Crotalidae polyvalent immune Fab (Crofab)

From WikEM
Jump to: navigation, search

Background

  • The original Antivenin Crotalidae Polyvalent (ACP)[1] was manufactured by Wyeth Pharmaceutical for use in the US but due to severe delayed allergic reactions was discontinued.
  • The FDA approved Crofab, an antivenom derived from sheep serum[2] in 2000. The antibodies bind and neutralize venom components.

Synthesis and Production

  • Produced from sheep serum after inoculation with venom from:
    • Eastern diamondback rattlesnake (Crotalus adamants)
    • Western diamondback rattlesnake (Crotalus atria)
    • Mojave rattlesnake (Crotalus scutulatus).
    • Cottonmouth (Agkistrodon piscivorus)
  • The Fc portion of the antibody is eliminated after mixture with papain and subsequent purification.

Indications for Administration of CroFab[3]

  • Progression of swelling
  • Abnormal results on lab tests (platelets < 100,000 or fibrinogen < 100)
  • Systemic manifestations (unstable vitals or altered mental status)

Dosing and Administration

Initial Administration

  • Initial dose: 6 vials[4]
  • Typically diluted into 250 cc or 1 L of normal saline and infused over an hour
  • Same dose for both adults and pediatrics (may have to adjust the dilution of CroFab for small children so that they are not volume overloaded)

Maintenance therapy

  • May repeat dose (2 vials) at 6, 12, and 18 hours later if symptoms not controlled[5]
    • Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.[6]

Envenomation control measurement

  • Observe for progression of envenomation during and after antivenom infusion
  • Measure limb circumference at several sites above and below bite
  • Mark advancing border of edema q30min
  • Repeat labs q4hr or after each course of antivenom (whichever is more frequent)

Side Effects

  • Acute allergic reactions occur in <10% pts
    • If occurs stop infusion and give epinephrine/antihistamines if needed
  • Recurrent thrombocytopenia has been described up to 2 weeks after transfusion with FabAV and is likely a result of isolated renal clearance of FabAV and persistent presence of actual venom in serum.[7]
    • Warrants close monitoring of platelets by primary physician or return visit after discharge
  • Serum sickness is unlikely but precautions should be given to patents upon discharge

See Also

References

  1. Howland MA, Smilkstein MJ. Primer on immunology with applications to toxicology. Contemp Manage Crit Care. 1991;1:109–145.
  2. Ruha AM et al: Initial postmarketing experience with crotalidae polyvalent immune Fab for treatment of rattlesnake envenomation. Ann Emerg Med. 2002;39:609–615.
  3. Dart RC et al. Efficacy of post envenomation administration of antivenin. Toxicon. 1988;26:1218–1221.
  4. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  5. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  6. Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
  7. Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.