Crotalidae polyvalent immune Fab (Crofab)
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
Pregnancy category C
See Also
References
- ↑ Howland MA, Smilkstein MJ. Primer on immunology with applications to toxicology. Contemp Manage Crit Care. 1991;1:109–145.
- ↑ Ruha AM et al: Initial postmarketing experience with crotalidae polyvalent immune Fab for treatment of rattlesnake envenomation. Ann Emerg Med. 2002;39:609–615.
- ↑ Dart RC et al. Efficacy of post envenomation administration of antivenin. Toxicon. 1988;26:1218–1221.
- ↑ 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.
- ↑ 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.
- ↑ Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
- ↑ Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.