Underdosing of hydantoin derivatives, subsequent encounter

This code indicates that a patient is experiencing adverse effects or complications because they have not taken enough of their prescribed hydantoin derivative medication, such as phenytoin. This underdosing is occurring during a follow-up visit for the initial problem or for ongoing management of the underdosing itself.

Use this code when documenting a patient presenting for a return visit where their hydantoin levels are subtherapeutic, leading to uncontrolled seizures or other symptoms due to insufficient medication intake. It is appropriate for situations where the underdosing is being actively managed or monitored after initial identification.

• Ensure documentation clearly states the underdosing is the cause of the patient's current condition and that this is a subsequent encounter.
• Always code the specific adverse effect or complication of the underdosing first, followed by this underdosing code.
• Distinguish from initial encounters (A) or sequelae (S) by verifying the encounter type in the medical record.