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Compounds with combined histamine H1- and H2-receptor antagonist activity were synthesized by connecting H1- and H2-receptor substructures via cyanoguanidine, urea, or nitroethenediamine moieties. Loss of the strongly basic side-chain nitrogen results in a decrease of H1-receptor activity compared to single reference compounds. At the guinea-pig right atrium (H2-receptor model) compounds with mepyramine or cyclizine structure are also less active than the single references tiotidine, ranitidine, or lamtidine. Nevertheless substances with a pheniramine like partial structure proved to be potent histamine H2-receptor antagonists at the atrium model (about 27 times more active than cimetidine).

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