methenamine/sodium acid phosphate

Action and Spectrum

Actions and Spectrum: 

methenamine and sodium acid phosphate are medications used to treat urinary tract infections (UTIs). Let’s discuss their actions and spectrum of activity individually: 

methenamine: 

• Action: methenamine, hexamine, or mandelamine, is a urinary antiseptic. It converts to formaldehyde in an acidic environment, such as the urine. Formaldehyde has bactericidal properties and helps to kill the bacteria causing the infection. 
• Spectrum of Activity: methenamine is primarily effective against Gram-negative bacteria. It is commonly used to prophylaxis or prevent recurrent urinary tract infections caused by susceptible organisms, such as Escherichia coli and Proteus spp. 

sodium acid phosphate: 

• Action: sodium acid phosphate, or monobasic sodium phosphate or MSP, is a urinary acidifier. It lowers the urine’s pH, making the environment more acidic. This acidification helps inhibit certain bacteria’s growth and prevents the formation of urinary calculi (stones). 
• Spectrum of Activity: sodium acid phosphate does not have direct antimicrobial activity. Instead, it creates an unfavorable environment for the growth of certain bacteria by making the urine more acidic. This can help prevent the growth and multiplication of bacteria that thrive in alkaline urine, such as some species of Proteus and Klebsiella. 

Drug Interaction

Adverse Reaction

Frequency defined 

1-10% 

Nausea 

Dysuria 

Rash 

Gastric upset 

Frequency not defined 

Vomiting 

Stomach pain 

Nausea 

Diarrhea 

Black Box Warning

Black Box Warning: 

It is important to note that sodium acid phosphate can interact with other medications, such as those containing aluminum, calcium, or magnesium, and can enhance the risk of kidney damage or other adverse effects.

Additionally, sodium acid phosphate should be avoided in patients with severe renal impairment or those at risk of developing acute phosphate nephropathy, a rare but severe condition characterized by acute kidney injury and high phosphate levels in the blood. 

Furthermore, as sodium acid phosphate is a urinary acidifier, it can increase the risk of certain conditions such as kidney stones or gout. Patients with a prior history of these conditions should use sodium acid phosphate with caution and under the guidance of a healthcare professional. 

Contraindication / Caution

Contraindication/Caution: 

Contraindication 

methenamine and sodium acid phosphate combination products, such as mandelic acid/sodium acid phosphate tablets, may have specific contraindications. Again, please note that the information I provide is based on my knowledge cutoff in September 2021, and it’s essential to consult the most recent prescribing information or a healthcare professional for up-to-date and accurate contraindications. 

The following are potential contraindications associated with methenamine/sodium acid phosphate combination products: 

• Hypersensitivity: Patients with known hypersensitivity or allergy to methenamine, sodium acid phosphate, or any other ingredients in the medication should not use methenamine/sodium acid phosphate combination products. 
• Severe renal impairment: The kidneys primarily excrete methenamine and sodium acid phosphate. Patients with severe renal impairment or ESRD (end-stage renal disease_ may have difficulty eliminating these medications properly. Therefore, caution should be exercised, and dosage adjustments may be necessary. 
• Severe hepatic impairment: methenamine undergoes metabolism in the liver. Patients with severe hepatic impairment may have difficulties metabolizing the drug appropriately. Careful consideration and potential dose adjustment may be required. 
• Acidosis: methenamine requires an acidic environment in the urine to convert into formaldehyde, which exerts its antibacterial effect. Patients with certain types of acidosis, such as renal tubular or severe respiratory acidosis, may have altered urine pH, which can impact the efficacy of methenamine. Caution should be exercised in such cases. 

It is key to consult a healthcare professional or refer to the prescribing information of specific methenamine/sodium acid phosphate combination products for a comprehensive and accurate list of contraindications before using them. 

Caution 

When using methenamine/sodium acid phosphate combination products, there are several cautions to consider. Again, please note that the information I provide is based on my knowledge cutoff in September 2021, and it’s essential to consult the most recent prescribing information or a healthcare professional for up-to-date and accurate cautions. 

The following are potential cautions associated with methenamine/sodium acid phosphate combination products: 

• Renal impairment: methenamine and sodium acid phosphate are excreted primarily by the kidneys. Patients with renal impairment, including mild to moderate renal insufficiency, may require dosage adjustments or close monitoring while using these medications. 
• Hepatic impairment: methenamine undergoes metabolism in the liver. Patients with hepatic impairment may require careful consideration and potential dosage adjustments. 
• Urinary obstruction: methenamine/sodium acid phosphate combination products are not recommended in patients with urinary obstruction, such as urethral strictures or bladder neck obstruction, as they may worsen or interfere with adequate urinary flow. 
• Urinary alkalization: sodium acid phosphate is an acidifying agent to lower urine pH. It is crucial to avoid the concomitant use of urinary alkalinizing agents, such as sodium bicarbonate, which can neutralize the acidifying effects of sodium acid phosphate and reduce its efficacy. 
• Allergic reactions: As with any drug, there is a potential risk of allergic reactions. Patients should be monitored for signs of hypersensitivity or allergic reactions, such as rash, itching, swelling, or difficulty breathing. If any of these symptoms occur contact medical attention should be sought immediately. 
• Drug interactions: methenamine/sodium acid phosphate combination products may interact with other medications. It is crucial to inform healthcare professionals about all the medications, including over-the-counter drugs and herbal supplements, being taken to ensure no potential interactions. 

These are general cautions, and the specific product’s prescribing information should be consulted for a comprehensive and accurate list of cautions and precautions before using methenamine/sodium acid phosphate combination products. 

Pregnancy / Lactation

Pregnancy consideration:  

US FDA pregnancy category: C 

Lactation:   

Excreted into human milk: Yes 

Pregnancy category: 

• Category A: well-controlled and Satisfactory studies do not show risk to the fetus in the first/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: There is no data available for the drug under this category 

Pharmacology

Pharmacology: 

The pharmacology of methenamine/sodium acid phosphate combination products involves the actions of two main components: methenamine and sodium acid phosphate. Let’s explore their pharmacological properties individually: 

methenamine is a urinary antiseptic that exerts its action by converting to formaldehyde in an acidic environment, such as urine. Formaldehyde has bactericidal properties and helps kill the bacteria causing urinary tract infections (UTIs). It disrupts bacterial DNA synthesis and protein structure, leading to bacterial cell death. 

sodium acid phosphate acts as a urinary acidifier. It lowers the pH of the urine, creating an acidic environment. This acidification helps inhibit the growth of certain bacteria and prevents the formation of urinary calculi (stones). It also enhances the effectiveness of methenamine by providing an acidic milieu for the conversion of methenamine to formaldehyde. 

Pharmacodynamics: 

Mechanism of action: methenamine operates by undergoing hydrolysis in acidic urine, producing ammonia and formaldehyde, both of which exhibit bactericidal properties. It’s important to note that methenamine does not convert into formaldehyde when present in serum. 

On the other hand, sodium acid phosphate functions as a urinary acidifier and induces an osmotic effect within the gastrointestinal tract. 

Pharmacokinetics: 

Absorption 

methenamine is not well absorbed from the gastrointestinal tract after oral administration. It remains largely intact until it reaches the acidic environment of the urine. 

sodium acid phosphate is orally administered and absorbed in the gastrointestinal tract. 

Distribution 

methenamine remains mainly localized within the urinary tract after reaching the urine. It does not distribute extensively to other body tissues or fluids. 

After absorption, sodium acid phosphate distributes in body fluids, including the extracellular space. 

Metabolism 

In an acidic environment, such as urine, methenamine undergoes hydrolysis to form formaldehyde, which has bactericidal properties. Formaldehyde is then rapidly metabolized to formic acid, which is further metabolized to carbon dioxide. These metabolic processes occur primarily within the urinary tract. 

sodium acid phosphate is not significantly metabolized in the body. 

Elimination and Excretion 

methenamine and its metabolites, including formic acid and carbon dioxide, are primarily excreted in the urine. They contribute to the localized antibacterial effect in the urinary tract. 

sodium acid phosphate is primarily excreted in the urine, contributing to the acidification of the urinary pH. 

Adminstartion

Administration: 

Oral administration 

methenamine/sodium acid phosphate combination products are typically available as tablets or granules for oral administration. The specific administration instructions may vary depending on the product and its formulation. It is essential to carefully follow the healthcare professional’s instructions or the product labeling. Some general guidelines for the administration of methenamine/sodium acid phosphate: 

• Dosage: The healthcare professional will determine the recommended dosage and duration of treatment typically depend on the specific condition being treated. Adherence to the prescribed dosage and the recommended treatment duration is essential. 
• Oral Administration: methenamine/sodium acid phosphate combination products are usually taken orally with water. Follow the instructions on the product labeling or the healthcare professional’s direction. 
• Timing: methenamine/sodium acid phosphate combination products are often taken after meals to help reduce gastrointestinal side effects. It is essential to follow the recommended timing instructions provided by the healthcare professional or on the product labeling. 
• Swallowing: The tablets should be swallowed whole and not crushed, chewed, or broken unless specifically instructed by the healthcare professional or product labeling. 
• Adequate Fluid Intake: Maintaining a sufficient fluid intake while taking methenamine/sodium acid phosphate is generally recommended to ensure proper urinary flow and help prevent urinary tract infections. 
• Duration of Treatment: methenamine/sodium acid phosphate may vary depending on the condition being treated. It is key to complete the entire course of treatment as prescribed, even if symptoms improve before the treatment is finished. 

Remember, these are general guidelines, and it is key to follow the specific instructions provided by the healthcare professional or the product labeling for the particular methenamine/sodium acid phosphate combination product being used. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: methenamine/sodium acid phosphate 

Why do we use methenamine/sodium acid phosphate? 

methenamine/sodium acid phosphate combination products, such as mandelic acid/sodium acid phosphate tablets, are primarily used to treat and stop urinary tract infections (UTIs). Here are the primary uses of methenamine/sodium acid phosphate: 

• Treatment of UTIs: methenamine/sodium acid phosphate combination products are commonly prescribed to treat lower urinary tract infections caused by susceptible bacteria. methenamine acts as a urinary antiseptic, killing bacteria, while sodium acid phosphate acidifies the urine, creating an unfavorable environment for bacterial growth. 
• Prevention of UTIs: methenamine/sodium acid phosphate combination products are also used for the prevention or prophylaxis of recurrent urinary tract infections. By maintaining an acidic urinary pH, these medications can help inhibit the growth and multiplication of bacteria, reducing the risk of recurrent infections. 

It’s important to note that the specific indications and recommended use may vary depending on the formulation, dosage, and healthcare professional’s judgment. Always follow the instructions and guidance provided by your healthcare professional or the product labeling for the appropriate use of methenamine/sodium acid phosphate combination products.