Nitrofurantoin (Macrobid, Macrodantin)

KEY POINTS

Nitrofurantoin is an antibiotic used to treat or prevent urinary tract infections
Is reduced by bacterial flavoproteins to reactive intermediates that inactivate or alter bacterial ribosomal proteins. This leads to inhibition of protein synthesis, aerobic energy metabolism, DNA, RNA and cell wall synthesis.
- Bactericidal in urine at therapeutic doses
- E. coli (the most common bacteria to cause UTI) resistance is typically not as bad as that of with E. coli and ciprofloxacin or sulfamethoxazole-trimethoprim (Bactrim, SMX/TMP). This means nitrofurantoin may be a good choice for empiric therapy (i.e., when sensitivity is not known), but lower UTI is diagnosed and E. coli is suspected.
Is indicated for lower urinary tract infections (i.e., not for pyelonephritis) and is also not a good choice if concern for prostatitis is present
Dosing depends on the product
- Furadantin and Macrodantin are dosed 50-100mg every 6 hours
- Macrobid is dosed 100mg twice daily
  - Note: “BID” is in the name and it is twice daily
Generally avoid use in CrCl < 30 mL/min or elderly (>65 years old)
- Note: 60 mL/min was the previous cut-off, see link below: updated Beers Criteria 2015
- Poor kidney function will mean lower urinary concentrations and higher risk for toxicity
Is normally well tolerated, but repeated or long-term use has been associated with pulmonary toxicity
- Liver toxicity, optic neuritis, and peripheral neuropathy have been reported

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