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methenamine/hyoscyamine (Prosed DS, Darpaz, Urelle, Uretron D/S, Uribel, Urimar-T, Urogesic Blue, Uticap, Utrona-C)

 

Classes: Antibiotics, Other

Dosing and uses of Prosed DS, Darpaz (methenamine/hyoscyamine)

 

Adult dosage forms and strengths

methenamine/hyoscyamine

tablet

  • 81mg/0.12mg

tablet, capsule

  • 120mg/0.12mg

 

Urinary Tract Infection Prophylaxis

1 tablet/capsule PO q6hr with liberal fluid intake

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

Hyoscyamine: Adjunctive treatment for lower urinary tract hypermotility and spasm

 

Pediatric dosage forms and strengths

tablet

  • 81 mg/0.12mg

tablet, capsule

  • 120 mg/0.12mg

 

Urinary Tract Infection Prophylaxis

<16 years: Safety/efficacy not established

≥16 years: 1 tablet/capsule PO q6hr with liberal fluid intake

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

Hyoscyamine: Adjunctive treatment for lower urinary tract hypermotility and spasm

 

Geriatric dosage forms and strengths

Avoid hyoscyamine except in short-term situations to decrease secretions; high incidence of anticholinergic effects (Beers criteria)

 

Prosed DS, Darpaz (methenamine/hyoscyamine) adverse (side) effects

>10%

Hyoscyamine

  • Dry skin

 

1-10%

Methenamine

  • Dysuria
  • Discoloration of urine (blue)
  • Gastric upset
  • Nausea
  • Rash

Hyoscyamine

  • Blurred vision
  • Constipation
  • Dysphagia
  • Photosensitivity

 

<1%

Hyoscyamine

  • Headache
  • Orthostatic hypotension
  • Tachycardia

 

Warnings

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

Hyoscyamine

  • Hypersensitivity to hyoscyamine or related compounds
  • Closed-angle glaucoma, myasthenia gravis, hemorrhage w/ cardiovascular instability, paralytic ileus, intestinal atony of elderly/debilitated pt, obstructive uropathy, toxic megacolon, GI obstruction, tachycardia secondary to cardiac insufficiency or thyrotoxicosis
  • Breastfeeding

 

Cautions

Methenamine

  • Large doses may cause bladder irritation, urinary frequency, albuminuria, and hematuria
  • Maintain acidic pH of urine, esp. 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

Hyoscyamine

  • Renal/hepatic impairment, BPH, CHF, CAD, HTN, COPD, hiatal hernia, reflux esophagitis, mitral stenosis, brain damage or spastic paralysis in children, salivary secretion disorder, Down syndrome, autonomic neuropathy, hyperthyroidism, tachyarrythmia, toxin-mediated diarrhea
  • Elderly

 

Pregnancy and lactation

Pregnancy category: C

Lactation: hyoscyamine and methenamine excreted in human milk; caution in breastfeeding women

 

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 Prosed DS, Darpaz (methenamine/hyoscyamine)

Mechanism of action

Methenamine: Hydrolyzed in acidic urine to ammonia and formaldehyde, which are bactericidal agents; does not convert to formaldehyde in serum

Hyoscyamine: Elicits anticholinergic activity; decreases urinary spasms with cystitis

Additional ingredients in some products: Methylene blue (weak antiseptic properties); sodium phosphate monobasic (acidifier); phenyl salicylate (mild analgesic)

 

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

Liver (10-25%)

 

Elimination

Half-Life: 3-6 hr

Excretion: urine (90%)