2026 ICD-10-CM Diagnosis Code T45.0X5AAdverse effect of antiallergic and antiemetic drugs, initial encounter
T45.0X5A is a billable ICD-10-CM diagnosis code for adverse effect of antiallergic and antiemetic 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 T45.0X5A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- 5-HT3-receptor antagonist adverse reaction
- Acrivastine adverse reaction
- Adverse reaction to antihistamines
- Adverse reaction to mast cell stabilizer
- Adverse reaction to meclizine
- Adverse reaction to xanthine and/or xanthine derivative
- Antazoline adverse reaction
- Antiemetic adverse reaction
- Astemizole adverse reaction
- Azatadine adverse reaction
- Azelastine adverse reaction
- Brompheniramine adverse reaction
- Cetirizine adverse reaction
- Chlorphenamine adverse reaction
- Cinnarizine adverse reaction
- Clemastine adverse reaction
- Cough suppressant adverse reaction
- Cyclizine adverse reaction
- Cyproheptadine adverse reaction
- Dimenhydrinate adverse reaction
- Dimethindene adverse reaction
- Diphenhydramine adverse reaction
- Diphenylpyraline adverse reaction
- Domperidone adverse reaction
- H1 antihistamine adverse reaction
- Ketotifen adverse reaction
- Lodoxamide adverse reaction
- Loratadine adverse reaction
- Mebhydrolin adverse reaction
- Mepyramine adverse reaction
- Metoclopramide adverse reaction
- Oxatomide adverse reaction
- Phenindamine adverse reaction
- Pheniramine adverse reaction
- Terfenadine adverse reaction
- Triprolidine 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 primarily systemic and hematological agents, not elsewhere classified (T45). 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
Astemizole
antihistamine drug now withdrawn from the market in many countries because of rare but potentially fatal side effects.Brompheniramine
histamine h1 antagonist used in treatment of allergies, rhinitis, and urticaria.Cetirizine
a potent second-generation histamine h1 antagonist that is effective in the treatment of allergic rhinitis, chronic urticaria, and pollen-induced asthma. unlike many traditional antihistamines, it does not cause drowsiness or anticholinergic side effects.Chlorpheniramine
a histamine h1 antagonist used in allergic reactions, hay fever, rhinitis, urticaria, and asthma. it has also been used in veterinary applications. one of the most widely used of the classical antihistaminics, it generally causes less drowsiness and sedation than promethazine.Cinnarizine
a piperazine derivative having histamine h1-receptor and calcium-channel blocking activity with vasodilating and antiemetic properties but it induces parkinsonian disorders.Clemastine
a histamine h1 antagonist used as the hydrogen fumarate in hay fever, rhinitis, allergic skin conditions, and pruritus. it causes drowsiness.Cyclizine
a histamine h1 antagonist given by mouth or parenterally for the control of postoperative and drug-induced vomiting and in motion sickness. (from martindale, the extra pharmacopoeia, 30th ed, p935)Cyproheptadine
a serotonin antagonist and a histamine h1 blocker used as antipruritic, appetite stimulant, antiallergic, and for the post-gastrectomy dumping syndrome, etc.Dimenhydrinate
a drug combination that contains diphenhydramine and theophylline. it is used for treating vertigo, motion sickness, and nausea associated with pregnancy.Dimethindene
a histamine h1 antagonist. it is used in hypersensitivity reactions, in rhinitis, for pruritus, and in some common cold remedies.Diphenhydramine
a histamine h1 antagonist used as an antiemetic, antitussive, for dermatoses and pruritus, for hypersensitivity reactions, as a hypnotic, an antiparkinson, and as an ingredient in common cold preparations. it has some undesired antimuscarinic and sedative effects.Domperidone
a specific blocker of dopamine receptors. it speeds gastrointestinal peristalsis, causes prolactin release, and is used as antiemetic and tool in the study of dopaminergic mechanisms.Doxylamine
histamine h1 antagonist with pronounced sedative properties. it is used in allergies and as an antitussive, antiemetic, and hypnotic. doxylamine has also been administered in veterinary applications and was formerly used in parkinsonism.Granisetron
a serotonin receptor (5ht-3 selective) antagonist that has been used as an antiemetic for cancer chemotherapy patients.Ketotifen
a cycloheptathiophene blocker of histamine h1 receptors and release of inflammatory mediators. it has been proposed for the treatment of asthma, rhinitis, skin allergies, and anaphylaxis.Methapyrilene
histamine h1 antagonist with sedative action used as a hypnotic and in allergies.Metoclopramide
a dopamine d2 antagonist that is used as an antiemetic.Ondansetron
a competitive serotonin type 3 receptor antagonist. it is effective in the treatment of nausea and vomiting caused by cytotoxic chemotherapy drugs, including cisplatin, and has reported anxiolytic and neuroleptic properties.Pheniramine
one of the histamine h1 antagonists with little sedative action. it is used in treatment of hay fever, rhinitis, allergic dermatoses, and pruritus.Pyrilamine
a histamine h1 antagonist. it has mild hypnotic properties and some local anesthetic action and is used for allergies (including skin eruptions) both parenterally and locally. it is a common ingredient of cold remedies.Terfenadine
a selective histamine h1-receptor antagonist devoid of central nervous system depressant activity. the drug was used for allergy but withdrawn due to causing long qt syndrome.Tripelennamine
a histamine h1 antagonist with low sedative action but frequent gastrointestinal irritation. it is used to treat asthma; hay fever; urticaria; and rhinitis; and also in veterinary applications. tripelennamine is administered by various routes, including topically.Triprolidine
histamine h1 antagonist used in allergic rhinitis; asthma; and urticaria. it is a component of cough and cold medicines. it may cause drowsiness.
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.
Convert T45.0X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T45.0X5AOverview
Is T45.0X5A (Adverse effect of antiallergic and antiemetic drugs) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of antiallergic and antiemetic drugs, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T45.0X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of antiallergic and antiemetic drugs, such as an emergency visit or first evaluation.
What MS-DRG does T45.0X5A group to?
On inpatient claims, adverse effect of antiallergic and antiemetic 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 T45.0X5A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of antiallergic and antiemetic 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 T45.0X5A?
Under the General Equivalence Mappings, adverse effect of antiallergic and antiemetic drugs, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E933.0 (adv eff anallrg/antemet). 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.
