Failure of intramuscular antivenom in Red-back spider envenoming.

Four cases of Red-back spider envenoming are reported in which there was minimal response to intramuscular antivenom. Intravenous antivenom was then administered in each case with almost complete resolution of symptoms. All cases were followed up to confirm the effect of treatment. This failure of intramuscular Red-back antivenom raises the question of its efficacy. There has been no controlled trial to prove that intramuscular Red-back antivenom is effective and animal work with other antivenoms has demonstrated the intramuscular formulation to have delayed and incomplete effects. Controlled studies should be undertaken to establish the effectiveness of intravenous and intramuscular Red-back antivenom.