Adverse effect of antidotes and chelating agents, init

This code signifies a patient experiencing an unintended and harmful reaction to a substance administered to counteract a poison or to remove heavy metals from the body. These reactions are not due to an overdose or poisoning by the antidote/chelating agent itself, but rather an adverse physiological response at therapeutic doses.

Use this code when documenting conditions such as anaphylaxis to Narcan, nephrotoxicity from deferoxamine, or cardiac arrhythmias following administration of calcium gluconate for hyperkalemia, provided these agents were given to treat a poisoning or chelate a substance. This applies when the patient is receiving active treatment for the adverse effect.

• Always sequence this code after the code for the specific adverse effect (e.g., T78.0X for anaphylactic shock).
• Ensure the documentation clearly states the antidote or chelating agent was the cause of the adverse effect, not an overdose or poisoning by the agent itself.
• Verify the encounter is "initial" for the adverse effect; subsequent encounters would use T50.6X5D or T50.6X5S.