WEB 2347: pharmacology of a new very potent and long acting hetrazepinoic PAF-antagonist and its action in repeatedly sensitized guinea-pigs.

WEB 2347 is a new hetrazepine which is superior to the previously described paf-antagonists WEB 2086 (apafant) and WEB 2170 (bepafant). This refers to both potency in vitro and in vivo (particularly after oral administration: e.g. the ED50 after oral administration is about 100 times less for WEB 2347 than for WEB 2086 to antagonize paf-induced hypotension in the rat) and duration of action (t1/2 = 41 h in the guinea pig and about 10 h in the rat after p.o. administration). Furthermore the role of paf in active anaphylaxis in vivo, even after repeated microshock, is strengthened.