What is the recommended dosing of Macrobid (nitrofurantoin) for urinary tract infection (UTI) prophylaxis after intercourse in a young to middle-aged adult, possibly female, with a history of recurrent UTIs and impaired renal function?

Macrobid Dosing for Post-Coital UTI Prophylaxis

For post-coital UTI prophylaxis, take nitrofurantoin 50-100 mg as a single dose within 2 hours after sexual intercourse. 1

Specific Dosing Recommendations

The recommended dose is nitrofurantoin 50 mg taken as a single dose after intercourse, which is the preferred regimen based on guideline recommendations for post-coital prophylaxis. 1 This approach has been shown to be effective and safe, with significant reduction in recurrence rates compared to no prophylaxis. 1

Alternative Dosing Options

• Nitrofurantoin 100 mg can also be used as a single post-coital dose if the 50 mg dose is insufficient. 2
• The medication can be taken either before or after sexual intercourse, though within 2 hours of intercourse is the standard recommendation. 1, 2

Duration and Monitoring

• Continue prophylaxis for 6-12 months as this is the evidence-based duration that has been most extensively studied. 1, 2
• Periodic assessment and monitoring should occur during the prophylactic period. 1
• Some patients may continue for years if maintaining benefit without adverse events, though this is not evidence-based. 1

Critical Contraindications - MUST VERIFY

Do not use nitrofurantoin if creatinine clearance is <60 mL/min due to inadequate urinary drug concentrations and increased toxicity risk. 2 This is particularly important given the context mentions impaired renal function - you must verify renal function before prescribing.

Other Absolute Contraindications

• Last trimester of pregnancy 2
• Infants under 4 months of age 2
• Patients on dialysis 2

Pre-Treatment Requirements

Confirm eradication of any active UTI with a negative urine culture 1-2 weeks after treatment before initiating prophylaxis. 2 Starting prophylaxis with an active infection present will lead to treatment failure.

Advantages of Post-Coital Dosing

• Intermittent dosing is associated with decreased risk of adverse events including gastrointestinal symptoms and vaginitis compared to daily prophylaxis. 1
• This approach specifically targets women whose UTIs are temporally related to sexual activity. 1
• Post-coital prophylaxis uses less total antibiotic exposure than daily prophylaxis while maintaining efficacy. 3

Safety Profile

• Pulmonary toxicity risk: 0.001% 1, 2
• Hepatic toxicity risk: 0.0003% 1, 2
• Common adverse effects include gastrointestinal disturbances and skin rash. 1
• Serious adverse events are extremely rare with intermittent post-coital dosing. 3

Alternative Antibiotics if Nitrofurantoin Contraindicated

If nitrofurantoin cannot be used due to renal impairment or other contraindications:

• Trimethoprim-sulfamethoxazole 40/200 mg as a single post-coital dose 1
• Trimethoprim 100 mg as a single post-coital dose 1
• Fluoroquinolones and cephalosporins should be avoided as first-line options due to antimicrobial stewardship concerns. 1

Important Clinical Pitfalls

• Do not use nitrofurantoin for acute pyelonephritis or febrile UTIs - it does not achieve adequate tissue concentrations. 2
• Antibiotic choice should consider the patient's prior organism susceptibility profiles from previous urine cultures. 1, 2
• Rotating antibiotics at 3-month intervals can be considered to avoid selection of antimicrobial resistance if using continuous rather than post-coital prophylaxis. 1
• The prophylactic effect lasts only during active intake - UTI recurrence rates return to baseline after cessation. 1

Non-Antibiotic Alternatives

If the patient desires to avoid antibiotics or has contraindications:

• Methenamine hippurate can be considered as a non-antibiotic alternative. 1
• Lactobacillus-containing probiotics may be offered. 1
• Cranberry products may reduce recurrence but evidence quality is low. 1