methenamine

REMS

Prophylaxis of frequently recurring urinary tract infections when long-term therapy is considered necessary.

Action ⬆ ⬇

Hydrolyzed to formaldehyde (has bactericidal effects) and ammonia in acidic urine. Other components, hippuric acid or mandelic acid, help maintain urine acidity and suppress bacterial growth.

Therapeutic effects:

Reduction in frequency of urinary tract infections.

Pharmacokinetics ⬆ ⬇

Absorption: Rapidly absorbed.

Distribution: Concentrated in the urine.

Metabolism/Excretion: Hydrolyzed to formaldehyde and ammonia in the urine. Primarily excreted in the urine (70–90% as unchanged drug).

Half-Life: 4 hr.

Time/Action Profile ⬆ ⬇

(plasma concentrations)

ROUTE	ONSET	PEAK	DURATION
PO	unknown	1–2 hr	12 hr

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Renal impairment;
Severe hepatic impairment;
Severe dehydration;
Concurrent use of sulfonamides.
Lactation: Lactation.

Use Cautiously in:

Aspirin hypersensitivity (contains tartrazine);
OB: Safety not established in pregnancy;
Pedi: Children <6 yr (safety and effectiveness not established).

Adv. Reactions/Side Effects ⬆ ⬇

Derm: rash

GU: dysuria

GI: ↑liver enzymes, dyspepsia, nausea

Interactions ⬆ ⬇

Drug-drug:

Use with sulfonamides, including glyburide, glipizide, or glimepiride, may form an insoluble precipitate with formaldehyde in urine; concurrent use contraindicated.

Route/Dosage ⬆ ⬇

PO (Adults and Children >12 yr): 1000 mg twice daily.
PO (Children 6–12 yr): 500–1000 mg twice daily

Availability ⬆ ⬇

(Generic available)

Tablets: 1000 mg

Assessment ⬆ ⬇

Monitor for signs/symptoms of urinary tract infection (fever, dysuria, urinating urgency and frequency, suprapubic pain).
Monitor urinary output. Assess for hematuria.

Lab Test Considerations:

Evaluate BUN, serum creatinine, AST, and ALT.
Monitor urine pH periodically during therapy.

Implementation ⬆ ⬇

PO: Administer with food to minimize GI upset. Administer with cranberry juice, ascorbic acid, or ammonium chloride to acidify urine; avoid intake of alkalinizing agents (sodium bicarbonate, antacids).

Patient/Family Teaching ⬆ ⬇

Explain purpose and side effects of medication to patient. Advise patient to read Patient Information before starting therapy.
Advise patient to notify health care provider of all Rx or OTC medications, vitamins, or herbal products being taken and to consult health care provider before taking other medications.
Educate patient to drink plenty of fluids to ensure adequate urine flow.
Instruct patient to avoid foods/diets that alkalinize urine, such as milk and citrus fruits.
Advise patient to notify health care provider immediately if painful urination or blood in the urine occurs.
Rep: Advise women of reproductive potential to notify health care provider if pregnancy is planned or suspected or if breastfeeding.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇