methenamine/hyoscyamine

Action and Spectrum

Actions and Spectrum: 

Actions 

methenamine is a urinary tract antiseptic. When ingested, it is converted into formaldehyde in acidic urine. Formaldehyde has bactericidal properties and helps to prevent or treat urinary tract infections by killing or inhibiting bacterial growth in the urinary system. 

Spectrum 

methenamine is particularly effective against certain types of bacteria, such as Escherichia coli, which commonly cause UTIs. methenamine is often used as a prophylactic agent in individuals prone to recurrent UTIs. 

hyoscyamine is primarily used for the symptomatic relief of smooth muscle spasms in the gastrointestinal (GI) tract. It can be helpful in conditions such as irritable bowel syndrome (IBS), colic, and certain forms of abdominal pain. 

Drug Interaction

Adverse Reaction

Frequency defined 

>10% 

Dry skin 

1-10% 

Gastric upset 

Dysuria 

Rash 

Nausea 

Constipation 

Blurred vision 

Photosensitivity 

Dysphagia 

<1% 

Tachycardia 

Orthostatic hypotension 

Headache 

Black Box Warning

Black Box Warning: 

None 

Contraindication / Caution

Contraindication/Caution: 

Contraindications 

• Hypersensitivity 
• Glaucoma 
• Renal impairment 

Cautions 

• Urinary obstruction 
• Gastrointestinal conditions 
• Myasthenia gravis 
• Pregnancy 
• Lactation 

Pregnancy / Lactation

Pregnancy consideration:  

Pregnancy Category: C 

Breastfeeding warnings:  

Caution should be exercised while administering the drug to breastfeeding women. 

Pregnancy category: 

Category A: well-controlled and satisfactory studies show no risk to the fetus in the first or later trimester. 

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women. 

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.    

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.    

Category N: No data is available for the drug under this category. 

Pharmacology

Pharmacology:  

methenamine and hyoscyamine have distinct pharmacological actions and are used for different purposes. methenamine is primarily used as a urinary tract antiseptic, while hyoscyamine is an antimuscarinic agent for its antispasmodic effects. 

Pharmacodynamics: 

methenamine is converted to formaldehyde in acidic urine. Formaldehyde exerts its antimicrobial effects by alkylating and damaging the DNA and proteins of microorganisms, leading to their death or inhibition of growth. 

The antimicrobial action of formaldehyde helps prevent or treat urinary tract infections (UTIs) by targeting and killing bacteria in the urinary system. 

The antispasmodic effects of hyoscyamine are beneficial in the gastrointestinal (GI) tract, where it helps relieve smooth muscle spasms associated with conditions such as irritable bowel syndrome (IBS) or colic. 

Pharmacokinetics: 

Absorption 

The drug is 10-30% hydrolyzed in the gastric cavity if not coated with an enteric tablet 

Distribution 

The peak urine concentration is achieved in 2-8 hours 

Metabolism 

The drug gets metabolized 10-25% in the liver. 

Elimination and Excretion 

The half-life of the drug is 3-6 hours 

The drug is excreted 90% in the urine 

Adminstartion

Administration: 

methenamine/hyoscyamine is typically administered orally as tablets or capsules. It is usually taken with water after meals to ensure proper absorption and minimize potential gastrointestinal side effects. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: methenamine/hyoscyamine 

Why do we use methenamine/hyoscyamine? 

methenamine is primarily used as a urinary tract antiseptic. It prevents or treats urinary tract infections (UTIs) caused by susceptible bacteria. hyoscyamine helps relieve smooth muscle spasms in various body parts, especially the gastrointestinal (GI) tract. It manages conditions such as irritable bowel syndrome (IBS), colic, and specific abdominal pain associated with smooth muscle spasms.