The **ICD-10-CM code** for **Theophylline toxicity (initial encounter)** is: **T41.2X1A** – Poisoning by, adverse effect of and underdosing of other general anesthetics, initial encounter However, this code is for anesthetics and **not specific to Theophylline**, which is a methylxanthine drug used for respiratory diseases. The correct code for **Theophylline toxicity** (which is considered a poisoning by methylxanthines) is: **T43.691A – Poisoning by methylxanthines, accidental (unintentional), initial encounter** You may need to adjust the 6th character for intent (accidental, intentional self-harm, assault, undetermined): - **T43.691A** – Accidental (unintentional), initial encounter - **T43.692A** – Intentional self-harm, initial encounter - **T43.693A** – Assault, initial encounter - **T43.694A** – Undetermined, initial encounter **Use additional code** to identify the manifestations of the poisoning, such as seizures or cardiac arrhythmias, if applicable. **Summary:** **Theophylline toxicity (initial encounter):** **T43.691A** (if accidental/unintentional) *Always confirm with the latest ICD-10-CM manual and your clinical documentation.*