A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom

Abstract

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Widow spider antivenoms, including redback spider antivenom, are often given by the intramuscular route. • No studies have measured widow spider antivenom following intramuscular or intravenous antivenom. WHAT THIS STUDY ADDS • Intramuscular redback spider antivenom is not detectable in serum for at least 3–5 h after treatment. Intravenous antivenom is detectable 30 min after intravenous infusion. • Intramuscular antivenom may not be an effective administration route. AIMS There are no studies measuring antivenom concentrations following intramuscular administration. This study aimed to compare antivenom concentrations following intravenous and intramuscular administration of redback spider antivenom (RBSAV). METHODS Twenty patients recruited to a controlled trial comparing intramuscular and intravenous administration of antivenom had serial blood samples collected at 30 min intervals for 2 h after the administration of one or two doses of antivenom. Antivenom concentration was measured using an enzyme immunoassay. RESULTS Ten patients received intramuscular antivenom but antivenom could not be detected in serum after either one or two vials, at any time point. The median time of the final sample after commencement of antivenom treatment in these patients was 3.2 h (1.8–5 h). Ten patients received intravenous antivenom (three one vial and seven two or more vials) and antivenom was detected in all patients. CONCLUSIONS RBS AV given by the intramuscular route is unlikely to be effective in the treatment of redback (widow) spider bite.

Pharmacokinetics of a F(ab′)2 scorpion antivenom administered intramuscularly in healthy human volunteers

“…In spite of anecdotal references to successful treatment of poisonings using antivenoms via IM injection, there is a wealth of clinical evidence suggesting that this route is unreliable [3][4][5][6][7][8]. Still, there was no quantitative pharmacokinetic data on IM F(ab′) 2 .…”

“…Still, a question often posed by laypersons, paramedics and clinicians is: What to do if the use of the IV route is not available due to the lack of skill, distance from hospitals or situations such as in infants? Several recent publications suggest that when the intramuscular (im) route is used, antivenoms are poorly effective [3][4][5][6][7][8]. There is information on F(ab′) 2 antiscorpion pharmacokinetics in humans after a bolus of antivenom is given [9], but there is no information on antivenoms used in humans by any other route.…”

Randomized Controlled Trial of Intravenous Antivenom Versus Placebo for Latrodectism: The Second Redback Antivenom Evaluation (RAVE-II) Study

“…In addition, a pharmacokinetic analysis of a subgroup of patients from one trial found that antivenom was only detectable in serum after intravenous administration. 13 A small phase II study of black widow spider antivenom versus placebo found no significant benefit of antivenom over placebo. 12 Taken together, these results suggested that antivenom might be no more effective than placebo and provided sufficient doubt to warrant a placebo-controlled trial.…”

Editors' view January 2008

“…The authorship of this present number spans North America, continental Europe, Africa and Australasia. There are papers on human toxicology [2] and on prescribing [3], and papers on large molecular weight biologicals including an overview of studies of recombinant activated factor VII [4] and the first PK‐PD study modelling the effect of antilymphocyte globulin in kidney transplant patients [5]. There is also a satisfying diversity of experimental methodologies.…”