What is the recommended treatment and dosage for Methenamine (hexamine) in urinary tract infections?

Methenamine Treatment for Urinary Tract Infections

The recommended treatment for prevention of recurrent urinary tract infections (UTIs) is methenamine hippurate 1 gram twice daily (morning and night) for adults and children over 12 years of age, with treatment typically continuing for 6-12 months based on clinical response. 1, 2

Dosage Recommendations

• Adults and children >12 years: 1 gram twice daily (morning and night) 1, 2
• Children 6-12 years: 0.5 to 1 gram twice daily (morning and night) 2
• Treatment duration: 6-12 months based on clinical response 1

Mechanism and Efficacy

Methenamine hippurate works by converting to formaldehyde in acidic urine, which has antibacterial properties. Its effectiveness depends on maintaining proper urinary conditions:

• Urinary pH must be maintained below 6.0 for optimal effectiveness 1
• May require supplemental acidification if urinary pH is not naturally acidic 1, 2
• Efficacy should be monitored through repeated urine cultures 1, 2

Patient Selection

Methenamine hippurate is most appropriate for:

• Patients with normal urinary tract anatomy and function 1
• Women with recurrent UTIs 1
• Patients with intact bladder function 1
• Patients with long-term indwelling catheters or intermittent catheterization 1

It is less effective in:

• Patients with neuropathic bladder 1, 3
• Patients with renal tract abnormalities 1, 3

Treatment Algorithm

1. Confirm diagnosis of recurrent UTI (≥3 episodes per year)
2. Treat any active infection with appropriate antibiotics first 4
3. Verify patient has normal urinary tract anatomy and function
4. Start methenamine hippurate 1 g twice daily
5. Monitor urinary pH (should be <6.0)
6. Add urinary acidification if needed
7. Monitor for symptom improvement and adverse effects
8. Continue treatment for 6-12 months 1

Clinical Benefits

• Reduces number of UTI recurrences by approximately two-thirds 4, 5
• Longer time to UTI development (5.5 months vs 3.3 months before treatment) in older adults 1
• Lower risk of developing antimicrobial resistance compared to antibiotics 1, 6
• Generally well-tolerated with fewer adverse effects than antibiotics 1, 7

Important Considerations and Pitfalls

• Methenamine hippurate is primarily for UTI prevention, not treatment of active infections 4
• Effectiveness depends on maintaining acidic urine (pH <6.0) 1, 2
• Restrict alkalinizing foods and medications during treatment 2
• Treatment failure should be considered if symptoms persist beyond 7 days or recur within 6-8 weeks despite consistent use 1
• More effective in patients without renal tract abnormalities than in those with abnormalities 3
• The effect appears to be greater in patients with higher frequency of recurrent UTIs 5

Methenamine hippurate represents an antimicrobial-sparing alternative for UTI prevention with demonstrated effectiveness and minimal risk of developing bacterial resistance, making it particularly valuable in the era of increasing antibiotic resistance 1, 7.