Generic Name

Methenamine Hippurate

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Classification

FDA Approved Indications

• Prevention of recurrent urinary tract infections in patients with chronic cystitis

Mechanism of Action

Methenamine Hippurate is converted in acidic urine to formaldehyde, which denatures bacterial proteins and acts as a bactericidal agent, preventing bacterial growth in the urinary tract.

Dosage and Administration

Adult: 500 mg to 1 g orally twice daily, preferably after meals and at bedtime

Pediatric: Not typically used in children; consult pediatric guidelines

Geriatric: Adjust dose based on renal function; monitor closely due to potential renal impairment

Renal Impairment: Dosage adjustment recommended; avoid use if urine pH is above 6.0

Hepatic Impairment: Use with caution; hepatic function should be considered

Pharmacokinetics

Absorption: Well absorbed from gastrointestinal tract

Distribution: Distributed mainly in urine, penetrating the urinary tract

Metabolism: Unchanged in urine; some metabolism to formaldehyde and ammonia analogs occurs in bacteria

Excretion: Excreted primarily via urine

Half Life: Approximately 1.5-2 hours in healthy individuals

Contraindications

• Urinary alkalinity (pH >6.0)
• Severe renal impairment
• Hepatic impairment
• Known hypersensitivity

Precautions

• Use caution in patients with impaired renal or hepatic function; monitor renal function regularly.
• Not recommended during pregnancy unless benefits outweigh risks.
• Avoid in patients with risk factors for urinary retention or obstruction.

Adverse Reactions - Common

• Gastrointestinal upset (nausea, vomiting) (Common)
• Dizziness (Less common)

Adverse Reactions - Serious

• Urinary obstruction due to crystalluria (Rare)
• Hemolytic anemia (with G6PD deficiency) (Rare)
• Allergic reactions, including rash or hypersensitivity (Rare)

Drug-Drug Interactions

• Urinary acidifiers (e.g., ammonium chloride) may enhance formaldehyde formation and increase toxicity.

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Take medication exactly as prescribed, after meals.
• Maintain adequate hydration to minimize crystalluria.
• Report signs of urinary obstruction—such as difficulty urinating, lower abdominal pain.
• Follow-up urine tests as scheduled.

Special Considerations

Black Box Warnings:

• Use with caution in patients with renal impairment due to risk of crystalluria and urinary obstruction.

Genetic Factors: G6PD deficiency may predispose to hemolytic anemia.

Lab Test Interference: May cause false-positive results for urinary glucose using some test methods.

Overdose Management

Signs/Symptoms: Nausea, vomiting, urinary crystalluria, hematuria, signs of systemic formaldehyde toxicity.

Treatment: Discontinue medication immediately. Supportive care; hemodialysis may be considered in severe cases of systemic toxicity.

Storage and Handling

Storage: Store at controlled room temperature, away from moisture and light.

Stability: Stable for at least 2 years when stored properly.