methenamine/sodium acid phosphate (Rx)

Brand and Other Names:Uroquid-Acid No. 2, Utac
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

methenamine/sodium acid phosphate

tablet

  • 500 mg/500 mg
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Urinary Tract Infection Prophylaxis

Initial: 2 tablets PO q6hr with liberal fluid intake

Maintenance: 1-2 tablets PO q12hr

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 acid phosphate: Urinary acidifier

Safety/efficacy not established

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Interactions

Interaction Checker

and methenamine/sodium acid phosphate

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    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

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            Adverse Effects

            1-10%

            Dysuria

            Gastric upset

            Nausea

            Rash

            Frequency Not Defined

            Diarrhea

            Nausea

            Stomach pain

            Vomiting

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            Warnings

            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 >55 yr, hypovolemia, baseline kidney disease, bowel obstruction, active colitis, and those using medicines that affect renal perfusion or function (eg, 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 (ie, CrCl <30 mL/min)

            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 acid phosphate

            • History of gastrointestinal pain
            • Sodium restriction
            • History of kidney stones
            • Risk of acute phosphate nephropathy
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            Pregnancy & 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.

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            Pharmacology

            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%)

            Sodium Acid Phosphate

            Onset: 1-3 hr

            Duration: 1-3 hr

            Bioavailability: 66%

            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 acid phosphate: Urinary acidifier; elicits osmotic effect in GI tract

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            Formulary

            FormularyPatient Discounts

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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
            3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
            4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
            PA Prior Authorization
            Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
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            Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
            ST Step Therapy
            Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
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