Antihistaminic efficacy of Ranitidine with & without Dimethendine maleate on histamine-induced cutaneous reactions.

The effect of Ranitidine, the H2-receptor antagonist, was investigated on cutaneous response to intradermal injection of histamine in healthy volunteers in a controlled, randomized, cross over study. The response was compared with that of the H1-receptor blocker; Dimethendine maleate used alone and in combination with the two antagonists. Reduction in the wheal area was significant in subjects pretreated with Ranitidine alone (P less than 0.05), and Dimethendine maleate alone (P less than 0.05); the combination of the two antagonists, did not produce additional reduction. Reduction in erythema area was not significant with Dimethendine maleate alone, but significant with Ranitidine alone (P less than 0.01). With the combination of the two antagonists the reduction was not more significant than with Ranitidine alone. The flare response scoring on visual analogue scale was not reduced significantly by Dimethendine maleate alone but reduced significantly by Ranitidine alone (P less than 0.10), and by combination of Ranitidine and Dimethendine maleate (P less than 0.05). Thus, Ranitidine appears to be more effective than Dimethendine maleate in reducing the erythema area and intensity of flare response and equieffective in reducing wheal response to histamine injection.

Relative bioactivity of histamine and slow reacting substance of anaphylaxis released during anaphylactic reaction from different tissues of guinea pigs and rats.

Relative amount of histamine and SRS-A released during Schultz Dale reaction were indirectly estimated. Percent block produced by specific antagonists, mepyramine and FPL 55712, on antigen induced response in various tissues was compared with controls. The relative bioactivity of histamine and SRS-A released was 93% and 7%, respectively, in rat lungs: 37% and 63% in guinea pig lungs; 82% and 18% in guinea pig intestine, 59% and 41% in rat intestine and 100% and 0% in skin of guinea pig and rats. Expectedly, individual experiments showed gross variations because anaphylaxis is rarely dose related.