Introduction:
In child and adolescent psychiatry, measurement of drug concentrations in saliva may
be an interesting non-invasive alternative to therapeutic drug monitoring (TDM) in
blood. However, therapeutic and dose-related reference ranges are defined only for
blood samples. The aim of this study is to assess the correlation between amphetamine
concentration in saliva and serum and to determine the influence of pH on the amphetamine
saliva-to-serum ratio.
Methods:
28 patients (aged 7.4 – 16.9 years, ♂ = 23 ♀ = 5) with attention-deficit/hyperactivity
disorder treated with dexamphetamine or lisdexamphetamine, a prodrug of amphetamine,
were included. Blood and saliva samples were collected simultaneously at the time
of maximum serum concentration of amphetamine. The ratio of saliva/serum concentration
was calculated to analyze the drug distribution in relation to saliva pH. Due to the
exponential relationship between saliva/serum concentration ratio and saliva pH the
ratio was logarithmized for linear testing by Spearman rank correlation (ρ).
Results:
A mean linear relationship between saliva and serum concentration (ρ= 0.628, p < 0.001)
was found. Using logarithmized ratios of saliva/serum concentrations an inverse linear
correlation with saliva pH (ρ=-0.712, p < 0.001) was observed.
Conclusion:
Our findings demonstrate that the pH-value is an important modifier of the salivary
amphetamine concentration. It is known that the salivary flow rate highly influences
the pH of oral fluid, e.g. hyposalivation reduces the physiological buffer capacity
of saliva. On the other hand, hypersalivation stabilizes and increases salivary pH
in oral fluid by higher secretion rate of bicarbonate. Moreover, medication or psychological
factors e.g. stress or anxiety can cause hyposalivation and decrease salivary pH.
Future studies are needed to systematically investigate influencing factors on pH-values
such as saliva flow rate.
