• Type: Antibiotic
  • Dosage Forms: oral
  • Common Trade Names: Macrobid

Adult Dosing

Cystitis, acute uncomplicated or acute simple:[1]

  • Monohydrate/macrocrystals (Macrobid): 100mg PO q12h
  • Macrocrystals: 50-100mg PO 4 times daily for 5 days

Cystitis, recurrent, prophylaxis (continuous):[2]

  • Monohydrate/macrocrystals (Macrobid): 100mg PO daily at bedtime
  • Macrocrystals: 50-100mg PO daily at bedtime

Cystitis, postcoital prophylaxis

  • Monohydrate/macrocrystals (Macrobid): 100mg PO once within 2 hours of sexual intercourse
  • Macrocrystals: 50-100mg PO once within 2 hours of sexual intercourse

Pediatric Dosing

  • >12yo: same as adult dosing

Special Populations

  • Pregnancy Rating: B
  • Lactation Risk: Infant risk minimal
  • Renal Dosing: Contraindicated if CrCl <60
  • Hepatic dosing:


  • Allergy to class/drug
  • Neonates, pregnant women at term or when delivery imminent
  • Renal failure due to accumulation of metabolites that may cause peripheral neuropathy[3]
  • CrCL < 60, oliguria, anuria
  • Cholestatic jaundice history

Adverse Reactions


  • Hemolytic anemia can occur in patients with G6PD deficiency and in infants less than 1 month old
  • Hepatic necrosis
  • Hepatitis
  • Cholestatic jaundice syndrome
  • Erythema multiforme/SJS
  • Pancreatitis
  • Peripheral neuropathy
  • Pulmonary hypersensitivity
  • Agranulocytosis
  • Leukopenia
  • Thrombocytopenia
  • Pneumonitis
  • Pulmonary fibrosis
  • Cyanosis
  • ECG abnormality
  • C. difficle associated diarrhea
  • Optic neuritis
  • Pseudotumor cerebri
  • Psychosis
  • Vasculitis



  • Half-life: 45-60min
  • Metabolism: Hepatic
  • Excretion: Urine primarily (30-40% unchanged); Bile
  • Mechanism of Action: Inactivates bacterial ribosomal proteins

Antibiotic Sensitivities[4]

Group Organism Sensitivity
Gram PositiveStrep. Group A, B, C, GS
Strep. PneumoniaeS
Viridans strepX1
Strep. anginosus gpX1
Enterococcus faecalisS
Enterococcus faeciumS
Staph. EpidermidisX1
C. jeikeiumR
L. monocytogenesX1
Gram NegativesN. gonorrhoeaeS
N. meningitidisX1
Moraxella catarrhalisX1
H. influenzaeX1
E. coliS
Klebsiella spI
E. coli/Klebsiella ESBL+X1
E coli/Klebsiella KPC+R
Enterobacter sp, AmpC negI
Enterobacter sp, AmpC posI
Serratia spX1
Serratia marcescensR
Salmonella spS
Shigella spS
Proteus mirabilisX1
Proteus vulgarisR
Providencia sp.X1
Morganella sp.X1
Citrobacter freundiiX1
Citrobacter diversusX1
Citrobacter sp.X1
Aeromonas spX1
Acinetobacter sp.X1
Pseudomonas aeruginosaR
Burkholderia cepaciaR
Stenotrophomonas maltophiliaR
Yersinia enterocoliticaX1
Francisella tularensisX1
Brucella sp.X1
Legionella sp.X1
Pasteurella multocidaX1
Haemophilus ducreyiX1
Vibrio vulnificusX1
MiscChlamydophila spR
Mycoplasm pneumoniaeX1
Rickettsia spX1
Mycobacterium aviumX1
Bacteroides fragilisX1
Prevotella melaninogenicaX1
Clostridium difficileX1
Clostridium (not difficile)X1
Fusobacterium necrophorumX1
Peptostreptococcus sp.X1


  • S susceptible/sensitive (usually)
  • I intermediate (variably susceptible/resistant)
  • R resistant (or not effective clinically)
  • S+ synergistic with cell wall antibiotics
  • U sensitive for UTI only (non systemic infection)
  • X1 no data
  • X2 active in vitro, but not used clinically
  • X3 active in vitro, but not clinically effective for Group A strep pharyngitis or infections due to E. faecalis
  • X4 active in vitro, but not clinically effective for strep pneumonia


  1. Nitrofurantoin: Drug information. UpToDate. Accessed April 1, 2019.
  2. Nitrofurantoin: Drug information. UpToDate. Accessed April 1, 2019.
  3. Spring PJ, Sharpe DM, Hayes MW. Nitrofurantoin and peripheral neuropathy: A forgotten problem? Med J Aust 2001;174:153-4.
  4. Sanford Guide to Antimicrobial Therapy 2014
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