Premedication
The issue of premedication prior to the administration of antivenoms has been controversial. However, a recent publication from Sri Lanka provides good evidence from a randomised controlled trial that premedication with subcutaneous adrenaline reduced the rate of allergic reactions to snake antivenom from 43% (placebo) to 11% ( adrenaline). There were reported to be no adverse effects related to the use of adrenaline. (Premawardhena et al., BMJ 318: 1041-1043, 17 April 1999). Premedication with subcutaneous adrenaline is currently recommended prior to the intravenous administration of Australian snake antivenoms. Adults should receive 0.25-0.3mg of adrenaline by the subcutaneous route (0.005-0.01 mg/kg for a child). Adrenaline as a premedicant should never be given intravenously, in order to avoid hypertension in the coagulopathic patient with the potential for bleeding. Similarly, it should not be administered intramuscularly, as this may also lead to hypertension, as well as to haematoma formation in the presence of coagulopathy.
Although traditional, the role of antihistamines in premedication is unclear. There is some overseas evidence to suggest that the incidence of allergic reactions to snake antivenom is not reduced by antihistamine. In addition, the only currently available parenteral antihistamine in Australia, promethazine, has sedative effects which may be undesirable in envenomed patients.
Last updated: July 2005
