A patient accidentally takes twice the prescribed dose of warfarin and develops gastrointestinal bleeding.

Taking more medication than prescribed constitutes poisoning under ICD-10-CM drug-event rules. The drug may have been correctly prescribed, but the patient took an incorrect amount.

For poisoning, the applicable poisoning code is generally sequenced first, followed by codes identifying manifestations such as gastrointestinal bleeding.

This differs from an adverse effect, in which a drug is correctly prescribed and properly administered but causes an undesirable reaction. In adverse-effect scenarios, the nature of the adverse effect is coded first, followed by the drug code with the appropriate adverse-effect character.

Underdosing applies when the patient takes less of a medication than prescribed, whether intentionally or unintentionally. It does not describe excessive dosing.

For CDI specialists, determining whether an event represents poisoning, adverse effect, or underdosing requires careful review of how the medication was prescribed and actually taken. Phrases such as “warfarin-related bleeding” may not always provide enough information to determine the correct classification.

A clarification query may therefore be appropriate when dose, intent, or medication-use circumstances are unclear.

CCDS Reference Topics: Poisoning; adverse effects; underdosing; medication events; sequencing.

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