Does primary care prescribe methenamine hippurate (MH) 1gm for urinary tract infections?

Methenamine Hippurate in Primary Care for Urinary Tract Infections

Primary care physicians can prescribe methenamine hippurate 1g for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary, but it should only be used after eradication of the infection by other appropriate antimicrobial agents. 1

Indications and Usage

• Methenamine hippurate is indicated for prophylactic or suppressive treatment of frequently recurring UTIs when long-term therapy is needed 1
• It should only be used after the initial infection has been eradicated by other appropriate antimicrobial agents 1
• Methenamine hippurate works by hydrolyzing to formaldehyde in acidic urine, providing antibacterial activity against common UTI pathogens such as E. coli, enterococci, and staphylococci 1

Evidence for Effectiveness

• Methenamine hippurate may be considered for the reduction of catheter-associated bacteriuria and UTI in patients after gynecologic surgical procedures who are catheterized for no more than 1 week (C-I level evidence) 2
• In a Finnish study (n=290), methenamine hippurate 1g showed a recurrence rate of 34.2% compared to 63.2% in placebo, though it was less effective than trimethoprim (10.4%) 2
• A Swedish study demonstrated that methenamine hippurate 1g twice daily reduced UTIs by 73% compared to placebo (p<0.01) 2
• Recent evidence suggests methenamine hippurate is non-inferior to daily antibiotic prophylaxis for preventing recurrent UTIs in women (RR 1.15; 95%CI 0.96-1.38) 3

Administration Guidelines

• The standard dosage is 1g twice daily 1
• When using methenamine hippurate to reduce UTIs, urinary pH should be maintained below 6.0 (B-III level evidence) 2
• Over 90% of the methenamine component is excreted in the urine within 24 hours after administration 1
• Antibacterial activity is demonstrable in urine within 30 minutes after ingestion 1

Limitations and Contraindications

• Methenamine hippurate should not be used routinely to reduce catheter-associated bacteriuria or UTI in patients with long-term intermittent (A-II) or long-term indwelling urethral or suprapubic (A-III) catheterization 2
• It has limited value for treating established infections; it achieved abacteriuria in only 6 of 14 patients with active infections in one study 4
• The urine must be kept sufficiently acidic for effectiveness against urea-splitting organisms such as Proteus and Pseudomonas 1

Safety Profile

• Methenamine hippurate is generally well-tolerated with few adverse effects 5
• In a study of renal transplant recipients, only 2 out of 38 patients reported adverse effects (one with nausea and one with general intolerance) 5
• No development of urinary calculi or deterioration of renal function was observed in long-term treatment (average 16 months) 4
• It may offer advantages over antibiotics in terms of antimicrobial resistance; one study showed lower rates of antibiotic resistance in E. coli from perineal swabs in patients taking methenamine hippurate (56%) compared to those on daily antibiotics (72%) (p=0.05) 6

Follow-up Recommendations

• Patients should seek immediate medical attention if symptoms do not resolve within 4 weeks after treatment completion or recur within 2 weeks 7
• For patients whose symptoms do not resolve by the end of treatment or recur within 2 weeks, a urine culture with antimicrobial susceptibility testing should be performed 7
• Routine post-treatment urinalysis or urine cultures are NOT indicated for asymptomatic patients 7

Clinical Pearls and Pitfalls

• Methenamine hippurate is most effective as prophylaxis after achieving abacteriuria with appropriate antibiotics rather than as primary treatment for active infections 4
• Maintaining acidic urine is crucial for effectiveness, but data are insufficient to recommend the best method to achieve low urinary pH 2
• Studies of ascorbic acid in dosages up to 4g per day have shown no significant effect on mean urinary pH; dosages as high as 12g per day may be required 2
• The hippurate component helps maintain urine acidity and also has some antibacterial activity 1