Second Generation Histamine H-1 Antagonists
- Terfenadine:
- high antagonistic selectivity fo H1-receptors
- non-sedating (poor distribution to CNS)
- high concentrations - proarrhythmic activity (CYP3A inhibitors can increase proarrhymthmic potential (macrolides, HIV protease inhibitors, SSRI antidepressants, etc.)
- Fexofenadine:
- CYP3A metabolite of terfenadine
- high antagonistic selectivity fo H1-receptors
- nonsedating
- no proarrhythmic properties - fewer drug interactions
- Astemizole:
- long-acting (strong receptor association + long-acting 4-OH metabolite)
- some antiadrenergic and anti-serotonergic actions
- nonsedating`
- proarrhythmic (enhanced when metabolism is inhibited - see terfenadine)
- Loratadine
- carbamate function keeps drug peripherally,
- anti-ACh and anti-adrenergic activity
- non-sedating (hydrophilic)
- descarbethoxy metabolite retains high anti-H1 activity
- no proarrhythmic activity
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