What class of antibiotic is Macrobid (nitrofurantoin)?

Macrobid (Nitrofurantoin) Antibiotic Classification

Macrobid is a nitrofuran derivative antibiotic, specifically containing nitrofurantoin in a macrocrystalline formulation. 1, 2

Drug Class Details

• Nitrofurantoin belongs to the nitrofuran class of antimicrobials, which are synthetic antibacterial agents that have been used for over 60 years in clinical practice 3, 4

• The nitrofuran derivatives work through a unique mechanism that involves multiple bacterial enzyme systems, making them effective against both Gram-positive and Gram-negative organisms commonly causing urinary tract infections 5, 6

Clinical Significance of This Drug Class

• Nitrofurans are bactericidal antibiotics that achieve high concentrations specifically in urine, which is why they are relegated to urinary tract infection treatment only 2, 6

• This class does not achieve therapeutic blood concentrations when administered orally, which is a critical limitation—nitrofurantoin should never be used for systemic infections, bacteremia, or pyelonephritis 6, 1

Spectrum of Activity

• Nitrofurantoin maintains excellent activity against common uropathogens including Escherichia coli, Staphylococcus saprophyticus, and Enterococcus species, with minimal resistance development despite decades of use 3, 4

• The drug is particularly valuable because resistance rates remain low compared to other antibiotic classes like fluoroquinolones and trimethoprim-sulfamethoxazole, which have experienced significant resistance increases 3, 4

Important Prescribing Caveat

• Nitrofurantoin is absolutely contraindicated in patients with creatinine clearance <60 mL/min because inadequate urinary drug concentrations prevent bactericidal activity and increase toxicity risk 2, 7