Since the classic paper of Hanzlik and Collins,1 the use of methenamine has been greatly restricted, and it finds its chief application as a urinary antiseptic in acid urines. In this work acid sodium phosphate is suggested as an acidifying agent, and this suggestion is now found in most textbooks. Since that time ammonium chloride has been recommended for the same purpose, and Helmholz2 reported favorably on the combined use of methenamine and ammonium chloride in pyelitis in children.
Trendelenburg3 reported the dissociation curve of methenamine at increasing degrees of acidity. At a pH of 5.2 and at a temperature of 38 C., about 8 per cent of the drug is hydrolyzed in six hours. In two hours considerably less than this, approximately 3.4 per cent will be converted into formaldehyde. At a PH of 6.3, about 1 per cent is hydrolyzed in two hours. In six hours he found
WISE EC, HEYL FW. A CHEMICAL STUDY OF URINE AS EFFECTED BY COMBINATIONS OF AMMONIUM CHLORIDE AND METHENAMINE. Arch Intern Med (Chic). 1929;44(2):252–262. doi:https://doi.org/10.1001/archinte.1929.00140020100008
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