Abstract
Purpose. A mechanism-based model is proposed for the analysis of adaptive changes in the pharmacodynamics of benzodiazepines in vivo.
Methods. The pharmacodynamics of midazolam was studied in the kindling model of experimental epilepsy. Concentration-EEC effect data from kindled rats and their controls were fitted to the operational model of agonism. A stepwise procedure was used, allowing changes in the parameters efficacy (τ) and tissue maximum (Em) either separately or in combination. The results were compared to data obtainedin vitro in a brain synaptoneurosomal preparation.
Results. The relationship between midazolam concentration and EEC effect was non-linear. In kindled rats the maximum EEC effect was reduced by 27± 8.3µV from the original value of 94± 4.4µV. Analysis on the basis of the operational model of agonism showed that this decrease could be explained by a difference in the parameter system maximum (Em) rather than efficacy (τ). In the in vitro receptor binding assay no changes in density, affinity or functionality of the benzodiazepine receptor were observed, consistent with the lack of a change in efficacy (τ).
Conclusions. The operational model of agonism provides a mechanistic basis to characterise adaptive changes in the pharmacodynamics of midazolam.
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Cleton, A., Van der Graaf, P.H., Ghijsen, W. et al. Mechanism-Based Modeling of Adaptive Changes in the Pharmacodynamics of Midazolam in the Kindling Model of Epilepsy. Pharm Res 16, 1702–1709 (1999). https://doi.org/10.1023/A:1018949914532
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DOI: https://doi.org/10.1023/A:1018949914532