Dosage guidance:
Dosage form information: Nitrofurantoin is available in the United States as a combination product (nitrofurantoin monohydrate and nitrofurantoin macrocrystals [Macrobid]), which is typically dosed twice daily for the treatment of acute infections, and a preparation that consists solely of nitrofurantoin macrocrystals (oral suspension, Macrodantin), which is typically dosed 4 times daily for the treatment of acute infections. Regardless of the formulation used, advise patients to administer with food to improve absorption.
Asymptomatic bacteriuria (≥105 CFU per mL) in pregnancy:
Note: Although contraindicated by the manufacturer in pregnant patients at term (38 to 42 weeks' gestation), during labor and delivery, or when the onset of labor is imminent due to the possibility of hemolytic anemia in the newborn, the American College of Obstetricians and Gynecologists does not restrict use of nitrofurantoin during the third trimester. Based on available safety data, nitrofurantoin may also be used as an alternative therapy during the first trimester (Ref).
Nitrofurantoin monohydrate/macrocrystals (Macrobid): Oral: 100 mg twice daily for 5 to 7 days (Ref).
Cystitis, acute uncomplicated or acute simple cystitis (infection limited to the bladder without signs/symptoms of upper tract, prostate, or systemic infection), treatment:
Note: Consider use of a different empiric agent in patients with suspected pyelonephritis, patients who have received nitrofurantoin in the last 3 months, or patients who have had a urine isolate with documented resistance to nitrofurantoin in the last 3 months (Ref).
Nitrofurantoin monohydrate/macrocrystals (Macrobid): Oral: 100 mg twice daily; treat females for 5 days and males for 7 days (Ref).
Nitrofurantoin macrocrystals (oral suspension, Macrodantin): Oral: 50 to 100 mg every 6 hours; treat females for 5 days and males for 7 days (Ref). Note: The recommended duration of therapy with this formulation is based on the recommendation for the nitrofurantoin monohydrate/macrocrystal formulation as well as expert opinion.
Cystitis, prophylaxis for recurrent infection:
Note: May be considered in nonpregnant women with bothersome, frequently recurrent cystitis despite nonantimicrobial preventive measures. The optimal duration has not been established; duration ranges from 3 to 12 months, with periodic reassessment (Ref). Prolonged use (>6 months) of nitrofurantoin has been associated with diffuse interstitial pneumonitis and/or pulmonary fibrosis, chronic hepatitis, and the development of neuropathy (Ref).
Continuous prophylaxis:
Nitrofurantoin monohydrate/macrocrystals (Macrobid) (off-label use): Oral: 100 mg once daily at bedtime (Ref).
Nitrofurantoin macrocrystals (oral suspension, Macrodantin): Oral: 50 to 100 mg once daily at bedtime.
Postcoital prophylaxis (females with cystitis temporally related to sexual intercourse):
Nitrofurantoin monohydrate/macrocrystals (Macrobid) (off-label use): Oral: 100 mg as a single dose taken within 2 hours of sexual intercourse (Ref).
Nitrofurantoin macrocrystals (oral suspension, Macrodantin): Oral: 50 to 100 mg as a single dose taken within 2 hours of sexual intercourse (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason A Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Altered kidney function:
CrCl ≥60 mL/minute: No dosage adjustment necessary.
CrCl 30 to <60 mL/minute: Although contraindicated in the manufacturer's labeling, limited data suggest nitrofurantoin is safe and effective for short-term treatment of uncomplicated acute cystitis in patients with an eGFR or CrCl 30 to 60 mL/minute (Ref). One retrospective cohort study reported increased risk of pulmonary adverse events in patients with eGFR <50 mL/minute (Ref).
CrCl <30 mL/minute: Avoid use (Ref).
Hemodialysis, intermittent (thrice weekly): Avoid use (Ref).
Peritoneal dialysis: Avoid use (Ref).
CRRT: Avoid use (Ref).
PIRRT (eg, sustained low-efficiency diafiltration): Avoid use (Ref).
There are no dosage adjustments provided in the manufacturer's labeling. Contraindicated in patients with a previous history of cholestatic jaundice or hepatic dysfunction associated with nitrofurantoin.
Cystitis, prophylaxis for recurrent infection: Avoid for long-term suppression; alternative agents preferred (Ref).
Cystitis, acute uncomplicated or acute simple cystitis, treatment: Refer to adult dosing.
(For additional information see "Nitrofurantoin: Pediatric drug information")
Dosage guidance:
Dosage form information: Oral suspension products are available in 2 concentrations (25 mg/5 mL [5 mg/mL] and 50 mg/5 mL [10 mg/mL]); verify product selection and avoid confusion between the different concentrations; dose should be clearly presented as "mg" instead of "mL."
Urinary tract infection (UTI), treatment: Note: Reserve for cystitis; should not be used for pyelonephritis or to treat febrile infants with UTI because renal and serum concentrations may not be adequate (Ref).
Furadantin, Macrodantin:
Weight-directed dosing: Infants, Children, and Adolescents: Oral: 5 to 7 mg/kg/day divided every 6 hours for 7 days; maximum dose: 100 mg/dose.
Fixed dosing: Infants, Children, and Adolescents: Furadantin oral suspension:
≤4 kg: Oral: 5 mg every 6 hours.
>4 to 5 kg: Oral: 7 mg every 6 hours.
>5 to 7 kg: Oral: 9 mg every 6 hours.
>7 to 10 kg: Oral: 12.5 mg every 6 hours.
>10 to 14 kg: Oral: 17.5 mg every 6 hours.
>14 to 20 kg: Oral: 25 mg every 6 hours.
>20 to 25 kg: Oral: 35 mg every 6 hours.
>25 to 30 kg: Oral: 42.5 mg every 6 hours.
>30 to 40 kg: Oral: 50 mg every 6 hours.
≥40 kg: Oral: 50 to 100 mg every 6 hours.
Macrobid (macrocrystal/monohydrate): Adolescents: Oral: 100 mg every 12 hours for 7 days.
Urinary tract infection, prophylaxis: Furadantin, Macrodantin: Infants, Children, and Adolescents: Oral: 1 to 2 mg/kg/day in a single dose (at bedtime) or divided twice daily; maximum daily dose: 100 mg/day. Note: In infants and children <24 months, prophylaxis should only be considered for those with grade III or V reflux or with recurrent febrile UTI; data supporting the routine use of continuous antimicrobial prophylaxis are limited (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Altered kidney function: Infants, Children, and Adolescents:
CrCl ≥60 mL/minute: There are no dosage adjustments provided in the manufacturer's labeling; based on experience in adults, no dosage adjustment necessary (Ref).
CrCl 30 to <60 mL/minute: Use is contraindicated per the manufacturer's labeling. In adults, limited data suggest nitrofurantoin is safe and effective for short-term treatment of uncomplicated acute cystitis in patients with an eGFR or CrCl 30 to 60 mL/minute (Ref). One retrospective cohort study reported increased risk of pulmonary adverse events in adult females with eGFR <50 mL/minute (Ref).
CrCl <30 mL/minute: Use is contraindicated (manufacturer's labeling).
Hemodialysis, intermittent (thrice weekly): Based on adult information, avoid use (likely to be ineffective) (Ref).
Peritoneal dialysis: Based on adult information, avoid use (likely to be ineffective) (Ref).
Infants, Children, and Adolescents: There are no dosage adjustments provided in manufacturer's labeling. Contraindicated in patients with a previous history of cholestatic jaundice or hepatic dysfunction associated with nitrofurantoin.
Clostridioides difficile infection has occurred with nitrofurantoin, including Clostridioides difficile associated diarrhea and Clostridioides difficile colitis (Ref).
Onset: Varied; may start on the first day of antibiotic therapy or up to 3 months postantibiotic (Ref).
Risk factors:
• Antibiotic exposure (highest risk factor) (Ref)
• Type of antibiotic (Ref)
• Long durations in a hospitalization or other health care setting (recent or current) (Ref)
• Older adults (Ref)
• Immunocompromised conditions (Ref)
• A serious underlying condition (Ref)
• GI surgery/manipulation (Ref)
• Antiulcer medications (eg, proton pump inhibitors, H2 blockers) (Ref)
• Chemotherapy (Ref)
A wide range of drug-induced liver injury (DILI) has been reported with nitrofurantoin, including acute hepatitis, granulomatous reaction, cholestatic jaundice, autoimmune hepatitis, and chronic active hepatitis that may lead to hepatic cirrhosis or death (Ref). Acute liver injury usually presents with a hepatocellular pattern with or without jaundice and is commonly associated with fever and skin rash and typically resolves with discontinuation. Chronic liver injury usually presents with autoimmune features and is associated with fatigue, weakness, dark urine, and jaundice (Ref).
Mechanism: Not clearly established; oxidative-free radicals may damage hepatocytes. An autoimmune mechanism may also contribute (Ref).
Onset: Varied; acute liver injury may vary in onset from 1 to 6 weeks of use and chronic liver injury may vary in onset from months (typically >6 months) to years of use (Ref).
Risk factors:
• Older patients (Ref)
• Females (Ref)
• Prolonged use (>6 months) (Ref)
Peripheral neuropathy may occur with nitrofurantoin and typically presents as sensorimotor polyneuropathy (Ref).
Mechanism: Non–dose-related; idiosyncratic (Ref).
Risk factors:
• Older patients
• Anemia
• Debilitating disease
• Diabetes
• Electrolyte imbalance
• Kidney impairment (CrCl <60 mL/minute)
• Vitamin B deficiency
Pulmonary toxicity may occur with nitrofurantoin and ranges from acute pulmonary reaction, subacute pulmonary reaction, and/or chronic pulmonary reaction (Ref).
Mechanism: Acute reactions: Non–dose-related; immunologic (Ref). Chronic reactions: Unknown. May be T-cell mediated (non–dose-related) or direct toxicity (dose-related) (Ref).
Onset: Varied; acute reactions can vary in onset from days to weeks while chronic reactions often occurs after months to years of use (Ref).
Risk factors:
• Older patients (Ref)
• Females (Ref)
• Prolonged use (>6 months) (for chronic pulmonary reactions) (Ref)
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
1% to 10%:
Endocrine & metabolic: Increased serum phosphate (1% to 5%)
Gastrointestinal: Flatulence (2%), nausea (8%)
Hematologic & oncologic: Decreased hemoglobin (1% to 5%), eosinophilia (1% to 5%)
Hepatic: Increased serum alanine aminotransferase (1% to 5%), increased serum aspartate aminotransferase (1% to 5%)
Nervous system: Headache (6%)
<1%:
Dermatologic: Alopecia, pruritus, urticaria
Gastrointestinal: Abdominal pain, constipation, diarrhea, dyspepsia, vomiting
Nervous system: Chills, dizziness, drowsiness, malaise
Ophthalmic: Amblyopia
Respiratory: Acute pulmonary reaction (including cough, dyspnea, dyspnea on exertion, pleural effusion, pleuritic chest pain, pulmonary infiltrates)
Miscellaneous: Fever
Frequency not defined: Respiratory: Chronic pulmonary reaction (including diffuse interstitial pneumonitis, pulmonary fibrosis), subacute pulmonary reaction
Postmarketing:
Cardiovascular: Bundle branch block (Dibagh Gandorta 2017), ECG changes, nonspecific T wave on ECG, vasculitis
Dermatologic: Eczematous rash, erythema multiforme, exfoliative dermatitis, maculopapular rash, Stevens-Johnson syndrome (Davis 2018)
Gastrointestinal: Anorexia, Clostridioides difficile associated diarrhea (Hirschhorn 1994), Clostridioides difficile colitis, pancreatitis (Mouallen 2003), sialadenitis
Hematologic & oncologic: Agranulocytosis (Roberts 2005), aplastic anemia, glucose-6-phosphate dehydrogenase deficiency anemia, granulocytopenia, hemolytic anemia, leukopenia, megaloblastic anemia, methemoglobinemia, thrombocytopenia (Dibagh Gandorta 2017)
Hepatic: Autoimmune hepatitis (Sakaan 2014), cholestatic jaundice (Sakaan 2014), chronic active hepatitis (Sakaan 2014), hepatic cirrhosis (Sakaan 2014), hepatic necrosis (Sakaan 2014), hepatitis (acute) (Sakaan 2014)
Hypersensitivity: Anaphylaxis, angioedema
Nervous system: Asthenia, bulging fontanel (infants), confusion, depression, idiopathic intracranial hypertension, peripheral neuropathy (Tan 2012), psychotic reaction, vertigo
Neuromuscular & skeletal: Arthralgia, lupus-like syndrome, myalgia
Ophthalmic: Nystagmus disorder, optic neuritis
Respiratory: Cyanosis
Anuria, oliguria, or significant impairment of renal function (creatinine clearance [CrCl] <60 mL/minute or clinically significant elevated serum creatinine); previous history of cholestatic jaundice or hepatic dysfunction associated with prior nitrofurantoin use; hypersensitivity to drug or any component of the formulation.
Note: The manufacturer's contraindication in patients with CrCl <60 mL/minute has been challenged in the literature; limited data suggest that an alternative creatinine clearance threshold may be considered (Oplinger 2013).
Because of the possibility of hemolytic anemia caused by immature erythrocyte enzyme systems (glutathione instability), the drug is contraindicated in pregnant patients at term (38 to 42 weeks gestation), during labor and delivery, or when the onset of labor is imminent; also contraindicated in neonates younger than 1 month of age.
Concerns related to adverse effects:
• Superinfection: Prolonged use may result in fungal or bacterial superinfection.
Disease-related concerns:
• Hemolytic anemia: Use caution in patients with G6PD deficiency; may be at increased risk for hemolytic anemia. Discontinue therapy if occurs.
• Hepatic impairment: Use is contraindicated in patients with a history of nitrofurantoin associated cholestatic jaundice or hepatic dysfunction.
• Renal impairment: Urinary nitrofurantoin concentrations are variable in patients with impaired renal function. Use with caution. The manufacturer contraindicates use in CrCl <60 mL/minute; however, limited data suggest nitrofurantoin is safe and effective for short-term treatment of uncomplicated urinary tract infection (UTI) in patients with CrCl 30 to 60 mL/minute (Cuhna 2017; Oplinger 2013; Santos 2016; Singh 2015).
Special populations:
• Older adult: Avoid long-term use in older adult patients.
• Pediatric: Use is contraindicated in children <1 month of age (at increased risk for hemolytic anemia).
Other warnings/precautions:
• Appropriate use: Pyelonephritis: Not indicated for the treatment of pyelonephritis or perinephric abscesses.
Nitrofurantoin should not be used to treat UTIs in febrile infants and young children; nitrofurantoin concentrates in the urine and does not reach therapeutic serum and possibly parenchymal concentrations making it ineffective to treat pyelonephritis or urosepsis (AAP 2011).
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, Oral:
Macrobid: 100 mg [contains fd&c blue #1 (brilliant blue), fd&c red #40 (allura red ac dye), quinoline yellow (d&c yellow #10)]
Macrodantin: 25 mg
Macrodantin: 50 mg, 100 mg [contains fd&c yellow #6 (sunset yellow), quinoline yellow (d&c yellow #10)]
Generic: 25 mg, 50 mg, 100 mg
Suspension, Oral:
Generic: 25 mg/5 mL (230 mL, 240 mL); 50 mg/5 mL (60 mL)
Yes
Capsules (Macrobid Oral)
100 mg (per each): $7.14
Capsules (Macrodantin Oral)
25 mg (per each): $14.06
50 mg (per each): $3.15
100 mg (per each): $6.62
Capsules (Nitrofurantoin Macrocrystal Oral)
25 mg (per each): $7.03 - $12.64
50 mg (per each): $2.13 - $2.43
100 mg (per each): $3.38 - $3.53
Capsules (Nitrofurantoin Monohyd Macro Oral)
100 mg (per each): $2.77 - $6.78
Suspension (Nitrofurantoin Oral)
25 mg/5 mL (per mL): $3.18 - $14.61
50 mg/5 mL (per mL): $56.00
Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Capsule, Oral:
Macrobid: 100 mg [DSC] [contains corn starch, edetate (edta) calcium disodium, fd&c blue #1 (brilliant blue), fd&c red #40 (allura red ac dye), quinoline yellow (d&c yellow #10)]
Generic: 50 mg, 100 mg
Tablet, Oral:
Generic: 50 mg, 100 mg
Oral: Administer with meals to improve absorption and decrease adverse effects; suspension may be mixed with water, milk, or fruit juice. Shake suspension well before use. The monohydrate/macrocrystals capsules (twice-daily formulation [Macrobid]) should not be opened; the macrocrystals capsules (4-times-daily formulation [Macrodantin]) may be opened and the contents mixed with food or juice for immediate use (data on file from manufacturer).
Oral: Administer with food to improve absorption and decrease adverse effects. Shake suspension well before use and administer using an oral dosing syringe. The monohydrate/macrocrystals capsules (twice-daily formulation [eg, Macrobid]) should not be opened; the macrocrystals capsules (4-times-daily formulation [eg, Macrodantin]) may be opened and the contents mixed with food or juice for immediate use (data on file from manufacturer).
Cystitis, acute uncomplicated, treatment:
Nitrofurantoin monohydrate/macrocrystals (Macrobid): Treatment of acute uncomplicated cystitis caused by susceptible strains of Escherichia coli or Staphylococcus saprophyticus in patients ≥12 years of age.
Nitrofurantoin macrocrystals (oral suspension, Macrodantin): Treatment of acute uncomplicated cystitis when caused by susceptible strains of E. coli, enterococci, Staphylococcus aureus, and certain susceptible strains of Klebsiella and Enterobacter species.
Limitations of use: Not indicated for treatment of pyelonephritis or perinephric abscess.
Cystitis, prophylaxis for recurrent infection: Nitrofurantoin macrocrystals (oral suspension, Macrodantin): Chronic suppression of recurrent urinary tract infection.
Macrobid may be confused with microK, Nitro-Bid.
Nitrofurantoin may be confused with Neurontin, nitroglycerin.
Beers Criteria: Nitrofurantoin is identified in the Beers Criteria as a potentially inappropriate medication to be avoided in patients 65 years and older (independent of diagnosis or condition) due to its potential for pulmonary toxicity, hepatotoxicity and peripheral neuropathy, particularly when given long-term; safer alternatives exist. Avoid use in patients with a CrCl less than 30 mL/minute or for long-term suppressive therapy (Beers Criteria [AGS 2023]).
KIDs List: Nitrofurantoin, when used in neonates, is identified on the Key Potentially Inappropriate Drugs in Pediatrics (KIDs) list; use should be avoided due to risk of hemolytic anemia (weak recommendation; very low quality of evidence) (PPA [Meyers 2020]).
None known.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.
Bacillus clausii: Antibiotics may diminish the therapeutic effect of Bacillus clausii. Management: Bacillus clausii should be taken in between antibiotic doses during concomitant therapy. Risk D: Consider therapy modification
BCG (Intravesical): Antibiotics may diminish the therapeutic effect of BCG (Intravesical). Risk X: Avoid combination
BCG Vaccine (Immunization): Antibiotics may diminish the therapeutic effect of BCG Vaccine (Immunization). Risk C: Monitor therapy
Cholera Vaccine: Antibiotics may diminish the therapeutic effect of Cholera Vaccine. Management: Avoid cholera vaccine in patients receiving systemic antibiotics, and within 14 days following the use of oral or parenteral antibiotics. Risk X: Avoid combination
Dapsone (Topical): May enhance the adverse/toxic effect of Methemoglobinemia Associated Agents. Risk C: Monitor therapy
Fecal Microbiota (Live) (Oral): May diminish the therapeutic effect of Antibiotics. Risk X: Avoid combination
Fecal Microbiota (Live) (Rectal): Antibiotics may diminish the therapeutic effect of Fecal Microbiota (Live) (Rectal). Risk X: Avoid combination
Immune Checkpoint Inhibitors (Anti-PD-1, -PD-L1, and -CTLA4 Therapies): Antibiotics may diminish the therapeutic effect of Immune Checkpoint Inhibitors (Anti-PD-1, -PD-L1, and -CTLA4 Therapies). Risk C: Monitor therapy
Lactobacillus and Estriol: Antibiotics may diminish the therapeutic effect of Lactobacillus and Estriol. Risk C: Monitor therapy
Local Anesthetics: Methemoglobinemia Associated Agents may enhance the adverse/toxic effect of Local Anesthetics. Specifically, the risk for methemoglobinemia may be increased. Risk C: Monitor therapy
Magnesium Trisilicate: May decrease the absorption of Nitrofurantoin. Risk X: Avoid combination
Nitric Oxide: May enhance the adverse/toxic effect of Methemoglobinemia Associated Agents. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Risk C: Monitor therapy
Norfloxacin: Nitrofurantoin may diminish the therapeutic effect of Norfloxacin. Risk X: Avoid combination
Prilocaine: Methemoglobinemia Associated Agents may enhance the adverse/toxic effect of Prilocaine. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Management: Monitor patients for signs of methemoglobinemia (e.g., hypoxia, cyanosis) when prilocaine is used in combination with other agents associated with development of methemoglobinemia. Avoid lidocaine/prilocaine in infants receiving such agents. Risk C: Monitor therapy
Probenecid: May diminish the therapeutic effect of Nitrofurantoin. Probenecid may increase the serum concentration of Nitrofurantoin. Risk C: Monitor therapy
Sodium Nitrite: Methemoglobinemia Associated Agents may enhance the adverse/toxic effect of Sodium Nitrite. Combinations of these agents may increase the likelihood of significant methemoglobinemia. Risk C: Monitor therapy
Sodium Picosulfate: Antibiotics may diminish the therapeutic effect of Sodium Picosulfate. Management: Consider using an alternative product for bowel cleansing prior to a colonoscopy in patients who have recently used or are concurrently using an antibiotic. Risk D: Consider therapy modification
Typhoid Vaccine: Antibiotics may diminish the therapeutic effect of Typhoid Vaccine. Only the live attenuated Ty21a strain is affected. Management: Avoid use of live attenuated typhoid vaccine (Ty21a) in patients being treated with systemic antibacterial agents. Postpone vaccination until 3 days after cessation of antibiotics and avoid starting antibiotics within 3 days of last vaccine dose. Risk D: Consider therapy modification
Nitrofurantoin serum concentrations may be increased if taken with food. Management: Administer with meals.
Nitrofurantoin in doses >10 mg/kg/day may cause spermatogenic arrest and decrease sperm count. This was observed in some patients treated for 2 weeks; sperm counts returned to normal between 13 and 32 weeks after therapy was discontinued. Consider avoiding use in patients planning to father a child (Drobnis 2017).
Nitrofurantoin crosses the placenta (Perry 1967).
Current studies evaluating maternal use of nitrofurantoin during pregnancy and the development of congenital anomalies have had mixed results (ACOG 2023; Crider 2009; Goldberg 2013; Goldberg 2015; Muanda 2017; Nordeng 2013). An increased risk of neonatal jaundice was observed following maternal nitrofurantoin use during the last 30 days of pregnancy (Nordeng 2013).
Due to pregnancy-induced physiologic changes, some pharmacokinetic properties of nitrofurantoin may be altered. Based on a study of 30 women administered nitrofurantoin prior to abortion, maternal serum concentrations of nitrofurantoin may be decreased and urine concentrations may be increased during pregnancy (Philipson 1979).
Urinary tract infections are associated with adverse pregnancy outcomes including preterm birth and delivery of low-birth-weight infants. Treatment with a targeted antibiotic is recommended when asymptomatic bacteriuria or acute cystitis are diagnosed. According to the manufacturer, nitrofurantoin is contraindicated in pregnant patients at term (38 to 42 weeks' gestation), during labor and delivery, or when the onset of labor is imminent due to the possibility of hemolytic anemia in the newborn. However, nitrofurantoin may be used for the treatment of asymptomatic bacteriuria and acute cystitis in pregnant patients when appropriate. Nitrofurantoin may be used in the first trimester when alternative antibiotics cannot be used and may be considered as a first-line antibiotic in the second and third trimesters. Avoid use in pregnant patients with G6PD deficiency (ACOG 2023).
Nitrofurantoin is present in breast milk.
Multiple studies have evaluated nitrofurantoin in breast milk (Gerk 2001; Hosbach 1967; Pons 1990; Varsano 1973).
Data are available from 9 lactating patients following use of nitrofurantoin 100 mg every 6 hours for 4 doses on day 1 with an additional dose the morning of day 2. Breast milk and maternal serum were sampled 2 hours after the fifth dose. Following a fifth dose of 100 mg in 5 patients, trace amounts of nitrofurantoin were detectable in the breast milk of only 1 patient; maternal serum concentrations ranged from trace amounts to 0.6 mcg/mL. Four patients were administered nitrofurantoin 200 mg as the fifth dose. Maternal serum concentrations of nitrofurantoin ranged from 0.2 to 1.6 mcg/mL. Breast milk concentrations ranged from 0 to 0.5 mcg/mL. The postpartum age of the lactating patients was not noted (Varsano 1973).
Breast milk was sampled from 6 patients between postpartum days 3 and 6 following administration of nitrofurantoin 50 mg (n = 3) or 100 mg (n = 3) three times daily for 4 doses. Breast milk was sampled prior to and 3 and 6 hours after the dose. Three hours after the 50 mg dose, nitrofurantoin concentrations in breast milk ranged from 0.2 to 0.7 mcg/mL. Breast milk concentrations of nitrofurantoin were 0.62 to 2.22 mcg/mL 3 hours following the 100 mg dose. Nitrofurantoin was not detectable in samples obtained prior to the fourth dose (Pons 1990).
Nitrofurantoin concentrations in breast milk were evaluated in 4 lactating patients between 8 and 26 weeks postpartum. Breast milk and serum were sampled at intervals over 12 hours following a single dose of nitrofurantoin 100 mg. Peak breast milk concentrations occurred between 4 and 6 hours after the dose. The maximum concentrations of nitrofurantoin in breast milk ranged from 2.13 to 3.32 mcg/mL (mean 2.71 mcg/mL). Authors of the study used the mean milk concentration for the 12-hour dosing interval (1.3 mcg/mL) to calculate the estimated dose of nitrofurantoin received by a breastfeeding infant to be 0.2 mg/kg/day (relative infant dose [RID] 6%, based on weight adjusted maternal dose and a 60 kg mother) (Gerk 2001). In general, breastfeeding is considered acceptable when the RID is <10% (Anderson 2016; Ito 2000).
A prospective cohort study evaluated the outcomes of breastfed infants whose mothers were taking various medications. Among 6 mother-infant pairs with reported nitrofurantoin exposure (dose, duration, relationship to breastfeeding not provided), diarrhea was reported in 2 infants and decreased milk volume was reported by 1 mother (Ito 1993). In general, antibiotics that are present in breast milk may cause non–dose-related modification of bowel flora. Monitor infants for GI disturbances (WHO 2002).
The therapeutic use of nitrofurantoin is contraindicated in neonates (<1 month of age) due to the possibility of hemolytic anemia caused by immature erythrocyte enzyme systems. Theoretically, this risk is also present in breastfeeding neonates exposed to nitrofurantoin via breast milk (Zao 2014). When breastfeeding infants <1 month of age, the manufacturer recommends a decision be made whether to discontinue breastfeeding or to discontinue the drug, considering the importance of treatment to the mother. In addition, the World Health Organization states that nitrofurantoin is compatible with breastfeeding for healthy full-term infants with monitoring for adverse reactions (eg, jaundice, hemolysis). However, patients taking nitrofurantoin should avoid breastfeeding premature neonates or neonates <1 month of age (WHO 2002).
Avoidance of breastfeeding should also be considered in infants of any age where absolute or relative G6PD deficiency may be present (eg, Eastern Mediterranean, African, and Southeast Asian populations) due to the risk of hemolytic anemia (WHO 2002; Zao 2014).
Take with meals to improve absorption and decrease adverse effects.
Signs or symptoms of pulmonary reaction (eg, malaise, dyspnea, cough, fever, radiologic evidence of diffuse interstitial pneumonitis or fibrosis); signs of numbness or tingling of the extremities; CBC, periodic LFTs, periodic renal function tests with long-term use.
Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates that inactivate or alter bacterial ribosomal proteins leading to inhibition of protein synthesis, aerobic energy metabolism, DNA, RNA, and cell wall synthesis. Nitrofurantoin is bactericidal in urine at therapeutic doses. The broad-based nature of this mode of action may explain the lack of acquired bacterial resistance to nitrofurantoin, as the necessary multiple and simultaneous mutations of the target macromolecules would likely be lethal to the bacteria.
Absorption: Well absorbed; macrocrystalline form absorbed more slowly due to slower dissolution (causes less GI distress)
Distribution: Vd: 0.8 L/kg
Protein binding: 60% to 90%
Metabolism: Body tissues (except plasma) metabolize 60% of drug to inactive metabolites
Bioavailability: Increased with food by ~40%
Half-life elimination: 20 to 60 minutes; prolonged with renal impairment
Excretion:
Suspension: Urine (~40%) and feces (small amounts) as metabolites and unchanged drug
Macrocrystals: Urine (20% to 25% as unchanged drug)
Altered kidney function: Nitrofurantoin accumulates in serum.
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