2026 ICD-10-CM Diagnosis Code T37.8X6AUnderdosing of other specified systemic anti-infectives and antiparasitics, initial encounter
T37.8X6A is a billable ICD-10-CM diagnosis code for underdosing of other specified systemic anti-infectives and antiparasitics, 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 T37.8X6A.
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 other systemic anti-infectives and antiparasitics (T37). 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
Bithionol
halogenated anti-infective agent that is used against trematode and cestode infestations.Cinoxacin
synthetic antimicrobial related to oxolinic acid and nalidixic acid and used in urinary tract infections.Clioquinol
a potentially neurotoxic 8-hydroxyquinoline derivative long used as a topical anti-infective, intestinal antiamebic, and vaginal trichomonacide. the oral preparation has been shown to cause subacute myelo-optic neuropathy and has been banned worldwide.Fluconazole
triazole antifungal agent that is used to treat oropharyngeal candidiasis and cryptococcal meningitis in aids.Flucytosine
a fluorinated cytosine analog that is used as an antifungal agent.Furazolidone
a nitrofuran derivative with antiprotozoal and antibacterial activity. furazolidone acts by gradual inhibition of monoamine oxidase. (from martindale, the extra pharmacopoeia, 30th ed, p514)Hexetidine
a bactericidal and fungicidal antiseptic. it is used as a 0.1% mouthwash for local infections and oral hygiene. (from martindale, the extra pharmacopoeia, 30th ed, p797)Hydroxychloroquine
a chemotherapeutic agent that acts against erythrocytic forms of malarial parasites. hydroxychloroquine appears to concentrate in food vacuoles of affected protozoa. it inhibits plasmodial heme polymerase. (from gilman et al., goodman and gilman's the pharmacological basis of therapeutics, 9th ed, p970)Iodoquinol
one of the halogenated 8-quinolinols widely used as an intestinal antiseptic, especially as an antiamebic agent. it is also used topically in other infections and may cause cns and eye damage. it is known by very many similar trade names world-wide.Itraconazole
a triazole antifungal agent that inhibits cytochrome p-450-dependent enzymes required for ergosterol synthesis.Diatrizoate Meglumine
a versatile contrast medium used for diagnostic x-ray radiology.Iothalamate Meglumine
a radiopaque medium used for urography, angiography, venography, and myelography. it is highly viscous and binds to plasma proteins.Ioxaglic Acid
a low-osmolar, ionic contrast medium used in various radiographic procedures.Meglumine
1-deoxy-1-(methylamino)-d-glucitol. a derivative of sorbitol in which the hydroxyl group in position 1 is replaced by a methylamino group. often used in conjunction with iodinated organic compounds as contrast medium.Meglumine Antimoniate
antimony salt of meglumine that is used in the treatment of leishmaniasis.Metronidazole
a nitroimidazole used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections.Nalidixic Acid
a synthetic 1,8-naphthyridine antimicrobial agent with a limited bacteriocidal spectrum. it is an inhibitor of the a subunit of bacterial dna gyrase.Nifuratel
local antiprotozoal and antifungal agent that may also be given orally.Nitrofurantoin
a urinary anti-infective agent effective against most gram-positive and gram-negative organisms. although sulfonamides and antibiotics are usually the agents of choice for urinary tract infections, nitrofurantoin is widely used for prophylaxis and long-term suppression.Oxolinic Acid
synthetic antimicrobial related to nalidixic acid and used in urinary tract infections.Pefloxacin
a synthetic broad-spectrum fluoroquinolone antibacterial agent active against most gram-negative and gram-positive bacteria.Pipemidic Acid
antimicrobial against gram negative and some gram positive bacteria. it is protein bound and concentrated in bile and urine and used for gastrointestinal, biliary, and urinary infections.Piromidic Acid
antibacterial against mainly gram negative organisms. it is used for urinary tract and intestinal infections.Trimethoprim
a pyrimidine inhibitor of dihydrofolate reductase, it is an antibacterial related to pyrimethamine. it is potentiated by sulfonamides and the trimethoprim, sulfamethoxazole drug combination is the form most often used. it is sometimes used alone as an antimalarial. trimethoprim resistance has been reported.Trimethoprim Resistance
nonsusceptibility of bacteria to the action of trimethoprim.Trimethoprim, Sulfamethoxazole Drug Combination
a drug combination with broad-spectrum antibacterial activity against both gram-positive and gram-negative organisms. it is effective in the treatment of many infections, including pneumocystis pneumonia in aids.
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
Medication Errors
Medicines treat infectious diseases, prevent problems from chronic diseases, and ease pain. But medicines can also cause harmful reactions if not used correctly. Errors can happen in the hospital, at the health care provider's office, at the pharmacy, or at home. You can help prevent errors by:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T37.8X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T37.8X6AOverview
Is T37.8X6A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other specified systemic anti-infectives and antiparasitics, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T37.8X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other specified systemic anti-infectives and antiparasitics, such as an emergency visit or first evaluation.
Can T37.8X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other specified systemic anti-infectives and antiparasitics, 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.
