Dosing & Uses
Dosage Forms & Strengths
methenamine/hyoscyamine
tablet
- 81mg/0.12mg
tablet, capsule
- 120mg/0.12mg
Urinary Tract Irritative Voiding Symptoms
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
Dosage Forms & 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
Avoid hyoscyamine except in short-term situations to decrease secretions; high incidence of anticholinergic effects (Beers criteria)
Interactions
Interaction Checker
No Results

Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor

Contraindicated (0)
Serious - Use Alternative (13)
- 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.
- glucagon
glucagon increases toxicity of hyoscyamine by Other (see comment). Avoid or Use Alternate Drug. Comment: Coadministration of anticholinergic drugs and glucagon increase the risk of gastrointestinal adverse reactions due to additive effects on inhibition of gastrointestinal motility. .
- glucagon intranasal
glucagon intranasal increases toxicity of hyoscyamine by Other (see comment). Avoid or Use Alternate Drug. Comment: Coadministration of anticholinergic drugs and glucagon increase the risk of gastrointestinal adverse reactions due to additive effects on inhibition of gastrointestinal motility. .
- glycopyrronium tosylate topical
glycopyrronium tosylate topical, hyoscyamine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Coadministration of glycopyrronium tosylate topical with other anticholinergic medications may result in additive anticholinergic adverse effects.
- microbiota oral
methenamine decreases effects of microbiota oral by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Microbiota oral contains bacterial spores. Antibacterial agents may decrease efficacy if coadministered. Complete antibiotic regimens 2-4 days before initiating microbiota oral. .
- pramlintide
pramlintide, hyoscyamine. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Synergistic inhibition of GI motility.
- revefenacin
revefenacin and hyoscyamine both decrease cholinergic effects/transmission. Avoid or Use Alternate Drug. Coadministration may cause additive anticholinergic effects.
- secretin
hyoscyamine decreases effects of secretin by pharmacodynamic antagonism. Avoid or Use Alternate Drug. Concomitant use of anticholinergic drugs may cause a hyporesponse to stimulation testing with secretin. Discontinue anticholinergic drugs at least 5 half-lives before administering secretin.
- 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.
- umeclidinium bromide/vilanterol inhaled
hyoscyamine, umeclidinium bromide/vilanterol inhaled. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Concomitant use with other anticholinergic-containing drugs may lead to additive anticholinergic adverse effects.
Monitor Closely (86)
- abobotulinumtoxinA
abobotulinumtoxinA increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Use of anticholinergic drugs after administration of botulinum toxin-containing products may potentiate systemic anticholinergic effects. .
- aclidinium
hyoscyamine and aclidinium both decrease cholinergic effects/transmission. Use Caution/Monitor.
- amantadine
hyoscyamine, amantadine. Mechanism: pharmacodynamic synergism. Use Caution/Monitor. Potential for increased anticholinergic adverse effects.
- amitriptyline
hyoscyamine and amitriptyline both decrease cholinergic effects/transmission. Use Caution/Monitor.
- amoxapine
hyoscyamine and amoxapine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- anticholinergic/sedative combos
anticholinergic/sedative combos and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- aripiprazole
hyoscyamine decreases levels of aripiprazole by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of aripiprazole by pharmacodynamic antagonism. Use Caution/Monitor.
aripiprazole increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - atracurium
atracurium and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- atropine
atropine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- atropine IV/IM
atropine IV/IM and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- belladonna alkaloids
belladonna alkaloids and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- belladonna and opium
hyoscyamine and belladonna and opium both decrease cholinergic effects/transmission. Use Caution/Monitor.
- benperidol
hyoscyamine decreases levels of benperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of benperidol by pharmacodynamic antagonism. Use Caution/Monitor.
benperidol increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - benztropine
benztropine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor. Additive anticholinergic adverse effects may be seen with concurrent use.
- bethanechol
bethanechol increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- buprenorphine, long-acting injection
buprenorphine, long-acting injection increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Coadministration of buprenorphine with anticholinergic drugs may increase risk of urinary retention and/or severe constipation, which may lead to paralytic ileus.
- carbachol
carbachol increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- cevimeline
cevimeline increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- chlorpromazine
hyoscyamine decreases levels of chlorpromazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of chlorpromazine by pharmacodynamic antagonism. Use Caution/Monitor.
chlorpromazine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - cisatracurium
cisatracurium and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- clomipramine
hyoscyamine and clomipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- clozapine
hyoscyamine decreases levels of clozapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of clozapine by pharmacodynamic antagonism. Use Caution/Monitor.
clozapine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - cyclizine
cyclizine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- cyclobenzaprine
cyclobenzaprine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- darifenacin
darifenacin and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- desipramine
hyoscyamine and desipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- dicyclomine
dicyclomine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- diphenhydramine
diphenhydramine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- donepezil
donepezil increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- donepezil transdermal
donepezil transdermal, hyoscyamine. Either decreases effects of the other by pharmacodynamic antagonism. Use Caution/Monitor.
- dosulepin
hyoscyamine and dosulepin both decrease cholinergic effects/transmission. Use Caution/Monitor.
- doxepin
hyoscyamine and doxepin both decrease cholinergic effects/transmission. Use Caution/Monitor.
- droperidol
hyoscyamine decreases levels of droperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of droperidol by pharmacodynamic antagonism. Use Caution/Monitor.
droperidol increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - echothiophate iodide
echothiophate iodide increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- fesoterodine
fesoterodine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- flavoxate
flavoxate and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- fluphenazine
hyoscyamine decreases levels of fluphenazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of fluphenazine by pharmacodynamic antagonism. Use Caution/Monitor.
fluphenazine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - galantamine
galantamine increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- glycopyrrolate
glycopyrrolate and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- glycopyrrolate inhaled
glycopyrrolate inhaled and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- haloperidol
hyoscyamine decreases levels of haloperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of haloperidol by pharmacodynamic antagonism. Use Caution/Monitor.
haloperidol increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - henbane
henbane and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- homatropine
homatropine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- huperzine A
huperzine A increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- hydroxyzine
hydroxyzine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- iloperidone
hyoscyamine decreases levels of iloperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of iloperidone by pharmacodynamic antagonism. Use Caution/Monitor.
iloperidone increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - imipramine
hyoscyamine and imipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- ipratropium
hyoscyamine and ipratropium both decrease cholinergic effects/transmission. Use Caution/Monitor. Due to the poor systemic absorption of ipratropium, interaction unlikely at regularly recommended dosages.
- levodopa
hyoscyamine, levodopa. Other (see comment). Use Caution/Monitor. Comment: Anticholinergic agents may enhance the therapeutic effects of levodopa; however, anticholinergic agents can exacerbate tardive dyskinesia. In high dosage, anticholinergics may decrease the effects of levodopa by delaying its GI absorption. .
- lofepramine
hyoscyamine and lofepramine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- loxapine
hyoscyamine decreases levels of loxapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of loxapine by pharmacodynamic antagonism. Use Caution/Monitor.
loxapine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - loxapine inhaled
loxapine inhaled increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.
hyoscyamine decreases levels of loxapine inhaled by pharmacodynamic antagonism. Use Caution/Monitor. - maprotiline
hyoscyamine and maprotiline both decrease cholinergic effects/transmission. Use Caution/Monitor.
- meclizine
hyoscyamine and meclizine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- methscopolamine
hyoscyamine and methscopolamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- metoclopramide intranasal
hyoscyamine will decrease the level or effect of metoclopramide intranasal by Other (see comment). Use Caution/Monitor. Coadministration of metoclopramide intranasal with drugs that impair GI motility may decrease systemic absorption of metoclopramide. Monitor for reduced therapeutic effect.
- neostigmine
neostigmine increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- nortriptyline
hyoscyamine and nortriptyline both decrease cholinergic effects/transmission. Use Caution/Monitor.
- olanzapine
hyoscyamine decreases levels of olanzapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of olanzapine by pharmacodynamic antagonism. Use Caution/Monitor.
olanzapine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - oliceridine
hyoscyamine increases toxicity of oliceridine by Other (see comment). Use Caution/Monitor. Comment: Anticholinergic drugs may increase risk of urinary retention and/or severe constipation, which may lead to paralytic ileus. Monitor for signs of urinary retention or reduced gastric motility if oliceridine is coadministered with anticholinergics.
- onabotulinumtoxinA
onabotulinumtoxinA and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- orphenadrine
hyoscyamine and orphenadrine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- oxybutynin
hyoscyamine and oxybutynin both decrease cholinergic effects/transmission. Use Caution/Monitor.
- oxybutynin topical
hyoscyamine and oxybutynin topical both decrease cholinergic effects/transmission. Use Caution/Monitor.
- oxybutynin transdermal
hyoscyamine and oxybutynin transdermal both decrease cholinergic effects/transmission. Use Caution/Monitor.
- paliperidone
hyoscyamine decreases levels of paliperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of paliperidone by pharmacodynamic antagonism. Use Caution/Monitor.
paliperidone increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - pancuronium
hyoscyamine and pancuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.
- perphenazine
hyoscyamine decreases levels of perphenazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of perphenazine by pharmacodynamic antagonism. Use Caution/Monitor.
perphenazine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - physostigmine
physostigmine increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- pilocarpine
pilocarpine increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- pimozide
hyoscyamine decreases levels of pimozide by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of pimozide by pharmacodynamic antagonism. Use Caution/Monitor.
pimozide increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - prabotulinumtoxinA
hyoscyamine, prabotulinumtoxinA. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Use of anticholinergic drugs after administration of botulinum toxin-containing products may potentiate systemic anticholinergic effects.
- pralidoxime
hyoscyamine and pralidoxime both decrease cholinergic effects/transmission. Use Caution/Monitor.
- prochlorperazine
hyoscyamine decreases levels of prochlorperazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of prochlorperazine by pharmacodynamic antagonism. Use Caution/Monitor.
prochlorperazine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - promethazine
hyoscyamine decreases levels of promethazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of promethazine by pharmacodynamic antagonism. Use Caution/Monitor.
promethazine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - propantheline
hyoscyamine and propantheline both decrease cholinergic effects/transmission. Use Caution/Monitor.
- protriptyline
hyoscyamine and protriptyline both decrease cholinergic effects/transmission. Use Caution/Monitor.
- 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.
- pyridostigmine
pyridostigmine increases and hyoscyamine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.
- quetiapine
hyoscyamine decreases levels of quetiapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of quetiapine by pharmacodynamic antagonism. Use Caution/Monitor.
quetiapine increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - rapacuronium
hyoscyamine and rapacuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.
- risperidone
hyoscyamine decreases levels of risperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.
hyoscyamine decreases levels of risperidone by pharmacodynamic antagonism. Use Caution/Monitor.
risperidone increases effects of hyoscyamine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia. - rocuronium
hyoscyamine and rocuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.
- scopolamine
hyoscyamine and scopolamine both decrease cholinergic effects/transmission. Use Caution/Monitor.
- 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.
- solifenacin
hyoscyamine and solifenacin both decrease cholinergic effects/transmission. Use Caution/Monitor.
Minor (3)
- dimenhydrinate
dimenhydrinate increases toxicity of hyoscyamine by pharmacodynamic synergism. Minor/Significance Unknown. Additive anticholinergic effects.
- donepezil
donepezil decreases effects of hyoscyamine by pharmacodynamic antagonism. Minor/Significance Unknown.
- galantamine
galantamine decreases effects of hyoscyamine by pharmacodynamic antagonism. Minor/Significance Unknown.
Adverse 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 & 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
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%)