Salivary phenytoin concentrations in geriatric patients

The concentrations of phenytoin in saliva (Csal) and serum (C) in geriatric patients were compared. Salivary and venous blood samples were collected from 13 patients over 55 years old who were taking oral phenytoin for at least one week. The data of 10 patients were suitable for analysis. Phenytoin concentrations were determined with an immunoassay. Phenytoin Csal/C ratios were calculated. Based on previously reported Csal/C ratios of approximately 0.1 for general patient samples, an expected Csal for each patient was calculated as (C)(0.1). A Student's t test for paired data was used to test for differences between the expected and measured salivary concentrations. The mean Csal/C ratio was 0.098 (S.D. = 0.03, range 0.041-0.152). The correlation between the measured Csal and C was 0.96. There was no significant difference between the expected and measured salivary phenytoin concentrations (p greater than 0.6). This study suggests that age does not affect the ratio of salivary to serum phenytoin concentrations. The wide range of ratios observed, however, indicates that more research is needed before salivary phenytoin concentrations should be used clinically in geriatric patients.