Methenamine Mandelate Tablets

Generic name:

Methenamine mandelate

Drug class:

Urinary tract antiseptic/antibacterial

Dosage form:

Tablets (1 g)

Root of administration:

Oral

Dose:

Adults: 1 g orally twice daily with meals. Pediatrics: 30 mg/kg/day in divided doses (up to 1 g/day). Dose may vary by indication; consult label.

Mechanism of action:

In acidic urine (pH <6), methenamine hydrolyzes to formaldehyde and ammonia; formaldehyde exerts bactericidal activity by denaturing bacterial proteins. Mandelate salt helps maintain acidic urine to promote conversion.

Drug usage cases:

• Prophylaxis of recurrent urinary tract infections (UTIs)
• Chronic suppression of bacteriuria in patients with structural or functional urinary tract abnormalities
• Prevention of catheter-associated UTIs (off-label)
• Suppression of UTIs in spinal cord injury or neurogenic bladder (off-label)
• Intermittent self-catheterization–associated UTI prophylaxis (off-label)

Drug contra indications:

• Renal impairment (CrCl <30 mL/min)
• Severe hepatic insufficiency
• Known hypersensitivity to methenamine or mandelic acid
• Urinary retention or obstruction
• Dehydration

Side effects:

• Gastrointestinal: nausea, vomiting, diarrhea, abdominal cramps
• Neurologic: headache
• Dermatologic: rash, urticaria
• Genitourinary: dysuria, bladder irritation
• Metabolic: electrolyte disturbances
• Hypersensitivity reactions including anaphylaxis (rare)

Warnings:

• Requires acidic urine (pH <6) for efficacy; alkalinizing agents reduce effectiveness
• Assess renal and hepatic function before and periodically during therapy
• Avoid in patients with significant renal or hepatic dysfunction
• Use caution in elderly or debilitated patients
• May interfere with urinary lab tests (e.g., ketones, bilirubin)
• Not effective for acute symptomatic UTIs

Use during pregnancy or breastfeeding:

Pregnancy: Category C. Animal studies demonstrate adverse fetal effects at high doses; human data are limited. Use only if potential benefit justifies potential risk.

Breastfeeding: Methenamine and its metabolites are excreted in breast milk. Potential risk to nursing infant is unknown; monitor infant for gastrointestinal disturbances. Use only if benefits outweigh risks.