Overview Mechanism reversible inhibition of H1 histamine receptors 1st generation Drugs diphenhydramine (Benadryl) dimenhydrinate (Dramamine) chlorpheniramine hydroxyzine promethazine abused as a recreational drug ("purple drank" or "sizzurp") Clinical uses allergy motion sickness sleep aid Toxicity antimuscarinic anti-α-adrenergic sedation (lipophilic and thus crosses brain barrier) 2nd generation Drugs loratadine (Claritin) fexofenadine (Allegra) cetirizine (Zyrtec) desloratadine Clinical uses allergy Toxicity decreased entry into CNS (lipophobic) makes this generation far less sedating