Breaking It Down: Understanding the Classification of Drug Toxicity

October 16, 2018

Breaking It Down:

Understanding the Classification of Drug Toxicity


It is no surprise as to why many coders are having a problem coding poisoning, adverse effects and under-dosing. There are multiple guidelines to apply when considering the code choices in this category thus making the coding more complicated.   Physicians do not always document the terms poisoning, overdose, adverse effect or under-dosing.

This means the coders really need to understand how to apply the guidelines to the documentation in the record. Intent has to be determined in order to apply the correct overdose code and the correct status code for under-dosing.  To add further confusion, the manifestations are coded along with the poisoning code which contradicts the basic coding guidelines on symptoms.  Finally, sequencing guidelines are not consistent and are based on the type of drug toxicity code being assigned.

In order to simplify the process, there are four main elements to think about when making a decision on how to code in this category.

A poisoning is taking too much of a medication or not administrating the medication by the correct route, whether it was prescribed, over the counter or as a result of substance abuse.  This may be either intentional or accidental   Also falling into the poisoning category is taking prescription medication that was not prescribed with a current prescribed drug or mixing current medications with alcohol.  When sequencing, the poisoning codes are sequenced first followed by any manifestations.

  • An individual poisoning code is assigned for all drugs involved.
  •  Acute conditions as a result of drug and alcohol abuse are also included in this category.

Poisoning intent is the intention of why the poisoning occurred and this is built into the poisoning code as the 5th or 6th character.  Categories include accidental, assault, suicide, and undetermined.  If there is no documentation of the intent in the record the default is accidental.  Undetermined should only be used if documentation in the record states the intent of the poisoning cannot be determined.

An adverse effect is an acute symptoms or condition that occurs as a result of taking medication as prescribed and properly administered.  The manifestations are sequenced first followed by the adverse effect drug code.  Intention is not considered for adverse effects since the drug is taken as prescribed.

Under dosing is taking less of a medication than prescribed or not taking the prescribed medication at all.  This may result in an exacerbation of the condition that the drug was prescribed to treat.  The manifestation is sequenced first followed by the Under-dosing drug code.

Under-dosing Intent: Is the intention of why the drug was not taken as prescribed.  This is a status code that is not built into the under-dosing code. Categories are intentional, intentional due to financial hardship, unintentional, and unintentional due to the patient’s age related debility

A manifestation is an acute symptom, condition, or exacerbation of a chronic condition as a result of not taking medications as prescribed, taking medication as prescribed, or as a result of drug abuse. Note that manifestations are coded in all drug toxicity categories.


Case 1

Patient presents with syncope and states he had a couple of beers soon after taking his Metoprolol as prescribed.

  • T44.7X1A Poisoning by beta-adrenoreceptor antagonists, accidental, initial encounter.
  • T51.0X1A Toxic effect of ethanol, accidental, initial encounter
  • R55   Syncope

Rationale: This is a poisoning. Although medication was taken as prescribed, the medication was taken with alcohol resulting in the acute condition of syncope.  The poisoning codes for both the medication and alcohol are sequenced first. The intent was accidental and is built into the poisoning code. The manifestation of syncope is coded last

Case 2

Patient presents with headache and dizziness. He was just started on Metoprolol for his blood pressure and has been taking this as prescribed.

  • G44.40      Drug induced headache, NEC, not intractable
  • R42             R42 Dizziness and giddiness
  • T44.7X5A   Adverse effect of beta-adrenoreceptor antagonist, initial encounter.

Rationale: This is an adverse effect.  The medication was taken exactly as prescribed.   The manifestations are the acute conditions of headache and dizziness. The manifestations are sequenced first, followed by the adverse effect drug code.

Case 3

Patient presents in hypertensive crisis. After questioning, it was found that he was only taking his blood pressure medicine a couple times a week due to the price.

  • I16.9   Hypertensive crisis, unspec
  • T44.7X6A (Underdosing of beta-adrenoreceptor antagonists, initial encounter
  • Z91.120 Patient’s intentional under-dosing of medication regimen due to financial hardship

Rationale:  This is an under-dosing.  The patient was taking less than the prescribed medication. The manifestation is the hypertensive crisis. The intent is intentional due to financial hardship.  In this case, the manifestation of hypertensive crisis is sequenced first, followed by the under-dosing drug code.  The intent is not built into the under-dosing code and is sequenced last as a status code.


Mary J. Wood, RHIT, CCS. AHIMA Approved ICD-10-CM/PCS Trainer

Internal Auditor/Educator