Most common adverse reactions (incidence ?5% of subjects) were urticaria, rash nausea, pruritus and back pain ^{FDA label}.

Severe hypersensitivity reactions may occur with the use of CROFAB. In case of acute hypersensitivity reactions, including anaphylaxis and anaphylactoid reactions, discontinue infusion and institute appropriate emergency treatment ^{FDA label}.

CROFAB contains purified immunoglobulin fragments from the blood of sheep that have been immunized with snake venoms. Injection of heterologous animal proteins can lead to severe acute and delayed hypersensitivity reactions (late serum reaction or serum sickness) and a possible febrile response to immune complexes formed by animal antibodies and neutralized venom components.

Papain enzyme is used to cleave antibodies into fragments during the processing of CROFAB, and negligible amounts of papain or inactivated papain residues may be present. Patients allergic to papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain may also have an allergic reaction to CROFAB. Certain dust mite allergens and some latex allergens share antigenic structures with papain and patients with these allergies may be allergic to papain ^{FDA label}.