Methenamine/Sodium Acid Phosphate

Reviewed on 8/27/2021

What Is Methenamine/Sodium Acid Phosphate and How Does It Work?

Methenamine/sodium acid phosphate is used for urinary tract infection (UTI) prophylaxis.

Methenamine/sodium acid phosphate is available under the following different brand names: Uroquid-Acid No. 2 and Utac.

What Are the Dosages of Methenamine/Sodium Acid Phosphate?

Dosages of Methenamine/Sodium Acid Phosphate:

Dosage Forms and Strengths

Tablet

  • 500 mg/500 mg

Dosage Considerations – Should be Given as Follows:

Urinary Tract Infection (UTI) Prophylaxis

  • Initial: 2 tablets orally every 6 hours with liberal fluid intake
  • Maintenance: 1-2 tablets orally every 12 hours
  • Use only after eradication of UTI by another appropriate antibiotic
    • Methenamine: Indicated for prophylaxis/suppression for chronic recurring UTIs when long-term therapy is required
    • Sodium acid phosphate: Urinary acidifier

Safety/efficacy not established in pediatric patients

What Are Side Effects Associated with Using Methenamine/Sodium Acid Phosphate?

Common side effects of methenamine/sodium acid phosphate include:

  • Pain, discomfort, or burning when urinating
  • Gastric upset
  • Nausea
  • Rash

Other side effects of methenamine/sodium acid phosphate include:

  • Diarrhea
  • Nausea
  • Stomach pain
  • Vomiting

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Methenamine/Sodium Acid Phosphate?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

  • Methenamine/sodium acid phosphate has no listed severe interactions with other drugs.
  • Methenamine/sodium acid phosphate has no listed serious interactions with other drugs.
  • Methenamine/sodium acid phosphate has no listed moderate interactions with other drugs.
  • Methenamine/sodium acid phosphate has no listed mild interactions with other drugs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

SLIDESHOW

Urinary Incontinence in Women: Types, Causes, and Treatments for Bladder Control See Slideshow

What Are Warnings and Precautions for Methenamine/Sodium Acid Phosphate?

Warnings

  • This medication contains methenamine/sodium acid phosphate. Do not take Uroquid-Acid No. 2 or Utac if you are allergic to methenamine/sodium acid phosphate or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Black Box Warnings

Sodium acid phosphate

  • Rare reports of acute phosphate nephropathy with oral sodium phosphate products used for colon cleansing before colonoscopy
  • Some cases have resulted in permanent renal function impairment requiring long-term hemodialysis
  • Risk factors for acute phosphate nephropathy include age over 55 years, hypovolemia, baseline kidney disease, bowel obstruction, active colitis, and those using medicines that affect renal perfusion or function (e.g., diuretics, ACE inhibitors, ARBs, NSAIDs)
  • Carefully follow dosing regimen as recommended (pm/am split dose) with adequate hydration

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 acid phosphate
  • Hypersensitivity
  • Addison's disease
  • Hyperphosphatemia
  • Acidification of urine in urinary stone disease
  • Urolithiasis or struvite stone formation
  • Severe renal impairment (i.e., CrCl less than 30 mL/minute)

Effects of Drug Abuse

  • No information is available

Short-Term Effects

  • See "What Are Side Effects Associated with Using Methenamine/Sodium Acid Phosphate?”

Long-Term Effects

  • See "What Are Side Effects Associated with Using Methenamine/Sodium Acid Phosphate?”

Cautions

  • Methenamine
  • Large doses may cause bladder irritation, urinary frequency, albuminuria, and hematuria
  • Maintain acidic pH of urine, especially when treating urea-splitting organisms (e.g., Proteus, Pseudomonas)
  • Monitor liver function tests, especially with a history of liver impairment
  • Safe use is not established during pregnancy, especially 1st and 2nd trimester
  • May precipitate uric acid stones in patients with gout
  • Sodium acid phosphate
  • History of gastrointestinal pain
  • Sodium restriction
  • History of kidney stones
  • Risk of acute phosphate nephropathy

Pregnancy and Lactation

  • Use methenamine/sodium acid phosphate with caution during pregnancy if the benefits outweigh the risks. Animal studies show risk and human studies are not available or neither animal nor human studies were done.
  • Methenamine is excreted in human milk. Caution is advised while breastfeeding. The risk to infants cannot be ruled out. Consult your doctor.
References
https://reference.medscape.com/drug/uroquid-acid-no-2-utac-methenamine-sodium-acid-phosphate-999453

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