ABSTRACT
BACKGROUND: Histamine is responsible for the wheal and flare reaction in various allergic conditions. Classical antihistamines are the drugs which block the H 1 receptors and are widely used in various allergic conditions, whereas H 2 blockers are mainly used for acid peptic disease. Although H 1 receptor-mediated actions of histamine are primarily responsible for vasodilatation, vasopermeability, and itching, it has been observed that combined blocking of both H1 and H2 receptors may provide better relief. AIM: To compare the efficacy of levocetirizine (H1 blocker) versus levocetirizine and ranitidine (H2 blocker) in suppressing histamine-induced wheal. METHODS: Fifteen volunteers were given a single dose of levocetirizine 5 mg on day 1 and a single dose of levocetirizine 5 mg with ranitidine 150 mg twice a day on day 7. A pretest was performed by intradermal histamine prick test. After administration of the drugs, the prick test was repeated at 1 hour, 2, 3, 6, and 24 hours, and the size of the wheal measured and statistically analyzed. RESULTS: At 1 hour, there was no statistically significant difference in the wheal size between levocetirizine alone and the combination of levocetirizine and ranitidine. Levocetirizine with ranitidine resulted in statistically significant reduction of wheal size at 2, 3, 6, and 24 hours when compared with levocetirizine alone. CONCLUSION: H2 blocker potentiates the effects of an H1 blocker in suppressing histamine-induced wheal.
ABSTRACT
BACKGROUND: Histamine is the major mediator of allergic reactions. Newer H1 antihistaminics like levocetirizine, fexofenadine, and desloratadine are used in the treatment of seasonal and perennial allergic rhinitis and urticaria. The ability to block the cutaneous response to intradermal histamine is used to evaluate the potential of antihistamines. AIMS: To compare the potency, onset, and duration of action of the commonly used antihistamines-levocetirizine, fexofenadine, and desloratadine. METHODS: Thirty volunteers were given three single doses of levocetirizine, fexofenadine and desloratadine at weekly intervals. A pretest was performed by using the intradermal histamine prick test. After administration of the drugs, the intradermal test was repeated at (1/2), 1, 2, 3, 6 and 24 h, and the sizes of the wheal were measured. The mean values were taken and were compared by using Levene's t-test. RESULTS: At 30 min, fexofenadine showed a statistically significant suppression of wheal size compared to levocetirizine and desloratadine. Two and three hours after administration, levocetirizine and fexofenadine showed statistically significant inhibition of wheal size while only levocetirizine had this effect after six hours when compared to desloratadine. Desloratadine showed greater inhibition of wheal size at the end of 24 h when compared to levocetirizine and fexofenadine but this was not statistically significant. CONCLUSIONS: Fexofenadine had the earliest onset of action while levocetirizine showed maximum inhibition of wheal response after three and six hours.