Determination of isoniazid half-life from salivary samples

Measurements of isoniazid (INH) half-lives from salivary samples were conducted in 8 healthy volunteers. The study showed a significant positive correlation between salivary and serum INH concentrations (rs = 0.92, n = 50) with the mean saliva/serum concentration ratio of 0.81 (+/- s. e. m. 0.05). The correlation in INH concentration between salivary and serum samples obtained during the elimination phase (rs = 0.92, n = 50) was greater than that obtained during the absorption phase (rs = 0.71, n = 18). The measurements of INH half-lives from salivary samples were very close to those from serum (rs = 0.95, n = 8), and no misclassification into either phenotype was made by using salivary INH half-life for acetylator phenotyping, compared to that by using serum samples. It was concluded, therefore, that INH half-life measurement from saliva could be used as a reliable and convenient method for acetylator phenotyping. However, the calculation of absorption kinetic parameter, of clearance and of the volume of distribution of INH by using salivary samples could not be justified.