Yes

Antibiotic, Miscellaneous

Prophylaxis or suppression of recurrent urinary tract infections; urinary tract discomfort secondary to hypermotility

C

Severe dehydration, renal insufficiency, hepatic insufficiency in patients receiving hippurate salt, hypersensitivity to methenamine or any component; patients receiving sulfonamides

Use with caution in patients with hepatic disease, gout, and the elderly; doses of 8 g/day for 3-4 weeks may cause bladder irritation, some products may contain tartrazine; methenamine should not be used to treat infections outside of the lower urinary tract. Use care to maintain an acid pH of the urine, especially when treating infections due to urea splitting organisms (eg, Proteus and strains of Pseudomonas); reversible increases in LFTs have occurred during therapy especially in patients with hepatic dysfunction.

1% to 10%:

Dermatologic: Rash (3.5%)

Gastrointestinal: Nausea, dyspepsia (3.5%)

Genitourinary: Dysuria (3.5%)

<1%: Bladder irritation, crystalluria (especially with large doses), increased AST/ALT (reversible, rare)

Well tolerated; treatment includes GI decontamination, if possible, and supportive care

Decreased effect: Sodium bicarbonate and acetazolamide will decrease effect secondary to alkalinization of urine

Increased toxicity: Sulfonamides (may precipitate)

Protect from excessive heat

Methenamine is hydrolyzed to formaldehyde and ammonia in acidic urine; formaldehyde has nonspecific bactericidal action

Absorption: Readily absorbed from GI tract

Metabolism: 10% to 30% of the drug will be hydrolyzed by gastric juices unless it is protected by an enteric coating; ~10% to 25% is metabolized in the liver

Half-life: 3-6 hours

Elimination: Occurs via glomerular filtration and tubular secretion with ~70% to 90% of dose excreted unchanged in urine within 24 hours

Oral:

<6 years: 0.25 g/30 lb 4 times/day

6-12 years:

Hippurate: 25-50 mg/kg/day divided every 12 hours or 0.5-1 g twice daily

Mandelate: 50-75 mg/kg/day divided every 6 hours or 0.5 g 4 times/day

Children >12 years and Adults:

Hippurate: 1 g twice daily

Mandelate: 1 g 4 times/day after meals and at bedtime

Dosing adjustment/comments in renal impairment: Cl_cr <50 mL/minute: Avoid use

Foods/diets which alkalinize urine pH >5.5 decrease activity of methenamine; cranberry juice can be used to acidify urine and increase activity of methenamine

Urinalysis, periodic liver function tests in patients

catecholamines and VMA (U); HIAA (U)

None reported

None reported

No information available to require special precautions

No effects or complications reported

Take per recommended schedule, at regular intervals around-the-clock. Complete full course of therapy; do not skip doses. Maintain adequate hydration (2-3 L/day of fluids unless instructed to restrict fluid intake). Avoid excessive citrus fruits, milk, or alkalizing medications. You may experience nausea or vomiting or GI upset (small frequent meals, frequent mouth care, sucking lozenges, or chewing gum may help). Report pain on urination or blood in urine, skin rash, other persistent adverse effects, or if condition does not improve. Pregnancy precautions: Inform prescriber if you are or intend to be pregnant.

Urine should be acidic (pH <5.5) for maximum effect

Suspension, oral: 0.5 g/5 mL (480 mL)

Tablet, as hippurate (Hiprex®, Urex®): 1 g (Hiprex® contains tartrazine dye)

Tablet, as mandelate, enteric coated: 500 mg, 1 g

Vainrub B and Musher DM, "Lack of Effect of Methenamine in Suppression of, or Prophylaxis Against, Chronic Urinary Tract Infection," Antimicrob Agents Chemother, 1977, 12:625-9.