The invention provides a strategy for site specific covalent modification of antibodies using a specialized targeting covalent heterobivalent ligand (cHBL), and corresponding design for a covalent heterobivalent inhibitor (cHBI) that can be used to prevent Immunoglobulin E (IgE) mediated allergic reactions triggered by drug molecules, according to one embodiment. These molecules contain four important components: (1) an IgE antigen binding site (ABS) ligand that can be a mimotope for the allergen protein, a small molecule, or a peptidomimetic, (2) an appropriate linker, which can be any flexible or rigid chemical linker, providing spacing between the ABS binder and the other moieties, (3) a nucleotide binding site (NBS) ligand, and (4) a reactive moiety to form a covalent link with an amino acid side chain of target IgE antibodies.