Population pharmacokinetics of clonazepam in saliva and plasma - steps towards non-invasive pharmacokinetic studies in vulnerable populations.

AIM Traditional studies focusing on the relationship between pharmacokinetics (PK) and pharmacodynamics necessitate blood draws which are too invasive for children or other vulnerable populations. A potential solution is to use non-invasive sampling matrices, such as saliva. The aim of this study was to develop a population PK model describing the relationship between plasma- and saliva clonazepam kinetics and assess whether the model can be used to determine trough plasma concentrations based on saliva samples. METHODS Twenty healthy subjects, aged 18-30, were recruited and were administered 0.5mg or 1mg of clonazepam solution. Paired plasma- and saliva samples were obtained until 48h post-dose. A population pharmacokinetic model was developed describing the PK of clonazepam in plasma and the relationship between plasma and saliva concentrations. Bayesian maximum a posteriori (MAP) optimization was applied to estimate the predictive accuracy of the model. RESULTS A two-compartment distribution model best characterized clonazepam plasma kinetics with a mixture component on the absorption rate constants. Oral administration of the clonazepam solution caused contamination of the saliva compartment during the first 4 hours post-dose, after which the concentrations were driven by the plasma concentrations. Simulations demonstrated that the lower and upper limits of agreements between true and predicted plasma concentrations were -28 to 36% with 1 saliva sample. Increasing the number of saliva samples improved these limits to -18 to 17%. CONCLUSION The developed model described the salivary- and plasma kinetics of clonazepam and could predict steady-state trough plasma concentrations based on saliva concentrations with acceptable accuracy.