Competitive and stereoselective histamine H1 antagonistic effect of cicletanide in guinea-pig isolated ileum.

The histamine H1 antagonistic effects of the racemic form and the enantiomers of cicletanide, a new antihypertensive furopyridine derivative, were investigated in guinea-pig isolated ileum. Both the racemic and the (-) enantiomer behaved as competitive histamine antagonists (pA2 values of 6.8 and 7.2, respectively). The (+) enantiomer was at least 100 times less potent than the (-) enantiomer. The H1-blocking effect of cicletanide is the most potent and is the only stereoselective property so far reported for the drug.