Dosing and uses of Macrobid, Macrodantin (nitrofurantoin)
Adult dosage forms and strengths
capsule, macrocrystals
- 25mg
- 50mg
- 100mg
capsule, monohydrate/macrocystals
- 100 mg
oral suspension
- 25mg/5mL
Urinary Tract Infection
Susceptible strains of Escherichia coli, Enterobacter spp, Klebsiella spp, Staphylococcus aureus, and S saprophyticus
Macrocrystals (Macrodantin, Furadantin, and equivalents): 50-100 mg PO q6hr for 7 days or for 3 days after obtaining sterile urine
Monohydrate/macrocrystals (Macrobid and equivalents): 100 mg PO q12hr for 7 days or for 3 days after obtaining sterile urine
Long-term prophylaxis/suppression: 50-100 mg macrocrystals PO HS for up to 12 months
Dosing Considerations
Avoid for long-term UTI suppression; possible pulmonary toxicity; safer alternatives are available
Not drug of choice in elderly because of unfavorable side-effect profile
Loses effectiveness in patients with CrCl <60 mL/min due to inadequate urine concentration (Beers criteria)
Monitor renal function; renally excreted; decreased renal function more likely in elderly
Monitor liver function and possible pulmonary reactions
Take with food or milk
Dual release macrocrystals indicated only for patients >12 years for acute UTIs (cystitis) caused by E coli or S saprophyticus
Pediatric dosage forms and strengths
capsule, macrocrystals
- 25mg
- 50mg
- 100mg
capsule, monohydrate/macrocrystals
- 100 mg
oral suspension
- 25mg/5mL
Urinary Tract Infection
>1 month
- 5-7 mg/kg/day PO divided q6hr for 7 days
- UTI prophylaxis: 1-2 mg/kg PO qHS or 2 divided doses
>12 years
- Macrocrystals (Macrodantin, Furadantin, and equivalents): 50-100 mg PO q6hr for 7 days or for 3 days after obtaining sterile urine
- Monohydrate/macrocrystals (Macrobid and equivalents): 100 mg PO q12hr for 7 days or for 3 days after obtaining sterile urine
- Long-term prophylaxis/suppression: 50-100 mg macrocrystals PO HS for up to 12 months
Dosing Considerations
Avoid for long-term UTI suppression; possible pulmonary toxicity; safer alternatives are available
Loses effectiveness in patients with CrCl <60 mL/min due to inadequate urine concentration (Beers criteria)
Monitor renal function; renally excreted; decreased renal function more likely in elderly
Monitor liver function
Take with food or milk
Dual release macrocrystals indicated only for patients >12 years for acute UTIs (cystitis) caused by E coli or S saprophyticus
Macrobid, Macrodantin (nitrofurantoin) adverse (side) effects
Frequency not defined
Anorexia
Arthralgia
Chest pains
Chills
Cough
Clostridium difficile colitis
Cyanosis secondary to methemoglobinemia
Diarrhea
Dizziness
Drowsiness
Dyspnea
Exfoliative dermatitis
Fatigue
Fever
Flatulence
Headache
Hemolytic anemia
Hepatitis
Increased LFTs
Itching
Nausea
Numbness
Paresthesia
Rash
Sore throat
Stomach upset
Vomiting
Weakness
Urine discoloration
Vasculitis
Warnings
Contraindications
Renal failure (anuria, oliguria, or CrCl <60 mL/min)
Pregnancy at term (38-42 weeks of gestation)
History of hepatic dysfunction/cholestatic jaundice with nitrofurantoin
Neonates (<28 days)
Hypersensitivity
Cautions
Caution in patients with G6PD deficiency (may increase risk for hemolytic anemia)
Avoid long-term use in the elderly (may increase risk for pulmonary toxicity)
Renal impairment
Discontinue if paresthesia or hemolysis develop
Risk of occasional hepatotoxicity and pulmonary toxicity
Protect from light
Peripheral neuropathy may occur; risk may increase in patients diagnosed with anemia, diabetes, vitamin B deficiency, or electrolyte imbalance (use caution)
Acute/chronic pulmonary reactions (eg., cough, interstitial pneumonitis or fibrosis) reported
Bacterial superinfections may occur with prolonged treatment
Pregnancy and lactation
Pregnancy category: B; contraindicated at term
Crosses placenta, but not well distributed
Lactation: Enters breast milk; discontinue drug or do not nurse
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Macrobid, Macrodantin (nitrofurantoin)
Mechanism of action
Inactivates or alters bacterial ribosomal proteins and other macromolecules that may interfere with metabolism and cell-wall synthesis
Absorption
Well absorbed; macrocrystalline form absorbed more slowly due to slower dissolution (causes less GI distress)
Bioavailability: Increased with food
Distribution
Crosses placenta, but not well distributed
Protein bound: Approximately 60-90%
Vd: 0.8 L/kg
Metabolism
Reduced by bacterial flavoproteins to reactive intermediates
Body tissues (except plasma) metabolize 60% of drug to inactive metabolites
Elimination
Half-life: 20-60 min; prolonged with renal impairment
Excretion: Urine (40%); feces (small amounts)
