Cetirizine and loratadine: a comparison using the ED50 in skin reactions.
To quantify objectively the comparative potencies of the antihistamines, loratadine and cetirizine, we determined the dose that inhibits histamine-induced skin reactions by 50% of the maximum response (ED50) for each drug. Cetirizine at 2.5, 5 or 10 mg, loratadine at 10, 20 or 40 mg or placebo were given to 14 healthy female subjects in a randomized double-blind crossover design. Inhibition of the wheal and flare response to the histamine prick test (10, 100 and 500 mg/ml) was evaluated. Depending on the histamine concentrations, the ED50s for wheals were in the ranges 4.3 - 4.7, 2.1 - 2.2 and 1.7 - 1.9 mg cetirizine, 2, 4 and 6 h after dosing, respectively. For loratadine, the ED50 for wheals were in the ranges 35.6 - > 40, 9.1 - 24.1 and 9.1 - 13.9 mg, 2, 4 and 6 h after dosing, respectively. Calculation of the ED50 demonstrated that, on average, cetirizine is seven to nine times more potent than loratadine at inhibiting wheal and flare reactions.
Ramboer
I
I
UCB SA Pharma Sector, Braine l'Alleud, Belgium.
Bumtbacea
R
R
Lazarescu
D
D
Radu
J R
JR
D000328:Adult; D017332:Cetirizine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006632:Histamine / Q000276:immunology; D006634:Histamine H1 Antagonists / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D017336:Loratadine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D012867:Skin / Q000276:immunology / Q000473:pathology; D012882:Skin Tests
D006634:Histamine H1 Antagonists; D017336:Loratadine; D006632:Histamine; D017332:Cetirizine