Emerging safety issues regarding long-term usage of H(1)receptor antagonists

Keynote review: in vitro safety pharmacology profiling: an essential tool for successful drug development

Broad-scale in vitro pharmacology profiling of new chemical entities during early phases of drug discovery has recently become an essential tool to predict clinical adverse effects. Modern, relatively inexpensive assay technologies and rapidly expanding knowledge about G-protein coupled receptors, nuclear receptors, ion channels and enzymes have made it possible to implement a large number of assays addressing possible clinical liabilities. Together with other in vitro assays focusing on toxicology and bioavailability, they provide a powerful tool to aid drug development. In this article, we review the development of this tool for drug discovery, its appropriate use and predictive value.

Adult and paediatric poor metabolisers of desloratadine: an assessment of pharmacokinetics and safety

Antihistamines are widely used to treat allergic rhinitis (AR) and chronic idiopathic urticaria (CIU) in adults and children. Desloratadine is a once-daily oral antihistamine with a favourable sedation profile that is approved for the treatment of AR and CIU. Phenotypic polymorphism in the metabolism of desloratadine has been observed, such that some individuals have a decreased ability to form 3-hydroxydesloratadine, the major metabolite of desloratadine; such individuals are termed 'poor metabolisers of desloratadine'. This review describes the prevalence of poor metabolisers of desloratadine, quantifies the exposure to desloratadine in poor metabolisers and demonstrates that the increased exposure in poor metabolisers is independent of age when administered at age-appropriate doses. Furthermore, this review demonstrates that the increased exposure to desloratadine in poor metabolisers is not associated with any changes in the safety and tolerability profile of desloratadine, including cardiovascular safety.

Mepyramine, a histamine H1 receptor inverse agonist, binds preferentially to a G protein-coupled form of the receptor and sequesters G protein

Accurate characterization of the molecular mechanisms of the action of ligands is an extremely important issue for their appropriate research, pharmacological, and therapeutic uses. In view of this fact, the aim of the present work was to investigate the mechanisms involved in the actions of mepyramine at the guinea pig H(1) receptor stably expressed in Chinese hamster ovary cells. We found that mepyramine is able to decrease the basal constitutive activity of the guinea pig H(1) receptor, to bind with high affinity to a G(q/11) protein-coupled form of the receptor and to promote a G protein-coupled inactive state of the H(1) receptor that interferes with the G(q/11)-mediated signaling of the endogenously expressed ATP receptor, as predicted by the Cubic Ternary Complex Model of receptor occupancy. The effect of mepyramine on ATP-induced signaling was specifically neutralized by Galpha(11) overexpression, indicating that mepyramine is able to reduce G protein availability for other non-related receptors associated with the same signaling pathway. Finally, we found a loss of mepyramine efficacy in decreasing basal levels of intracellular calcium at high Galpha(11) expression levels, which can be theoretically explained in terms of high H(1) receptor constitutive activity. The whole of the present work sheds new light on H(1) receptor pharmacology and the mechanisms H(1) receptor inverse agonists could use to exert their observed negative efficacy.