<prompt> Methanamine salts are used as urinbary antiseptics. The reason theylack systemic antibacterial action is that they are:Not absorbed into systemic circulation after oral useRapidly metabolized by liver drug metabolizing enzymesConveed to formaldehyde at low urinary pHSubstrates for active tubular secretion  <response>: Ref: KDT 6e p735 Methanamine mandelate is used as an urinary antiseptic. It acts by conversion to formaldehyde at acidic urinary pH. Mandelic acid formed from this salt also serves the function of urinary acidifying agent. These are not effective against proteus because proteus results in the formation of ammonia which alkalinizes the urine. 