Neutralizing Efficacy of Expired Snake Antivenoms: A Systematic Review of Preclinical Studies and Real-World Experience

OBJECTIVES: This study aimed to systematically review and summarize the sparse preclinical evidence of neutralizing efficacy of expired antivenoms and real-world experience of using expired antivenoms in humans.

METHODS: We searched for articles published until 1 March 2023 in PubMed, Scopus, Web of Science, and Embase. All studies demonstrating the neutralizing efficacy of expired antivenoms against snake venoms or studies describing the real-world experience of using expired antivenoms were included. Narrative data synthesis was applied to summarize the efficacy of expired antivenoms from all included studies.

RESULTS: Fifteen studies were included, of which ten were preclinical studies and five were articles describing the real-world experience of using expired antivenoms in humans. The expired duration of antivenoms in the included studies ranged from two months to 20 years. The quality of expired antivenoms was evaluated in one included study and they met the standard quality tests. Five studies demonstrated that the expired antivenoms' immunological concentration and venom-binding activity were comparable to non-expired ones but could gradually deteriorate after expiration. The findings from preclinical studies and real-world experience of using expired antivenoms in humans consistently exhibited that expired antivenoms, compared to non-expired antivenoms, were effective when stored in proper storage conditions. Nonetheless, the safety profiles of expired antivenoms were limited and could not be summarized in this study.

CONCLUSIONS: Expired antivenoms are feasible as a short-term solution to save the lives of severely envenoming victims when non-expired antivenoms are not accessible. Therefore, we encourage manufacturers to extend the antivenom expiry date according to the results of the stability tests.