VENOM AND ANTIVENOM

The fauna of Saudi Arabia comprises a large number of venomous species of snakes, fish, scorpions, insects, coelenterates and molluscs. The venoms of these animals show a remarkable diversity of actions on huma n tissues. Neurotoxins (for example, from the Arabian cobra Naja haje arabica) interrupt transmission at peripheral neuromuscular junctions or (for example scorpion neurotoxins) stimulate voltage sensitive syna ptic sodium and potassium channels with release of acetylcholine and c atecholamines. The venoms of Red Sea carnivorous marine snails (genus Conus) contain ''conotoxins'' which have effects on voltage sensitive calcium and sodium channels, acetylcholine receptors, the vasopressin receptor and N-methyl-D-aspartate receptors. Of particular interest ar e sarafotoxins from the venom of the burrowing asp (Atractaspis engadd ensis, Atractaspididae), which cause coronary artery vasoconstriction and atrioventricular block. They are homologous with human endogenous endothelins. Human Victims of bites by this species may die very rapid ly after developing anaphylactic/autonomic symptoms, shock and atriove ntricular conduction abnormalities. Improved ovine Fab fragment antive noms are being developed for treatment of envenoming by Saudi Arabian snakes and scorpions. These Fab antivenoms have the pharmacological ad vantage of more rapid tissue distribution, a larger apparent volume of distribution and less risk of Fc or aggregate-induced complement acti vation than conventional F (ab')(2) antivenoms.