Saliva testing after single and chronic administration of dihydrocodeine

In the present study, concentrations of dihydrocodeine and its metabolites in saliva and serum were compared after single low-dose and chronic high-do sage administration of the drug. In the first investigation, blood and sali va were collected periodically from six subjects after oral administration of 60 mg dihydrocodeine. In the second study, 20 subjects on oral dihydroco deine maintenance provided single samples of blood and saliva simultaneousl y. Serum protein binding of salivary analytes and their recovery from the a dsorbing material of the collection device as well as pH values of saliva s amples were determined. The fluids were analyzed for dihydrocodeine and the major metabolites by high-performance liquid chromatography. In the single dose study dihydrocodeine was the only analyte found in saliva for up to 1 2-24 h post-dose. The half-life of dihydrocodeine in saliva was about twice that found in blood. The ratios of salival serum concentrations ranged fro m 1.2 to 17.0. After chronic high-dosage use, dihydrocodeine was the main s alivary analyte and N-nordihydrocodeine was present in a few samples. Saliv a/serum concentration ratios of dihydrocodeine were strongly dependent on t he pH value of saliva and, to a lesser extent, on serum-protein binding. Th e salival serum ratios were more similar after chronic administration. The data suggest a passive diffusion process as the underlying mechanism for th e transport of dihydrocodeine into saliva. After both single and chronic us e, the presence of the drug in saliva can be used as evidence of recent sub stance administration.