Dosing and uses of Hiprex, Mandelamine (methenamine)
Adult dosage forms and strengths
oral solution
- 500mg/5mL
tablet, hippurate
- 1g
tablet, mandelate
- 500mg
- 1g
tablet, over the counter
- 162mg methenamine/162.5mg salicylic acid
Methenamine Hippurate
1 g PO q12hr
Methenamine Mandelate
1 g PO q6hr
Administration
Mandelate: With meals and at bedtime
Over the counter products: Follow directions on labeL
Other Indications & Uses
Methenamine hippurate: Prophylaxis/suppression for chronic recurring UTI, after infection eradication by appropriate antimicrobial agent
Methenamine mandelate: Nonspecific bacteriuria due to pyelonephritis, UTI, neurological diseases associatedd with infected residual urine
Pediatric dosage forms and strengths
oral solution
- 500 mg/5mL
tablet, hippurate
- 1g
tablet, mandelate
- 500mg
- 1g
tablet, over the counter
- 162mg methenamine/162.5mg salicylic acid
Methenamine Hippurate
>12 years old: As adult
6-12 years old: 0.5-1 g PO q12hr
<6 years old: Not established
Methenamine Mandelate
>12 years old: As adult
6-12 years old: 500 mg PO q6hr
<6 years old: 18.4 mg/kg PO q6hr
Administration
Mandelate: With meals and at bedtime
Other Information
Over the counter products: Follow directions on labeL
Hiprex, Mandelamine (methenamine) adverse (side) effects
1-10%
Dysuria
Gastric upset
Nausea
Rash
Warnings
Contraindications
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
Cautions
Large doses may cause bladder irritation, urinary frequency, albuminuria, 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
Pregnancy and 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.
Pharmacology of Hiprex, Mandelamine (methenamine)
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 in pts. with severe renal impairment
Mechanism of action
Methenamine hydrolyzes to ammonia and formaldehyde (nonspecific antibacterial) in acidic urine
Mandelic acid or hippuric acid acidify the urine
