prevent the infection from returning or becoming resistant.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.