methenamine (Rx)

Brand and Other Names:Hiprex, Urex
  • Print

Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

oral solution

  • 500mg/5mL

tablet, hippurate

  • 1g

tablet, mandelate

  • 500mg
  • 1g

Urinary Tract Infection Prophylaxis

Indicated for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary

Methenamine hippurate: 1 g PO q12hr

Methenamine mandelate: 1 g PO q6hr

Dosing Considerations

Dose selection for an elderly patient should be cautious, usually starting at low end of dosing range, reflecting greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy

Dosage Forms & Strengths

oral solution

  • 500 mg/5mL

tablet, hippurate

  • 1g

tablet, mandelate

  • 500mg
  • 1g

Urinary Tract Infection Prophylaxis

Indicated for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary

Methenamine hippurate

  • <6 years: Safety and efficacy not established
  • 6-12 years: 0.5-1 g PO q12hr
  • >12 years: 1 g PO q12hr

Methenamine mandelate

  • <6 years: 18.4 mg/kg PO q6hr
  • 6-12 years: 0.5-1 g PO q6hr
  • >12 years: 1 g PO q6hr
Next:

Interactions

Interaction Checker

and methenamine

No Results

     activity indicator 
    No Interactions Found
    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

            All Interactions Sort By:
             activity indicator 

            Contraindicated (0)

              Serious - Use Alternative (5)

              • acetazolamide

                acetazolamide, methenamine. Other (see comment). Contraindicated. Comment: This combination may form an insoluble precipitate in the urine, decreasing the effects of both agents.

              • cholera vaccine

                methenamine, cholera vaccine. pharmacodynamic antagonism. Avoid or Use Alternate Drug. Avoid coadministration of cholera vaccine with systemic antibiotics since these agents may be active against the vaccine strain. Do not administer cholera vaccine to patients who have received oral or parenteral antibiotics within 14 days prior to vaccination.

              • sulfadiazine

                methenamine, sulfadiazine. Other (see comment). Contraindicated. Comment: This combination may form an insoluble precipitate in the urine, decreasing the effects of both agents.

              • sulfamethoxazole

                methenamine, sulfamethoxazole. Other (see comment). Contraindicated. Comment: This combination may form an insoluble precipitate in the urine, decreasing the effects of both agents.

              • sulfisoxazole

                methenamine, sulfisoxazole. Other (see comment). Contraindicated. Comment: This combination may form an insoluble precipitate in the urine, decreasing the effects of both agents.

              Monitor Closely (2)

              • pseudoephedrine

                methenamine decreases effects of pseudoephedrine by unknown mechanism. Use Caution/Monitor. Urinary excretion of indirect acting alpha/beta agonists (eg, pseudoephedrine) may increase when administered concomitantly with urinary acidifying agents, resulting in lower serum concentrations.

              • sodium picosulfate/magnesium oxide/anhydrous citric acid

                methenamine decreases effects of sodium picosulfate/magnesium oxide/anhydrous citric acid by altering metabolism. Use Caution/Monitor. Coadministration with antibiotics decreases efficacy by altering colonic bacterial flora needed to convert sodium picosulfate to active drug.

              Minor (0)

                Previous
                Next:

                Adverse Effects

                To report suspected adverse reactions, contact Validus Pharmaceuticals LLC at 1-866-982-5438 (1-866-9VALIDUS) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch

                1-10%

                Dysuria

                Gastric upset

                Nausea

                Rash

                Previous
                Next:

                Warnings

                Contraindications

                Hypersensitivity to methenamine or tartrazine (FD&C Yellow No. 5)

                Severe renal or hepatic insufficiency

                Concurrent sulfonamides or acetazolamide may form insoluble precipitate in urine

                Cautions

                Patients with pre-existing hepatic insufficiency may suffer adverse effects from the small amounts of ammonia and formaldehyde that are produced; the classical syndrome of acute hepatic failure may be evoked in these patients

                Taking therapy in absence of proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to patient and increases risk of development of drug-resistant bacteria

                Large doses of methenamine (8 g daily for 3 to 4 weeks) have caused bladder irritation, painful and frequent micturition, albuminuria, and gross hematuria

                Maintain acidic pH of urine, especially when treating urea-splitting organisms, e.g. Proteus, Pseudomonas

                Monitor LFTs, especially in patients 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

                Previous
                Next:

                Pregnancy & Lactation

                Pregnancy Category: C

                Lactation: excreted in breast milk; no adverse effects documented

                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.

                Previous
                Next:

                Pharmacology

                Mechanism of Action

                Methenamine hydrolyzes to ammonia and formaldehyde (nonspecific antibacterial) in acidic urine

                Mandelic acid or hippuric acid acidify the urine

                Pharmacokinetics

                Half-life: 4.3 hr

                Onset: 30 min

                Peak plasma time: 3-8 hr

                Vd: 0.56 L/kg

                Excretion: urine; methenamine 90% excreted w/in 24 hr; mandelic or hippuric acid may accumulate with severe renal impairment

                Previous
                Next:

                Images

                No images available for this drug.
                Previous
                Next:

                Patient Handout

                A Patient Handout is not currently available for this monograph.
                Previous
                Next:

                Formulary

                FormularyPatient Discounts

                Adding plans allows you to compare formulary status to other drugs in the same class.

                To view formulary information first create a list of plans. Your list will be saved and can be edited at any time.

                Adding plans allows you to:

                • View the formulary and any restrictions for each plan.
                • Manage and view all your plans together – even plans in different states.
                • Compare formulary status to other drugs in the same class.
                • Access your plan list on any device – mobile or desktop.

                The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

                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.
                QL Quantity Limits
                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.
                OR Other Restrictions
                Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.
                Additional Offers
                Email to Patient

                From:

                To:

                The recipient will receive more details and instructions to access this offer.

                By clicking send, you acknowledge that you have permission to email the recipient with this information.

                Email Forms to Patient

                From:

                To:

                The recipient will receive more details and instructions to access this offer.

                By clicking send, you acknowledge that you have permission to email the recipient with this information.

                Previous
                Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.