Dosing and uses of Cystex (methenamine/sodium salicylate/benzoic acid)
Adult dosage forms and strengths
methenamine/sodium salicylate/benzoic acid
tablet
- 162mg/162.5mg/32mg
Urinary Tract Infection Prophylaxis
2 tablets PO q12hr
Administer with meals and at bedtime
Use only after eradication of UTI by other appropriate antibiotic
Methenamine: Indicated for prophylaxis/suppression for chronic recurring UTIs when long-term therapy is required
Sodium salicylate: Analgesic
Benzoic acid: Elicits weak antifungal and antibacterial properties; also helps acidify urine
Pediatric dosage forms and strengths
methenamine/sodium salicylate/benzoic acid
tablet
- 162mg/162.5mg/32mg
Urinary Tract Infection Prophylaxis
<16 years: Safety/efficacy not established
>16 years: 2 tablets PO q6hr
Administer with meals and at bedtime
Use only after eradication of UTI by other appropriate antibiotic
Methenamine: Indicated for prophylaxis/suppression for chronic recurring UTIs when long-term therapy is required
Sodium salicylate: Analgesic
Benzoic acid: Elicits weak antifungal and antibacterial properties; also helps acidify urine
Cystex (methenamine/sodium salicylate/benzoic acid) adverse (side) effects
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
Warnings
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 and lactation
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.
Pharmacology of Cystex (methenamine/sodium salicylate/benzoic acid)
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
