Determination of Guanfacine in Oral Fluid and Serum of Children and Adolescents With Attention-Deficit/Hyperactivity Disorder: A Short Communication.

BACKGROUND Guanfacine, a selective α2A-adrenoreceptor agonist, is a second-line medication for treating children and adolescents with attention-deficit/hyperkinetic disorder (ADHD). The dosage administered as milligram per body weight to balance the potential benefits and risks of treatment. Therapeutic drug monitoring (TDM) is useful for identifying a patient's therapeutic window to optimize individual drug dosing and reduce the risk of adverse drug reactions. However, in children and adolescents, intravenous sample collection is especially stressful and thus remains a primary challenge, restricting the use of TDM. Therefore, evaluating alternative specimens to facilitate TDM is a worthwhile task. The aim of this study was to assess the feasibility of using oral fluid for TDM of guanfacine in children and adolescents. METHODS Herein, nine patients (median age 8.1 years; 6 boys, 3 girls) undergoing treatment with guanfacine were included. Simultaneously collected oral fluid and serum samples were deproteinized using methanol containing a stable isotope-labeled internal standard prior to the determination of guanfacine by liquid chromatography-tandem mass spectrometry. Pearson's correlation and paired t-test were used for statistical analysis. RESULTS The mean serum guanfacine concentration was three times higher than that detected in oral fluid (7.47 ng/mL vs. 2.36 ng/mL; t (8) = 5.94; P < 0.001). A strong positive linear correlation (r = 0.758, P = 0.018) was identified between oral fluid and serum concentrations. A strong but non-significant negative correlation (r = -0.574, P = 0.106) was detected between the oral fluid pH and oral fluid-to-serum concentration ratio. CONCLUSIONS The strong correlation between oral fluid and serum concentration and the probable small effect of oral fluid pH on oral fluid-to-serum concentration ratio supports guanfacine as a suitable candidate for TDM in oral fluid.