Adverse effect of hydantoin derivatives, initial encounter

This code signifies an undesirable or harmful reaction experienced by a patient due to the therapeutic use of a hydantoin derivative medication, such as phenytoin. These adverse effects are not due to overdose or poisoning, but rather an unexpected or unintended response to a correctly prescribed and administered dose. The "initial encounter" designation indicates that the patient is receiving active treatment for the adverse effect.

Apply this code when a patient presents for the first time for treatment of an adverse reaction to a hydantoin derivative, such as a rash, gingival hyperplasia, or neurological symptoms, when the drug was taken as prescribed. This would be used, for example, when a patient is admitted to the hospital or seen in an emergency department for evaluation and management of a newly developed adverse effect from phenytoin.

• Always sequence the adverse effect code first, followed by codes for the specific manifestation(s) of the adverse effect.
• Ensure documentation clearly distinguishes between an adverse effect (therapeutic use) and poisoning (overdose or wrong substance).
• Verify the encounter type (initial, subsequent, sequela) based on the patient's treatment for the adverse effect.