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  • 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




  • 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 Positive Strep. Group A, B, C, G S
Strep. Pneumoniae S
Viridans strep X1
Strep. anginosus gp X1
Enterococcus faecalis S
Enterococcus faecium S
Staph. Epidermidis X1
C. jeikeium R
L. monocytogenes X1
Gram Negatives N. gonorrhoeae S
N. meningitidis X1
Moraxella catarrhalis X1
H. influenzae X1
E. coli S
Klebsiella sp I
E. coli/Klebsiella ESBL+ X1
E coli/Klebsiella KPC+ R
Enterobacter sp, AmpC neg I
Enterobacter sp, AmpC pos I
Serratia sp X1
Serratia marcescens R
Salmonella sp S
Shigella sp S
Proteus mirabilis X1
Proteus vulgaris R
Providencia sp. X1
Morganella sp. X1
Citrobacter freundii X1
Citrobacter diversus X1
Citrobacter sp. X1
Aeromonas sp X1
Acinetobacter sp. X1
Pseudomonas aeruginosa R
Burkholderia cepacia R
Stenotrophomonas maltophilia R
Yersinia enterocolitica X1
Francisella tularensis X1
Brucella sp. X1
Legionella sp. X1
Pasteurella multocida X1
Haemophilus ducreyi X1
Vibrio vulnificus X1
Misc Chlamydophila sp R
Mycoplasm pneumoniae X1
Rickettsia sp X1
Mycobacterium avium X1
Anaerobes Actinomyces X1
Bacteroides fragilis X1
Prevotella melaninogenica X1
Clostridium difficile X1
Clostridium (not difficile) X1
Fusobacterium necrophorum X1
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

See Also


  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