2026 ICD-10-CM Diagnosis Code T36.8X6AUnderdosing of other systemic antibiotics, initial encounter
T36.8X6A is a billable ICD-10-CM diagnosis code for underdosing of other systemic 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). 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
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T36.8X6A.
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.
Clinical InformationClinical
Capreomycin
cyclic peptide antibiotic similar to viomycin. it is produced by streptomyces capreolus.Ciprofloxacin
a broad-spectrum antimicrobial carboxyfluoroquinoline.Clindamycin
an antibacterial agent that is a semisynthetic analog of lincomycin.Colistin
cyclic polypeptide antibiotic from bacillus colistinus. it is composed of polymyxins e1 and e2 (or colistins a, b, and c) which act as detergents on cell membranes. colistin is less toxic than polymyxin b, but otherwise similar; the methanesulfonate is used orally.Enoxacin
a broad-spectrum 6-fluoronaphthyridinone antibacterial agent that is structurally related to nalidixic acid.Enviomycin
cyclic basic peptide related to viomycin. it is isolated from an induced mutant of streptomyces griseoverticillatus var. tuberacticus and acts as an antitubercular agent with less ototoxicity than tuberactinomycin.Fleroxacin
a broad-spectrum antimicrobial fluoroquinolone. the drug strongly inhibits the dna-supercoiling activity of dna gyrase.Fosfomycin
an antibiotic produced by streptomyces fradiae.Fusidic Acid
an antibiotic isolated from the fermentation broth of fusidium coccineum. (from merck index, 11th ed). it acts by inhibiting translocation during protein synthesis.Lincomycin
an antibiotic produced by streptomyces lincolnensis var. lincolnensis. it has been used in the treatment of staphylococcal, streptococcal, and bacteroides fragilis infections.Norfloxacin
a synthetic fluoroquinolone (fluoroquinolones) with broad-spectrum antibacterial activity against most gram-negative and gram-positive bacteria. norfloxacin inhibits bacterial dna gyrase.Levofloxacin
the l-isomer of ofloxacin.Ofloxacin
a synthetic fluoroquinolone antibacterial agent that inhibits the supercoiling activity of bacterial dna gyrase, halting dna replication.Ristocetin
an antibiotic mixture of two components, a and b, obtained from nocardia lurida (or the same substance produced by any other means). it is no longer used clinically because of its toxicity. it causes platelet agglutination and blood coagulation and is used to assay those functions in vitro.von Willebrand Factor
a high-molecular-weight plasma protein, produced by endothelial cells and megakaryocytes, that is part of the factor viii/von willebrand factor complex. the von willebrand factor has receptors for collagen, platelets, and ristocetin activity as well as the immunologically distinct antigenic determinants. it functions in adhesion of platelets to collagen and hemostatic plug formation. the prolonged bleeding time in von willebrand diseases is due to the deficiency of this factor.Teicoplanin
lipoglycopeptide antibiotic from actinoplanes teichomyceticus active against gram-positive bacteria. it consists of five major components each with a different fatty acid moiety.Vancomycin
antibacterial obtained from streptomyces orientalis. it is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear.Vancomycin Resistance
nonsusceptibility of bacteria to the action of vancomycin, an inhibitor of cell wall synthesis.Vancomycin-Resistant Enterococci
strains of the genus enterococcus that are resistant to the antibiotic vancomycin. the enterococci become resistant by acquiring plasmids carrying genes for vancomycin resistance.Vancomycin-Resistant Staphylococcus aureus
isolates of the staphylococcus aureus that are resistant to the antibiotic vancomycin. the s. aureus becomes resistant by acquiring plasmids carrying genes for vancomycin resistance. vancomycin‐intermediate s. aureus has low-level vancomycin resistance requiring an intermediate concentration of vancomycin between sensitive and resistant isolates. these s. aureus with reduced susceptibility to vancomycin and related glycopeptide antibiotics are often seen in healthcare associated infections.Viomycin
a strongly basic peptide, antibiotic complex from several strains of streptomyces. it is allergenic and toxic to kidneys and the labyrinth. viomycin is used in tuberculosis as several different salts and in combination with other agents.Streptogramin A
a specific streptogramin group a antibiotic produced by streptomyces graminofaciens and other bacteria.Virginiamycin
a cyclic polypeptide antibiotic complex from streptomyces virginiae, s. loidensis, s. mitakaensis, s. pristina-spiralis, s. ostreogriseus, and others. it consists of 2 major components, virginiamycin factor m1 and virginiamycin factor s1. it is used to treat infections with gram-positive organisms and as a growth promoter in cattle, swine, and poultry.
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
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 T36.8X6A to ICD-9-CMHistory
Code History & ChangesHistory
Replaced This code was replaced in the FY 2026 code set by:
- T36.AX6A - Underdosing of fluoroquinolone antibiotics, init
- T36.AX6A - Underdosing of fluoroquinolone antibiotics, init
Questions About T36.8X6AOverview
Is T36.8X6A (Underdosing of other systemic antibiotics) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other systemic antibiotics, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T36.8X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other systemic antibiotics, such as an emergency visit or first evaluation.
Can T36.8X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other systemic antibiotics, 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.
