• P300;
  • antihistamine;
  • H1-receptor antagonist;
  • astemizole;
  • cetirizine;
  • diphenhydramine;
  • ketotifen;
  • loratadine;
  • terfenadine


Background A comprehensive comparative study of the central nervous system (CNS) properties of newer H1-receptor antagonists is needed.

Objective Our objective was to investigate the central nervous system eifects of u single manufacturer's recommended dose of six H1-receptor antagonists, using appropriate controls.

Methods Fifteen healthy subjects received astemizole 10mg, cetirizine 10mg, ketotifen 2mg, loratadine 10 mg, terfenadine 60mg, diphenhydramine 50mg or placebo. Before and 2-1.5 h after dosing, cognitive function was assessed using the P300-event-related potential, somnolence was assessed using a subjective score, and histamine skin tests were performed.

Results In rank order from least to greatest effect on the P300 latency, the medications were: terfenadine, placebo, cetirizine, ketotifen, loratadine, astemizole and diphenhydramine. Only diphenhydramine increased the P300 latency significantly compared with baseline and placebo. Subjective somnolence was significantly greater than baseline and placebo after cetirizine, ketotifen and diphenhydramine. All the H1-receptor antagonists suppressed the histamine-induced weal significantly compared with baseline.

Conclusions The H1-receptor antagonists tested affected cognitive functioning and somnolence to different extents, although all produced satisfactory peripheral H1-blockade.