Comparison of Unbound and Total Serum Theophylline Concentrations with Those of Stimulated and Unstimulated Saliva in Asthmatic Children

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Abstract
Unstimulated saliva, citric acid stimulated saliva, and serum were collected from 31 asthmatic children taking theophylline. Salivary theophylline concentrations, and total and unbound serum theophylline concentrations were measured. The correlation coefficients between both types of saliva, and total and unbound serum theophylline were all statistically significant (p < 0.001). The highest correlation coefficients were obtained with stimulated saliva and total serum concentrations (r = 0.98), and stimulated saliva and unbound serum (r = 0.96). The coefficients when unstimulated saliva was compared to either total or unbound serum concentrations were 0.90 and 0.89, respectively. Serum binding of theophylline averaged 58.1%. Unstimulated saliva had a higher mean theophylline concentration than stimulated saliva. The results suggest that salivary monitoring using stimulated saliva may be used to predict serum concentrations with a high degree of confidence when the saliva levels are substantially lower than, higher than, or in the middle of the therapeutic range, but there is a considerable degree of uncertainty when the salivary values are near the lower or upper end of the therapeutic range.