Urinary Elimination of Nitrazepam and its Main Metabolites

Nitrazepam and its main metabolites, 7-aminonitrazepam and 7-acetamidonitrazepam, free and conjugated, were determined in the human urine after a single oral dose of 5 mg. The determinations were performed by GLC method using 63Ni-EC-detector for unchanged nitrazepam and nitrogen selective detector for the metabolites. Unchanged nitrazepam was poorly eliminated through the kidneys (about 1% of the dose). The interindividual variation of total excreted urinary metabolites was large ranging between 848-4933 microgram (17-99% of the dose during 7 days). Of this amount conjugated metabolites made up 57%. The urinary half-lives of free and conjugated-7-aminonitrazepam were (mean and ranges) 44 (23-65) and 46 (25-69) hrs, and of 7-acetamidonitrazepam 12 (5-31) and 18 (5-46) hrs, respectively. The half-lives of the excreted amounts of the metabolites did not correlate with any pharmacokinetic parameter of unchanged nitrazepam in serum.