Phenytoin concentration in people with epilepsy: a comparative study in serum and saliva Angel Alvarado 1 , Gregoriana García 2 , Alexis Morales 3 , Gustavo Paredes 4 , Miriam Mora 5 , Ana María Muñoz 6 , Ricardo Pariona 7 , María R. Bendezú 8 , Haydee Chávez 8 , Jorge A. García 8 , Doris Laos-Anchante 8 , Berta Loja-Herrera 1 , Mario Bolarte-Arteaga 9 , Mario Pineda 10 1 International Research Network in Pharmacology and Precision Medicine, Human Medicine, San Ignacio de Loyola University, Lima, Peru 2 Department of Neurology, Faculty of Medicine, University Los Andes, Mérida 5101, Venezuela 3 Department of Toxicology and Pharmacology, Faculty of Pharmacy and Bioanalysis, Universidad Los Andes, Mérida, Venezuela 4 Atrium Diagnostic Center, Mérida 5101, Mérida, Venezuela 5 Hospital Tulio Carnevali Salvatierra, Venezuela Institute of Social Security, Mérida 5101, Venezuela 6 Institute of Food Science and Nutrition, ICAN, San Ignacio de Loyola University, Av. La Fontana N° 550, La Molina 15024, Lima, Peru 7 International Research Network in Pharmacology and Precision Medicine, Human Medicine, San Ignacio de Loyola University, La Molina, Peru 8 Faculty of Pharmacy and Biochemistry, San Luis Gonzaga National University of Ica, Ica, Peru 9 Human Medicine, Continental University, Av. Alfredo Mendiola 5210, Los Olivos 15304, Lima, Peru 10Molecular Pharmacology Society of Peru, Av. Alameda del Corregidor 1575, La Molina 15024, Lima, Peru Corresponding author: Angel Alvarado (eaa.alvarado@hotmail.com) Received 31 May 2022  ♦  Accepted 27 July 2022  ♦  Published 24 August 2022 Citation: Alvarado A, García G, Morales A, Paredes G, Mora M, Muñoz AM, Pariona R, Bendezú MR, Chávez H, García JA, Laos-Anchante D, Loja-Herrera B, Bolarte-Arteaga M, Pineda M (2022) Phenytoin concentration in people with epilepsy: a compar- ative study in serum and saliva. Pharmacia 69(3): 809–814. https://doi.org/10.3897/pharmacia.69.e87168 Abstract In clinical practice, therapeutic drug monitoring (TDM) makes it possible to measure the concentration of drugs in serum or saliva, the purpose of which is to reduce adverse efects and optimize pharmacological therapy. Te objective was to determine the concen- trations of Phenytoin in saliva and serum of people with epilepsy. Cross-sectional, descriptive study with dynamic recruitment of 30 people with epilepsy (n = 30; 17 men, 56.7% and 13 women, 43.3%; mean age 33.9 ± 11.83 years). Serum and saliva samples were collected at trough levels from patients, who were under phenytoin treatment for at least three months. Drug levels were assessed by the Cloned Donor Enzyme Immunoassay method. Phenytoin levels were found in saliva between 0.01 to 3.56 mg/L and in serum between 0.09 to 36.60 mg/L. Pearson’s analysis showed an association between the estimated serum and saliva phenytoin concentra- tions (R 2 0.7026; 95% CI 0.685-0.921), with a signifcant statistical correlation (p < 0.05). Te Bland-Altman test broke concordance, the diference between the two saliva/serum methods is within 95% confdence. It is concluded that there is an association and concordance between the concentrations of phenytoin in serum and saliva, therefore, this technique can be useful in the clinical monitoring of phenytoin. Keywords Phenytoin, saliva method, serum, phenytoin monitoring, therapeutic range Copyright Alvarado A et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Pharmacia 69(3): 809–814 DOI 10.3897/pharmacia.69.e87168 Research Article