Mequitamium iodide (LG 30435) is a quaternary ammonium phenothiazine. Mequitamium iodide was found to bind with high affinity only to histamine H1 receptors and to muscarinic acetylcholine receptors. The (+)-(S)-enantiomer is 10-fold more potent than (-)-(R)-enantiomer as a histamine antagonist, while the two enantiomers show the same antimuscarinic activity in vitro. In animal models, it exerts antiasthmatic and antiallergic properties. It was being clinically investigated as a treatment of asthma and rhinitis.

Clorisamine is an antihistamine drug developed by Schering in the 1970s. The drug was evaluated in phase 1 clinical trial on healthy volunteers. The results show that in a therapeutic dose of 2 mg the drug did not have any effects which might lead to an impairment of driving ability.

Zaltidine (CP-57,361) is a guanidinothiazolylimidazole compound which is a highly specific H2-receptor antagonist. It potently inhibits gastric acid secretion. Zaltidine appears to be an effective treatment of duodenal ulcer in human studies. However, the incidence of hepatic damage (8%) seems higher than with commonly used H2-receptor antagonists.

Napactadine is a bicyclic antidepressant agent. It is a histamine-H1 receptor antagonist. Preliminary results indicated a marked improvement in depressive symptomalology within 7 days of treatment, as measured by the Hamilton depression scale. However, clinical studies were discontinued after chronic administration of napactadine because an elevation in liver enzyme levels was observed in some patients.

Pyroxamine (also known as AHR 224) is benzhydryl ethers of 3-pyrrolidinol patented by A. H. Robins Co., Inc. as antihistamine with bronchodilation activity. In preclinical studies, Pyroxamine shows moderate inhibition of histamine-induced ulceration in guinea pigs

Amoxydramine is tertiary dialkylarylcarbinol derivative patented by American chemical company Allied Chemical Corp as an antitussive, sedative, and antihypertensive agent.

Diethazine is the antimuscarinic agent. It has actions similar to those of ethopropazine but it is more toxic. Diethazine is used for the palliative treatment of the parkinsonian syndrome. It is more useful in the treatment of Parkinson’s disease than in allergies. Blockade of single contractions observed in these experiments after administration of diethazine was independent of the frequency of stimulation of the nerve. This suggests that the drug acts directly on the postsynaptic receptor in the endplate.

Vapitadine (R129160; Hivenyl™) is an antihistamine that Barrier Therapeutics is developing as a treatment for allergic reactions of the skin, such as those associated with hives and for the itch associated with atopic dermatitis. Vapitadine is a new selective, non-sedative H1antihistamine. In several in vitro and in vivo pharmacological models, vapitadine is at least as potent as cetirizine (Zyrtec®) and does not penetrate the blood-brain barrier. An advantage of vapitadine over other antihistamines may be the absence of the sedation, even at high doses. Vapitadine had been in phase II clinical trials for the treatment of patients with atopic dermatitis. However, no development has been reported.

Sulfonterol is a benzenemethanol derivative patented by Smith Kline and French Laboratories as a bronchodilator. Sulfonterol acts as a β-adrenergic partial agonist.