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This study challenges the assumption that equal reductions in serotonin transporter (SERT) occupancy produce equal biological effects when tapering antidepressants. Using a mathematical model based on mass-action kinetics, researchers found that extracellular serotonin concentrations increase hyperbolically with SERT occupancy, meaning that significant changes in serotonergic signaling occur even within the therapeutic dose range where occupancy appears to plateau. This suggests that the current hyperbolic tapering approach, which assumes proportional relationships between occupancy changes and withdrawal risk, may need refinement.
Why it matters
These findings could inform safer antidepressant discontinuation strategies by revealing that dose reductions within the standard therapeutic range may produce larger biological effects than previously assumed. This has direct implications for millions of patients attempting to taper off serotonin reuptake inhibitors and may help explain why withdrawal symptoms occur even with gradual dose reductions.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Background: Hyperbolic tapering is an increasingly recognized approach for discontinuing serotonin reuptake inhibitor (SRI) antidepressants that involves non-linear dose reductions with equal stepwise reductions in serotonin transporter (SERT) occupancy to mitigate withdrawal symptoms. Its theoretical basis is the hyperbolic relationship between SRI dose and SERT occupancy reported in radioligand imaging studies. Hyperbolic tapering implicitly assumes that changes in SERT occupancy approximate changes in biologic effect and withdrawal risk. Because SERT occupancy plateaus across the therapeutic dose range of SRIs, this framework predicts relatively small biologic effects and withdrawal risk within this range. However, SERT occupancy influences serotonergic activity only indirectly via its effects on extracellular serotonin concentrations, and the relationship between these two variables is poorly characterized. Methods: We developed a two-pathway clearance model derived from mass-action kinetics to evaluate the steady-state relationship between SERT occupancy and extracellular serotonin concentrations under chronic SRI treatment. Results: Our analysis indicates that serotonin concentrations increase hyperbolically as transporter occupancy increases, suggesting that biologically meaningful differences in serotonergic signaling persist across the therapeutic dose range of SRIs despite plateauing occupancy. Conclusions: Our model predicts a hyperbolic relationship between SERT occupancy and extracellular serotonin concentrations, suggesting that changes in occupancy may not map proportionally onto serotonergic effect. These findings provide a potential mechanistic explanation for dose-dependent clinical effects of SRIs despite plateauing transporter occupancy and generate testable hypotheses regarding antidepressant tapering strategies. Empirical validation is warranted.