2026 ICD-10-CM Diagnosis Code T36.AX5AAdverse effect of fluoroquinolone antibiotics, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T36

ICD-10-CM T36.AX5A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T36.AX5A is a billable ICD-10-CM diagnosis code for adverse effect of fluoroquinolone antibiotics, 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 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor.

Code Identity

ICD-10-CM Code
T36.AX5A
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of fluoroquinolone antibiotics, initial encounter
Short Description
Adverse effect of fluoroquinolone antibiotics, init
Parent Code
T36.AX5
Adverse effect of fluoroquinolone antibiotics

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT36Poisoning by, adverse effect of and underdosing of systemic antibiotics
This CodeT36.AX5AAdverse effect of fluoroquinolone antibiotics, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T36.AX5A.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Coding GuidelinesGuidance

When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.

The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of systemic antibiotics (T36). 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 2026, published by CMS and the National Center for Health Statistics.

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.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Fluoroquinolone antibioticsT36.AX1T36.AX2T36.AX3T36.AX4T36.AX5T36.AX6

Code History & ChangesHistory

New Code T36.AX5A was added to the ICD-10-CM code set for FY 2026, effective October 1, 2025.

Replacement T36.AX5A replaces the following previously assigned code(s):

  • T36.8X5A - Adverse effect of other systemic antibiotics, init encntr
FY 2026AddedAdded to the ICD-10-CM code setEffective October 1, 2025.
FY 2026CurrentRevised in the current code setEffective October 1, 2025 through September 30, 2026.

Questions About T36.AX5AOverview

Is T36.AX5A (Adverse effect of fluoroquinolone antibiotics) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of fluoroquinolone antibiotics, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T36.AX5A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of fluoroquinolone antibiotics, such as an emergency visit or first evaluation.

What MS-DRG does T36.AX5A group to?

On inpatient claims, adverse effect of fluoroquinolone antibiotics, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T36.AX5A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of fluoroquinolone antibiotics, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.