ICD-10-CM > S00-T88 > T36-T50 > T42 > T42.0 > T42.0X > T42.0X6 T42.0X6 Underdosing of hydantoin derivatives Non-Billable/Non-Specific Codes T42.0X6A..., initial encounterT42.0X6D..., subsequent encounterT42.0X6S..., sequela