Rocastine

Rocastine [AHR-11325, 2-[2-(dimethylamino)ethyl]-2,3-dihydro-4-methylpyrido-[3,2-f]-1,4- oxazepine-5(4H)-thione (E)-2-butenedioate)] is a rapid-acting, potent, nonsedating antihistamine. In guinea pigs challenged with a lethal dose of histamine, rocastine is as effective [based on 1 hr. oral, protective dose (PD50S)] as brompheniramine, chlorpheniramine, pyrilamine, and promethazine and superior to astemizole, diphenhydramine, terfenadine, and oxatomide. Rocastine has a faster onset of action than does terfenadine; rocastine being as effective with a 15 min pretreatment time (PD50 = 0.13 mg/kg) as it is with a 1 hr pretreatment time (PD50 = 0.12 mg/kg), while the 15 min PD50 of terfenadine (PD50 = 44.0 mg/kg) is 22 times greater than the 1 hr PD50 (PD50 = 1.93 mg/kg). Against aerosolized histamine, rocastine was 7.12 x, 2.63 x, and equipotent to pyrilamine in preventing histamine-induced prostration at pretreatment times of 1,3, and 6 hr, respectively. Rocastine protected guinea pigs from collapse induced by aerosolized antigen; rocastine was approximately 36 x more potent (based on 1 hr PD50) than diphenhydramine and as potent as oxatomide and terfenadine. Rocastine did not alter the EEG of cats at doses in vast excess (150x) of its antihistaminic dose nor did it potentiate yohimbine toxicity in mice. Further, rocastine possesses no anticholinergic, antiadrenergic, or antiserotonergic properties in vitro. Rocastine is a selective, nonsedating, H1-antagonist with a rapid onset of action.

The behavioral effects of several histamine H1 antagonists were compared in groups of squirrel monkeys trained to respond under fixed-interval schedules involving response-produced shock or termination of a stimulus associated with shock. Low to intermediate doses of the conventional H1 antagonists chlorpheniramine (up to 3.0 mg/kg), diphenhydramine (up to 1.0 or 3.0 mg/kg), pyrilamine (up to 3.0 mg/kg) and tripelennamine (up to 0.3 or 1.0 mg/kg) produced dose-related increases in response rate under all conditions in which they were studied; higher doses either increased responding less or decreased it. In contrast, a wide range of doses of the novel H1 antagonists AHR 11325 (1.0-30.0 mg/kg), astemizole (up to 10.0 mg/kg) and loratadine (up to 17.0 mg/kg) usually had little effect on responding, although decreases in response rate accompanied by emesis were observed after the highest doses in some monkeys. Other H1 antagonists including phenindamine (0.03-17.0 mg/kg), promethazine (0.03-5.6 mg/kg) and terfenadine (0.1-10.0 mg/kg) had different effects in individual subjects (i.e., dose-related increases in response rate in some monkeys and either little change or dose-related decreases in responding in other monkeys). The dopamine uptake inhibitors cocaine (0.01-1.0 mg/kg) and bupropion (0.1-10.0 mg/kg) had behavioral effects similar to those of chlorpheniramine, diphenhydramine, pyrilamine and tripelennamine, whereas the muscarinic antagonist atropine (0.03-1.0 mg/kg), the serotonin 5-hydroxytryptamine/5-hydroxytryptamine antagonist cyproheptadine (0.03-1.0 mg/kg), the norepinephrine uptake inhibitor desmethylimipramine (0.03-3.0 mg/kg) and the benzodiazepine diazepam (0.3-30.0 mg/kg) produced only dose-related decreases in response rate.(ABSTRACT TRUNCATED AT 250 WORDS)