methenamine/sodium salicylate/benzoic acid (OTC)

1-10%

Methenamine

• Dysuria
• Gastric upset
• Nausea
• Rash

Frequency Not Defined

Sodium salicylate

• Angioedema
• Bronchospasm
• CNS alteration
• Dermatologic problems
• GI pain/ulceration/bleeding
• Hepatotoxicity
• Hearing loss

Contraindications

Methenamine

• Hypersensitivity to methenamine or tartrazine (FD&C Yellow No. 5)
• Renal or severe hepatic insufficiency
• Concurrent sulfonamides or acetazolamide may form insoluble precipitate in urine

Sodium Salicylate

• Hypersensitivity to aspirin or NSAIDs
• Bleeding gastrointestinal ulcers
• Asthma, Nasal polyps associated with asthma
• Hemolytic anemia from PK & G6PD deficiency
• Hemophilia
• Hemorrhagic diathesis
• Hemorrhoids, Lactating women, Sarcoidosis, Thrombocytopenia, Ulcerative colitis

Cautions

Methenamine

• Large doses may cause bladder irritation, urinary frequency, albuminuria, and hematuria
• Maintain acidic pH of urine, especially when treating urea-splitting organisms (eg, Proteus, Pseudomonas)
• Monitor LFTs, especially with history of liver impairment
• Safe use not established during pregnancy, especially 1st and 2nd trimester
• May precipitate uric acid stones in patients with gout

Sodium Salicylate

• Anemia
• GI malabsorption
• History of peptic ulcers
• Gout
• Hepatic disease
• Hypochlorhydria, Hypoprothrombinemia, Renal impairment, Renal calculi, Thyrotoxicosis, Vitamin K deficiency

Pregnancy Category: C

Lactation: methenamine is excreted in human milk; caution advised, risk to infant cannot be ruled out

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Methenamine

Half-Life: 3-6 hr

Absorption: well absorbed; 10-30% hydrolyzed by gastric acid unless enteric coated tablet

Peak Urine Time: (formaldehyde) 2 hr for hippurate salt, 3-8 hr for mandelate salt

Metabolism: by liver (10-25%)

Excretion: urine (90%)

Mechanism of Action

Methenamine: Hydrolyzed in acidic urine to ammonia and formaldehyde, which are bactericidal agents; does not convert to formaldehyde in serum.

Sodium salicylate: Analgesic

Benzoic acid: Elicits weak antifungal and antibacterial properties; also helps acidify urine