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Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole.
J Cardiovasc Electrophysiol. 1999 Jun; 10(6):836-43.JC

Abstract

INTRODUCTION

The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels.

METHODS AND RESULTS

HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM).

CONCLUSIONS

Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists.

Authors+Show Affiliations

Section of Cardiology, University of Wisconsin, Madison 53792, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

10376921

Citation

Zhou, Z, et al. "Block of HERG Potassium Channels By the Antihistamine Astemizole and Its Metabolites Desmethylastemizole and Norastemizole." Journal of Cardiovascular Electrophysiology, vol. 10, no. 6, 1999, pp. 836-43.
Zhou Z, Vorperian VR, Gong Q, et al. Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole. J Cardiovasc Electrophysiol. 1999;10(6):836-43.
Zhou, Z., Vorperian, V. R., Gong, Q., Zhang, S., & January, C. T. (1999). Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole. Journal of Cardiovascular Electrophysiology, 10(6), 836-43.
Zhou Z, et al. Block of HERG Potassium Channels By the Antihistamine Astemizole and Its Metabolites Desmethylastemizole and Norastemizole. J Cardiovasc Electrophysiol. 1999;10(6):836-43. PubMed PMID: 10376921.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole. AU - Zhou,Z, AU - Vorperian,V R, AU - Gong,Q, AU - Zhang,S, AU - January,C T, PY - 1999/6/22/pubmed PY - 1999/6/22/medline PY - 1999/6/22/entrez SP - 836 EP - 43 JF - Journal of cardiovascular electrophysiology JO - J Cardiovasc Electrophysiol VL - 10 IS - 6 N2 - INTRODUCTION: The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels. METHODS AND RESULTS: HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM). CONCLUSIONS: Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists. SN - 1045-3873 UR - https://www.unboundmedicine.com/medline/citation/10376921/Block_of_HERG_potassium_channels_by_the_antihistamine_astemizole_and_its_metabolites_desmethylastemizole_and_norastemizole_ L2 - https://onlinelibrary.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=1045-3873&date=1999&volume=10&issue=6&spage=836 DB - PRIME DP - Unbound Medicine ER -