2026 ICD-10-CM Diagnosis Code T37.5X4APoisoning by antiviral drugs, undetermined, initial encounter
T37.5X4A is a billable ICD-10-CM diagnosis code for poisoning by antiviral drugs, 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 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. 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
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 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
Acyclovir
a guanosine analog that acts as an antimetabolite. viruses are especially susceptible. used especially against herpes.Valacyclovir
a prodrug of acyclovir that is used in the treatment of herpes zoster and herpes simplex virus infection of the skin and mucous membranes, including genital herpes.Inosine Pranobex
an alkylamino-alcohol complex of inosine used in the treatment of a variety of viral infections. unlike other antiviral agents, it acts by modifying or stimulating cell-mediated immune processes rather than acting on the virus directly.Methisazone
an antiviral agent effective against pox viruses.Ribavirin
a nucleoside antimetabolite antiviral agent that blocks nucleic acid synthesis and is used against both rna and dna viruses.Rimantadine
an rna synthesis inhibitor that is used as an antiviral agent in the prophylaxis and treatment of influenza.Thymopentin
synthetic pentapeptide corresponding to the amino acids 32-36 of thymopoietin and exhibiting the full biological activity of the natural hormone. it is an immunomodulator which has been studied for possible use in the treatment of rheumatoid arthritis, aids, and other primary immunodeficiencies.Trifluridine
an antiviral derivative of thymidine used mainly in the treatment of primary keratoconjunctivitis and recurrent epithelial keratitis due to herpes simplex virus. (from martindale, the extra pharmacopoeia, 30th ed, p557)Vidarabine
a nucleoside antibiotic isolated from streptomyces antibioticus. it has some antineoplastic properties and has broad spectrum activity against dna viruses in cell cultures and significant antiviral activity against infections caused by a variety of viruses such as the herpes viruses, the vaccinia virus and varicella zoster virus.Vidarabine Phosphate
an adenosine monophosphate analog in which ribose is replaced by an arabinose moiety. it is the monophosphate ester of vidarabine with antiviral and possibly antineoplastic properties.Zalcitabine
a dideoxynucleoside compound in which the 3'-hydroxy group on the sugar moiety has been replaced by a hydrogen. this modification prevents the formation of phosphodiester linkages which are needed for the completion of nucleic acid chains. the compound is a potent inhibitor of hiv replication at low concentrations, acting as a chain-terminator of viral dna by binding to reverse transcriptase. its principal toxic side effect is axonal degeneration resulting in peripheral neuropathy.Zidovudine
a dideoxynucleoside compound in which the 3'-hydroxy group on the sugar moiety has been replaced by an azido group. this modification prevents the formation of phosphodiester linkages which are needed for the completion of nucleic acid chains. the compound is a potent inhibitor of hiv replication, acting as a chain-terminator of viral dna during reverse transcription. it improves immunologic function, partially reverses the hiv-induced neurological dysfunction, and improves certain other clinical abnormalities associated with aids. its principal toxic effect is dose-dependent suppression of bone marrow, resulting in anemia and leukopenia.
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 T37.5X4A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T37.5X4AOverview
Is T37.5X4A (Poisoning by antiviral drugs, undetermined) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by antiviral drugs, undetermined, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T37.5X4A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by antiviral drugs, undetermined, such as an emergency visit or first evaluation.
What MS-DRG does T37.5X4A group to?
When poisoning by antiviral drugs, undetermined, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of T37.5X4A?
Under the General Equivalence Mappings, poisoning by antiviral drugs, undetermined, initial encounter converts to ICD-9-CM 961.7 (poisoning-antiviral drug) and E980.4 (undet pois-med agnt NEC). The mapping is approximate, so confirm the match fits the documentation.
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.
