What is the recommended dosage of Macrodantin (nitrofurantoin) for an uncomplicated urinary tract infection (UTI)?

Macrodantin (Nitrofurantoin) Dosing for Uncomplicated UTI

For acute uncomplicated cystitis in adult women, prescribe nitrofurantoin 100 mg twice daily for 5 days. 1

Treatment Dosing Algorithm

First-Line Therapy Selection

• Nitrofurantoin is a recommended first-line agent for uncomplicated UTI in women, alongside TMP-SMX and fosfomycin, based on local antibiogram patterns. 1
• Nitrofurantoin should be prioritized as it causes less collateral damage to normal flora compared to fluoroquinolones and maintains excellent susceptibility rates (>95% of E. coli isolates remain susceptible). 1, 2

Specific Dosing Regimen

• Standard dose: 100 mg orally twice daily for 5 days for acute uncomplicated cystitis. 1
• This 5-day regimen has clear evidence supporting its efficacy and represents the optimal balance between clinical cure and minimizing antibiotic exposure. 1
• Alternative dosing of 100 mg four times daily for 3 days has been studied but lacks robust comparative evidence to support routine use over the 5-day twice-daily regimen. 3

Maximum Treatment Duration

• Do not exceed 7 days of treatment for acute cystitis episodes, even in recurrent UTI patients. 1
• Shorter courses are preferred to reduce antimicrobial resistance and adverse effects while maintaining efficacy. 1

Critical Contraindications and Limitations

When NOT to Use Nitrofurantoin

• Never use for pyelonephritis or complicated UTIs - nitrofurantoin achieves inadequate tissue concentrations outside the bladder. 4
• Contraindicated in renal impairment of any degree (CrCl <30-60 mL/min depending on guidelines) as inadequate urinary concentrations are achieved. 5
• Avoid in the third trimester of pregnancy due to risk of hemolytic anemia in the newborn. 5
• Do not use for febrile UTI or suspected upper tract involvement. 4

Clinical Efficacy Evidence

Symptomatic and Bacteriological Cure

• In bacteriologically proven UTI, nitrofurantoin achieves bacteriological cure in 81% of patients by day 3 versus 20% with placebo (NNT = 1.6). 3
• Symptomatic improvement occurs in 77% by day 3 in clinically suspected UTI versus 54% with placebo (NNT = 4.4). 3
• By day 7, symptomatic cure rates reach 88% with sustained bacteriological clearance. 3

Common Pitfalls to Avoid

Inappropriate Use Scenarios

• Do not prescribe for upper tract infections - this is the most common error, as nitrofurantoin only concentrates in urine, not renal parenchyma. 4
• Avoid using fluoroquinolones as first-line when nitrofurantoin is appropriate, as this drives unnecessary resistance (E. coli resistance to fluoroquinolones is ~24% versus 2.3% for nitrofurantoin). 2
• Do not extend treatment beyond 7 days for simple cystitis, as this increases adverse event risk without additional benefit. 1

Safety Monitoring

• While serious pulmonary or hepatic adverse events are extremely rare (0.001% and 0.0003% respectively), be aware they can occur, particularly with prolonged use. 4
• GI disturbances and rash are more common but generally mild and self-limited. 4