2026 ICD-10-CM Diagnosis Code T37.5X5AAdverse effect of antiviral drugs, initial encounter
T37.5X5A is a billable ICD-10-CM diagnosis code for adverse effect of antiviral drugs, 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T37.5X5A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Aciclovir adverse reaction
- Adverse reaction to bebtelovimab
- Adverse reaction to casirivimab
- Adverse reaction to casirivimab and/or imdevimab
- Adverse reaction to dimethyl sulfoxide and/or idoxuridine
- Adverse reaction to imdevimab
- Adverse reaction to interferon gamma-1b
- Adverse reaction to remdesivir
- Adverse reaction to sotrovimab
- Anemia caused by zidovudine
- Antiviral drug adverse reaction
- Cidofovir-induced anterior uveitis
- Didanosine adverse reaction
- Disorder of cellular component of blood caused by antiretroviral drug
- Disorder of gastrointestinal tract caused by antiretroviral drug
- Drug-induced uveitis
- Eruption of skin caused by antiretroviral drug
- Famciclovir adverse reaction
- Foscarnet adverse reaction
- Ganciclovir adverse reaction
- Idoxuridine adverse reaction
- Indinavir urolithiasis
- Inosine pranobex adverse reaction
- Interferon-A-2a adverse reaction
- Interferon-A-2b adverse reaction
- Interferon-A-N1 adverse reaction
- Interferons adverse reaction
- Lipoatrophy caused by antiretroviral drug
- Lipodystrophy caused by antiretroviral drug
- Nodular hyperplasia of liver
- Nodular regenerative hyperplasia of liver
- Nodular regenerative hyperplasia of liver caused by antiretroviral drug
- Nodule of liver
- Phlebosclerosis
- Portal and splenic vein sclerosis
- Portal hypertension
- Portal hypertension caused by antiretroviral drug
- Sclerosis of portal vein and splenic vein caused by antiretroviral drug
- Sleep disorder caused by reverse transcriptase inhibitor
- Steatosis of liver caused by retroviral protease inhibitor
- Tribavirin adverse reaction
- Trifluorothymidine adverse reaction
- Valaciclovir adverse reaction
- Venous hypertension
- Vidarabine adverse reaction
- Zalcitabine adverse reaction
- Zidovudine adverse reaction
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 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
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T37.5X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T37.5X5AOverview
Is T37.5X5A (Adverse effect of antiviral drugs) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of antiviral drugs, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T37.5X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of antiviral drugs, such as an emergency visit or first evaluation.
What MS-DRG does T37.5X5A group to?
On inpatient claims, adverse effect of antiviral drugs, 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 T37.5X5A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of antiviral drugs, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
What is the ICD-9 equivalent of T37.5X5A?
Under the General Equivalence Mappings, adverse effect of antiviral drugs, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E931.7 (adv eff antiviral drugs). 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.
