2027 ICD-10-CM Diagnosis Code T43.3X4APoisoning by phenothiazine antipsychotics and neuroleptics, undetermined, initial encounter
T43.3X4A is a billable ICD-10-CM diagnosis code for poisoning by phenothiazine antipsychotics and neuroleptics, undetermined, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 917 through 918. Coders also document this condition as pericyazine poisoning. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, undetermined; External cause codes: poisoning by drug; and Poisoning by drugs, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Pericyazine poisoning
Coding GuidelinesGuidance
When coding a poisoning or reaction to the improper use of a medication (e.g., overdose, wrong substance given or taken in error, wrong route of administration), first assign the appropriate code from categories T36-T50. The poisoning codes have an associated intent as their 5th or 6th character (accidental, intentional self-harm, assault and undetermined). If the intent of the poisoning is unknown or unspecified, code the intent as accidental intent. The undetermined intent is only for use if the documentation in the record specifies that the intent cannot be determined. Use additional code(s) for all manifestations of poisonings.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified (T43). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T43.3X4A: its own notes plus those printed at T43, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- adverse effect of correct substance properly administered
- poisoning by overdose of substance
- poisoning by wrong substance given or taken in error
- underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T43
- Ainitial encounter this code
- Dsubsequent encounter
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T43.3X4A, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming T43.3X4A: they are not reported together with it, unless the two conditions are unrelated.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Poisoning
A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T43.3X4A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T43.3X4AOverview
Is T43.3X4A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by phenothiazine antipsychotics and neuroleptics, undetermined, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in T43.3X4A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by phenothiazine antipsychotics and neuroleptics, undetermined, such as an emergency visit or first evaluation.
What MS-DRG does T43.3X4A group to?
When poisoning by phenothiazine antipsychotics and neuroleptics, undetermined, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 918, 917, with relative weights from 0.8716 to 1.5698 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T43.3X4A be reported with a code from O29.3?
Not as a rule. The Excludes1 note at block T36-T50, which applies to T43.3X4A, lists "toxic reaction to local anesthesia in pregnancy (O29.3-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What is the ICD-9 equivalent of T43.3X4A?
Under the General Equivalence Mappings, poisoning by phenothiazine antipsychotics and neuroleptics, undetermined, initial encounter converts to ICD-9-CM 969.1 (pois-phenothiazine tranq) and E980.3 (undeterm pois-psychotrop). The mapping is approximate, so confirm the match fits the documentation.
