Effects of sodium fluoride on serum concentrations of selected psychotropic drugs

Caution is imperative when interpreting drug concentrations in blood, plasma, or serum, given the potential variance in the distribution of a compound across these fluids. Preservatives, such as sodium fluoride, prove beneficial in preventing drug degradation in collected blood samples. This study aimed to examine the impact of sodium fluoride on different psychotropic drugs in both serum stabilized with and without this preservative. Paired blood samples (n = 100) were collected at the same time (with and without fluoride) from patients undergoing psychiatric treatment. Samples were examined for different compounds including antidepressants, antipsychotics, antiepileptics, and benzodiazepines using routine liquid chromatography-tandem mass spectrometry methods. Results were statistically evaluated and tested by using a paired t-test (α = 0.05) in order to evaluate possible differences between drug concentrations in samples obtained from blood with or without fluoride. Median concentration ratios (fluoride-stabilized/fluoride-free) of all examined drugs ranged from 0.70 to 1.13 in the patient samples. For most substances exhibiting concentration ratios less than 1, the results indicated that concentrations in the samples with fluoride were, on average, 6%-30% lower than in samples without fluoride. Differences between drug concentrations in the patient samples were mainly attributed to matrix effects and fluoride-induced hemolysis. The latter causing a shift in erythrocytes resulting in serum/plasma dilution, leading to under-/overestimation of a drug. The findings of this study can provide guidance for the interpretation of drug concentrations for therapeutic drug monitoring or assessment of acute drug-induced impairment in cases were fluoridated serum/plasma is used.