The pharmacokinetics of Iranian scorpion Odonthubuthus doriae venom and the available antivenom

In Iran intramuscular (IM) administration of antivenoms is used for the treatment of human scorpion envenoming of six medically dangerous scorpion species, including Odonthubuthus doriae (O. doriae). The purpose of the current study is to investigate the efficiency of the intramuscular route and the delay of injection on the neutralizing effect of the available polyvalent antivenom. We compared the pharmacokinetics parameters of O. doriae venom and its antivenom. 5µg (131)I-labeled venom and 0.2µl of antivenom were administered via subcutaneous (SC) or IM into rats. Blood samples were taken at various predetermined time intervals during a 24hr period for the venom and a 360min period for the antivenom. The radio-iodination was carried out using the chloramin-T method. The results showed that pharmacokinetic parameters of the venom were T(1/2) = 496.53min; V(d) = 1522ml/kg; Cl = 2.12 ml/kg/min; mean resident residual time (MRT) = 555.77min, and for the antivenom T(1/2) = 902.13min, V(d) = 666.66 ml/kg , Cl = 0.512 ml/kg/min and MRT = 1292min. The total body clearance of the venom is relatively low in agreement with a high mean residence time. Higher AUC and C(max) values for the antivenom as well as its longer residence time indicate that the venom and antivenom are expected to have enough opportunity to interact in the tissue compartments. Over, this study suggests that the intramuscular administration of a single dose of antivenom (2 vials each of 5ml) based on current protocol in Iran is a suitable route for the treatment of envenomation with O. doriae. Prudently, further clinical studies with similar aims need to be carried out to confirm these findings in human victims.