2026 ICD-10-CM Diagnosis Code T36.2X6AUnderdosing of chloramphenicol group, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T36

ICD-10-CM T36.2X6A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T36.2X6A is a billable ICD-10-CM diagnosis code for underdosing of chloramphenicol group, 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). The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T36.2X6A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of chloramphenicol group, initial encounter
Short Description
Underdosing of chloramphenicol group, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T36.2X6
Underdosing of chloramphenicol group

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 CodeT36.2X6AUnderdosing of chloramphenicol group, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T36.2X6A.

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

Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.

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.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ029
Underdosing of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Chloramphenicol

    an antibiotic first isolated from cultures of streptomyces venequelae in 1947 but now produced synthetically. it has a relatively simple structure and was the first broad-spectrum antibiotic to be discovered. it acts by interfering with bacterial protein synthesis and is mainly bacteriostatic. (from martindale, the extra pharmacopoeia, 29th ed, p106)

  • Chloramphenicol O-Acetyltransferase

    an enzyme that catalyzes the acetylation of chloramphenicol to yield chloramphenicol 3-acetate. since chloramphenicol 3-acetate does not bind to bacterial ribosomes and is not an inhibitor of peptidyltransferase, the enzyme is responsible for the naturally occurring chloramphenicol resistance in bacteria. the enzyme, for which variants are known, is found in both gram-negative and gram-positive bacteria. ec 2.3.1.28.

  • Chloramphenicol Resistance

    nonsusceptibility of bacteria to the action of chloramphenicol, a potent inhibitor of protein synthesis in the 50s ribosomal subunit where amino acids are added to nascent bacterial polypeptides.

  • Thiamphenicol

    a methylsulfonyl analog of chloramphenicol. it is an antibiotic and immunosuppressive agent.

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
ChloramphenicolT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloramphenicol::ENT agentT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloramphenicol::ophthalmic preparationT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloramphenicol::topical NECT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
ChloromycetinT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloromycetin::ENT agentT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloromycetin::ophthalmic preparationT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloromycetin::otic solutionT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
Chloromycetin::topical NECT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
ClopononeT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
CloramfenicolT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6
ThiamphenicolT36.2X1T36.2X2T36.2X3T36.2X4T36.2X5T36.2X6

Patient EducationClinical

Antibiotics

Antibiotics are medicines that fight bacterial infections in people and animals. They work by killing the bacteria or by making it hard for the bacteria to grow and multiply.

The full article covers:

  • What are antibiotics?
  • What do antibiotics treat?
  • Do antibiotics treat viral infections?
  • What are the side effects of antibiotics?
  • Why is it important to take antibiotics only when they're needed?
  • How do I use antibiotics correctly?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert T36.2X6A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
No Map There is no ICD-9 equivalent for this code.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T36.2X6AOverview

Is T36.2X6A (Underdosing of chloramphenicol group) a billable code?

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

What does the 7th character A in T36.2X6A mean?

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

Can T36.2X6A be a principal diagnosis?

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

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.