Pharmacokinetics of Nitrazepam in Saliva and Serum after a Single Oral Dose

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Abstract
The pharmacokinetics of nitrazepam in saliva and serum was studied in 12 healthy volunteers after a single administration of a 5 mg nitrazepam tablet. The binding of nitrazepam to plasma proteins was determined 4 hours after the administration by ultracentrifugation. The analysis of nitrazepam concentrations was performed by 63Ni-EC-GLC. The pharmacokinetic parameters were evaluated manually or by AUTOAN-program in serum, and manually in saliva. The concentrations of nitrazepam in serum and saliva correlated significantly (r=0.472, P<0.001, n=97). The ratio saliva: serum was, however, time dependent. The protein free fraction in serum was significantly higher (P<0.01) than the salivary concentration at the same time (4 hours after administration). The peak concentrations in serum and saliva were 40.7 and 1.9 ng/ml (P<0.001) and the times to reach the peak maximum 2.4 and 2.5 hours, respectively (difference not significant). The mean half-life of nitrazepam in serum was 30.5 hrs and in saliva 39.9 hrs, the difference being significant at P<0.05. The distribution phase parameters, poorly described before, were calculated. The clinical value of nitrazepam analysis in saliva seems to be negligible.