Drug Index


Mechanism :

Methenamine is a urinary anti-infective medicine. Methenamine fights bacteria in the urine and bladder.
Methenamine may be used to treat and prevent urinary tract infections.

Indication :

  • Urinary tract infection prophylaxis. (Once it enters the body, it gets decomposed in acidic urine to form formaldehyde which destroys all bacteria. It has no antimicrobial activity in blood and tissues).

Contraindications :

Patient may not be able to take methenamine or may require a dosage adjustment or special monitoring during treatment if he has liver problems; renal failure. Methenamine is in the FDA pregnancy category C. This means that it is not known whether it will be harmful to an unborn baby. Methenamine passes into breast milk and may affect a nursing baby.

Dosing :

Methenamine Hippurate:
6-12 years:
0.5-1 g every 12 hours; maximum dose: 4 g/day.
>12 years and adults:
1 g twice to 4 times daily.
Methenamine mandelate:
<6 years:
18.4 mg/kg every 6 hours.
6-12 years:
0.5-1 g every 6 hours.
>12 years:
1 g every 6 hours.

Adverse Effect :

Gastritis, chemical cystitis, hematuria, dysuria, nausea and decreased appetite, skin rash.

Interaction :

Methenamine should not be taken if the following drugs are being used:
Carbonic anhydrase inhibitor such as Acetazolamide, Dichlorphenamide or Methazolamide;
Sulfa product such as Sulfadiazine, Sulfamethoxazole, Sulfasalazine; Diuretic.

Renal Dose :

Dose in Renal Impairment GFR (mL/min)
20-50Dose as in normal renal function
10-20Dose as in normal renal function

Dose in Patients undergoing Renal Replacement Therapies
CAPDUnknown dialysability. Avoid.
HDUnknown dialysability. Avoid.
HDF/High fluxUnknown dialysability. Avoid.
CAV/VVHDUnknown dialysability. Dose as in normal renal function

Hepatic Dose :

Dosage adjustments may be needed in mild and moderate hepatic impairment. It is contraindicated (methenamine hippurate and methenamine mandelate) in patients with severe hepatic disease.
03/24/2024 12:07:31 Methenamine
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