Sodium bicarbonate Methenamine

METHENAMINE SODIUM BICARBONATE 1 efficacy of methenamine Methenamine is only effective at a low pH raising the urinary pH 4 its effect Avoid co-administration... 

Pharmaceutical Incompat, (from Remington s Pharmaceutical Sciences) Aspirin forms a damp to pasty mass when triturated with acetanilide, phenacetin, antipyrine, amidopyrine, methenamine, phenol or phenyl salicylate. Powders containing aspirin with an alkali salt such as sodium bicarbonate become gummy on contact with atmospheric moisture. Hydrolysis oecnrs in admixture with salts contg water of crystallization. Solns of the alkaline acetates and citrates, as well as alkalies themselves, dissolve aspirin but the result -ing solns hydrolyze rapidly to form salts of acetic and salicylic acids. Sugar and glycerol have been shown to hinder this decompn. Aspirin very slowly liberates hydriodic acid from potassium or sodium iodide. Subsequent oxidation by air produces free iodine. 

Methenamine and methenamine mandelate are only effective as urinary antisepties if the pH is about 5.5 or lower, when formaldehyde is released. This is normally achieved by giving urinary acidifiers such as ammonium chloride, ascorbic acid, or sodium acid phosphate. In the case of methenamine hippurate, the acidification of the urine is achieved by the presence of hippuric acid. The concurrent use of substances that raise the urinary pH such as acetazolamide, sodium bicarbonate, potassium or sodium citrate is clearly contraindicated. Potassium citrate mixture BPC has been shown to raise the pH by more than 1 at normal therapeutic doses, thereby making the urine sufficiently alkaline to interfere with the activation of methenamine to formaldehyde. Some antacids (containing magnesium, aluminium or calcium as well as sodium bicarbonate mentioned above) can also cause a significant rise in the pH of the urine. ... 

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