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T37.5X5A vs T42.8

T37.5X5A (Adverse effect of antiviral drugs, initial encounter) compared with T42.8 (Poisoning by, adverse effect of and underdosing of antiparkinsonism drugs and other central muscle-tone depressants), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes should not be reported together because T37.5X5A’s tabular entry lists T42.8 under Excludes1.

Official rule
What is different?

The conditions named and billing status.T37.5X5A is “Adverse effect of antiviral drugs, initial encounter”; T42.8 is “Poisoning by, adverse effect of and underdosing of antiparkinsonism drugs and other central muscle-tone depressants”. T42.8 is a non-billable header; T37.5X5A is billable.

Registry fact

Can these codes be reported together?

No.T37.5X5A’s entry carries an Excludes1 note covering T42.8: “amantadine (T42.8-)”. Both may be reported only when the documentation shows the two conditions are unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

Yes.T37.5X5A’s tabular entry: “amantadine (T42.8-)”. The note covers T42.8.

Official ruleGuide: Excludes1 vs Excludes2

Is one a parent or header code?

One is a header.T42.8 is a non-billable header, but T37.5X5A is not one of its subdivisions.

Registry fact

Nothing found in 3 other checks; 1 check does not apply
Is there an Excludes2 relationship?

None.Neither entry carries an Excludes2 note that names the other code. T37.5X5A carries 5 Excludes2 notes and T42.8 carries 6 Excludes2 notes covering other codes; the side-by-side table quotes them.

Official rule

Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Excludes1 — generally not reported together

Excludes1 conflict

T37.5X5A
Adverse effect of antiviral drugs, initial encounter
↔
T42.8
Poisoning by, adverse effect of and underdosing of antiparkinsonism drugs and other central muscle-tone depressants

What we found

No — do not report together.T37.5X5A carries an Excludes1 note covering T42.8: “amantadine (T42.8-)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

What to review

Report one of the two. Both may be reported only when the documentation shows the two conditions are unrelated to each other.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes1 note means the two conditions are not ordinarily reported together for the same encounter, because the classification treats them as mutually exclusive forms of the same condition. The documented exception is when the two conditions are unrelated to each other.

Source / rule

CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a

Official guidance behind these answers

  • Section I.A.12.a — Excludes1 · applies to: Excludes1

    A type 1 Excludes note is a pure excludes note. It means “NOT CODED HERE!” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition. An exception to the Excludes1 definition is the circumstance when the two conditions are unrelated to each other. If it is not clear whether the two conditions involving an Excludes1 note are related or not, query the provider. For example, code F45.8, Other somatoform disorders, has an Excludes1 note for "sleep related teeth grinding (G47.63)," because "teeth grinding" is an inclusion term under F45.8. Only one of these two codes should be assigned for teeth grinding. However psychogenic dysmenorrhea is also an inclusion term under F45.8, and a patient could have both this condition and sleep related teeth grinding. In this case, the two conditions are clearly unrelated to each other, and so it would be appropriate to report F45.8 and G47.63 together.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
T37.5X5A

Adverse effect of antiviral drugs, initial encounter

T42.8

Poisoning by, adverse effect of and underdosing of antiparkinsonism drugs and other central muscle-tone depressants

StatusDiffers
T37.5X5A
Billable
T42.8
Non-billable header

A header is not reported on a claim; a code beneath it is.

Report instead: T42.8X1A, T42.8X1D, T42.8X1S, T42.8X2A, T42.8X2D

Excludes1Differs
Only at T37.5X5A
  • amantadine (T42.8-)
  • cytarabine (T45.1-)
  • anti-infectives topically used for ear, nose and throat (T49.6-)
  • anti-infectives topically used for eye (T49.5-)
  • locally applied anti-infectives NEC (T49.0-)
Only at T42.8

No note of its own beyond the shared notes

Shared by both codes (1 note)
  • toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2Differs
Only at T37.5X5A

No note of its own beyond the shared notes

Only at T42.8
  • drug dependence and related mental and behavioral disorders due to psychoactive substance use (F10.--F19.-)
Shared by both codes (5 notes)
  • abuse and dependence of psychoactive substances (F10-F19)
  • abuse of non-dependence-producing substances (F55.-)
  • immunodeficiency due to drugs (D84.821)
  • drug reaction and poisoning affecting newborn (P00-P96)
  • pathological drug intoxication (inebriation) (F10-F19)
Code firstSame for both
  • , for adverse effects, the nature of the adverse effect, such as:
  • adverse effect NOS (T88.7)
  • aspirin gastritis (K29.-)
  • blood disorders (D56-D76)
  • contact dermatitis (L23-L25)
  • dermatitis due to substances taken internally (L27.-)
  • nephropathy (N14.0-N14.2)
Use additional codeSame for both
  • code(s) to specify:
  • manifestations of poisoning
  • underdosing or failure in dosage during medical and surgical care (Y63.6, Y63.8-Y63.9)
  • underdosing of medication regimen (Z91.12-, Z91.13-)
CategoryDiffers
T37.5X5A

T37 Poisoning by, adverse effect of and underdosing of other systemic anti-infectives and antiparasitics

T42.8

T42 Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs

ChapterSame for both

S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)

IncludesDiffers
Only at T37.5X5A

No note of its own beyond the shared notes

Only at T42.8
  • Poisoning by, adverse effect of and underdosing of amantadine
Shared by both codes (4 notes)
  • adverse effect of correct substance properly administered
  • poisoning by overdose of substance
  • poisoning by wrong substance given or taken in error
  • underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed
7th characterDiffers
T37.5X5A
  • The appropriate 7th character is to be added to each code from category T37
T42.8
  • The appropriate 7th character is to be added to each code from category T42

No Code also note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, each code’s own notes are listed under it, and the notes every code shares are listed once beneath them.

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Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources