Pirdonium is an antihistamine agent. It is the hydrophilic Histamine H1 receptor antagonist.

Propinetidine is a piperidinol derivative patented by Farbenfabriken Bayer Akt.-Ges. as antitussive agent.

Methaphenilene, an antihistaminic agent, was studied as a peroxisome proliferator. Information about the current use of this compound is not available.

Trazitiline is an antihistaminic agent.

Tiotidine is a controversial histamine H2 receptor ligand with negligible activity against H1- and H3- receptors. It was found that tiotidine behaves as an inverse agonist in U-937 cells, diminishing basal cAMP levels. Tiotidine showed two binding sites, one with high affinity and low capacity and the other with low affinity and high capacity. Tiotidine is currently in use as a radioligand in histamine H2-receptor binding studies. Compared to cimetidine, tiotidine appears to be approximately eight times more potent on a molar basis than cimetidine as an inhibitor of acid secretion, and the tiotidine effect is more prolonged. It was developed for the treatment of peptic ulcer.

Metiamide is an antagonist of histamine H2-receptors synthesized at Smith Kline & French Laboratories. It potently inhibited gastric acid secretion. Metiamide demonstrated promising clinical effects in patients with duodenal ulcers but questionable safety.

FLEZELASTINE, a phthalazinone derivative, an anti-asthmatic/anti-allergic agent. It exhibits inhibition of histamine release and 5-lipoxygenase, calcium antagonistic properties and antagonism at the histamine H1 receptor. FLEZELASTINE is a racemate consisting of (+)- and (-)-enantiomers. Both enantiomers contribute to the pharmacodynamic efficacy of racemic flezelastine.

Phenamazoline is an antazoline derivative. It is a sympathomimetic agent. It was developed as vasoconstrictor but its carbon analog is a vasodilator.

Donetidine is a potent and long acting histamine H2-receptor antagonist with no H1-receptor antagonist activity. It is a highly basic drug with several amine groups. Donetidine stimulates the release of histamine when given by rapid intravenous infusion to dogs. Symptoms such as vasodilation, watering eye and nose, salivation and collapse, well known indicators of histamine release seen after administration of donetidine.

Elbanizine [HWA 214] is an antihistamine which was undergoing preclinical trials with Hoechst Marion Roussel in Germany for the treatment of allergic asthma. Elbanizine does not have such drawbacks as causing drowsiness or being effective only as a prophylactic drug, and could provide advantages over other non-sedative compounds, such as terfenadine and astemizole, in that it is water soluble and thus can be administered through inhalation or through intravenous application.