2026 ICD-10-CM Diagnosis Code T46.1X6AUnderdosing of calcium-channel blockers, initial encounter
T46.1X6A is a billable ICD-10-CM diagnosis code for underdosing of calcium-channel blockers, 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 T46.1X6A.
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 agents primarily affecting the cardiovascular system (T46). 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
Bepridil
a long-acting calcium-blocking agent with significant anti-anginal activity. the drug produces significant coronary vasodilation and modest peripheral effects. it has antihypertensive and selective anti-arrhythmia activities and acts as a calmodulin antagonist.Diltiazem
a benzothiazepine derivative with vasodilating action due to its antagonism of the actions of calcium ion on membrane functions.Felodipine
a dihydropyridine calcium antagonist with positive inotropic effects. it lowers blood pressure by reducing peripheral vascular resistance through a highly selective action on smooth muscle in arteriolar resistance vessels.Fendiline
coronary vasodilator; inhibits calcium function in muscle cells in excitation-contraction coupling; proposed as antiarrhythmic and antianginal agents.Gallopamil
coronary vasodilator that is an analog of iproveratril (verapamil) with one more methoxy group on the benzene ring.Isradipine
a potent antagonist of calcium channels that is highly selective for vascular smooth muscle. it is effective in the treatment of chronic stable angina pectoris, hypertension, and congestive cardiac failure.Lidoflazine
coronary vasodilator with some antiarrhythmic action.Nicardipine
a potent calcium channel blockader with marked vasodilator action. it has antihypertensive properties and is effective in the treatment of angina and coronary spasms without showing cardiodepressant effects. it has also been used in the treatment of asthma and enhances the action of specific antineoplastic agents.Nifedipine
a potent vasodilator agent with calcium antagonistic action. it is a useful anti-anginal agent that also lowers blood pressure.Nimodipine
a calcium channel blockader with preferential cerebrovascular activity. it has marked cerebrovascular dilating effects and lowers blood pressure.Nisoldipine
a dihydropyridine calcium channel antagonist that acts as a potent arterial vasodilator and antihypertensive agent. it is also effective in patients with cardiac failure and angina.Nitrendipine
a calcium channel blocker with marked vasodilator action. it is an effective antihypertensive agent and differs from other calcium channel blockers in that it does not reduce glomerular filtration rate and is mildly natriuretic, rather than sodium retentive.Verapamil
a calcium channel blocker that is a class iv anti-arrhythmia agent.
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 T46.1X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T46.1X6AOverview
Is T46.1X6A (Underdosing of calcium-channel blockers) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of calcium-channel blockers, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T46.1X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of calcium-channel blockers, such as an emergency visit or first evaluation.
Can T46.1X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of calcium-channel blockers, 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.
